SELECO (ZANUSSI) 20ST211 BRAVO 20" CHASSIS BS465.2 INTERNAL VIEW.

The BS465 Is the brother of the BS400 for the 90° degree CRT tubes family and was first ZANUSSI chassis with power supply developed around SIEMENS TDA4600.

It runs almost cool and is an example of absolute everlasting tv chassis pratically bugless with highly over sized components in almost all sections (see the  BU208A in Line deflection and in Power supply), further you can see the Line Deflection EHT Transformer which can serve easyly a 37 Inches without
problems !!!!!

UNITS FUNCTION DESCRIPTION CHASSIS BS465.2

- POWER SUPPLY WITH BU208A It converts the mains voltage in DC voltage available at five outputs with values of: +2OOV; +12OV; +27V (two outputs); +12.6V. These voltages are stabilized and separated from the mains.

Switched Mode Power supply Description based on TDA4601d (SIEMENS)

TDA4601 Operation. * The TDA4601 device is a single in line, 9 pin chip. Its predecessor was the TDA4600 device, the TDA4601 however has improved switching, better protection and cooler running. The (SIEMENS) TDA4601 power supply is a fairly standard parallel chopper switch mode type, which operates on the same basic principle as a line output stage. It is turned on and off by a square wave drive pulse, when switched on energy is stored in the chopper transformer primary winding in the form of a magnetic flux; when the chopper is turned off the magnetic flux collapses, causing a large back emf to be produced. At the secondary side of the chopper transformer this is rectified and smoothed for H.T. supply purposes. The advantage of this type of supply is that the high chopping frequency (20 to 70 KHz according to load) allows the use of relatively small H.T. smoothing capacitors making smoothing easier. Also should the chopper device go short circuit there is no H.T. output. In order to start up the TDA4601 I.C. an initial supply of 9v is required at pin 9, this voltage is sourced via R818 and D805 from the AC side of the bridge rectifier D801, also pin 5 requires a +Ve bias for the internal logic block. (On some sets pin 5 is used for standby switching). Once the power supply is up and running, the voltage on pin 9 is increased to 16v and maintained at this level by D807 and C820 acting as a half wave rectifier and smoothing circuit. PIN DESCRIPTIONS Pin 1 This is a 4v reference produced within the I.C. Pin 2 This pin detects the exact point at which energy stored in the chopper transformer collapses to zero via R824 and R825, and allows Q1 to deliver drive volts to the chopper transistor. It also opens the switch at pin 4 allowing the external capacitor C813 to charge from its external feed resistor R810. Pin 3 H.T. control/feedback via photo coupler D830. The voltage at this pin controls the on time of the chopper transistor and hence the output voltage. Normally it runs at Approximately 2v and regulates H.T. by sensing a proportion of the +4v reference at pin 1, offset by conduction of the photo coupler D830 which acts like a variable resistor. An increase in the conduction of transistor D830 and therefor a reduction of its resistance will cause a corresponding reduction of the positive voltage at Pin 3. A decrease in this voltage will result in a shorter on time for the chopper transistor and therefor a lowering of the output voltage and vice versa, oscillation frequency also varies according to load, the higher the load the lower the frequency etc. should the voltage at pin 3 exceed 2.3v an internal flip flop is triggered causing the chopper drive mark space ratio to extend to 244 (off time) to 1 (on time), the chip is now in over volts trip condition. Pin 4 At this pin a sawtooth waveform is generated which simulates chopper current, it is produced by a time constant network R810 and C813. C813 charges when the chopper is on and is discharged when the chopper is off, by an internal switch strapping pin 4 to the internal +2v reference, see Fig 2. The amplitude of the ramp is proportional to chopper drive. In an overload condition it reaches 4v amplitude at which point chopper drive is reduced to a mark-space ratio of 13 to 1, the chip is then in over current trip. The I.C. can easily withstand a short circuit on the H.T. rail and in such a case the power supply simply squegs quietly. Pin 4 is protected by internal protection components which limit the maximum voltage at this pin to 6.5v. Should a fault occur in either of the time constant components, then the chopper transistor will probably be destroyed. Pin 5 This pin can be used for remote control on/off switching of the power supply, it is normally held at about +7v and will cause the chip to enter standby mode if it falls below 2v. Pin 6 Ground. Pin 7 Chopper switch off pin. This pin clamps the chopper drive voltage to 1.6v in order to switch off the chopper. Pin 8 Chopper base current output drive pin. Pin 9 L.T. pin, approximately 9v under start-up conditions and 16v during normal running, Current consumption of the I.C. is typically 135mA. The voltage at this pin must reach 6.7v in order for the chip to start-up.

Semiconductor circuit for supplying power to electrical equipment, comprising a transformer having a primary winding connected, via a parallel connection of a collector-emitter path of a transistor with a first capacitor, to both outputs of a rectifier circuit supplied, in turn, by a line a-c voltage; said transistor having a base controlled via a second capacitor by an output of a control circuit acted upon, in turn by the rectified a-c line voltage as actual value and by a reference voltage; said transformer having a first secondary winding to which the electrical equipment to be supplied is connected; said transformer having a second secondary winding with one terminal thereof connected to the emitter of said transistor and the other terminal thereof connected to an anode of a first diode leading to said control circuit; said transformer having a third secondary winding with one terminal thereof connected, on the one hand, via a series connection of a third capacitor with a first resistance, to the other terminal of said third secondary winding and connected, on the other hand, to the emitter of said transistor, the collector of which is connected to said primary winding; a point between said third capacitor and said first resistance being connected to the cathode of a second diode; said control circuit having nine terminals including a first terminal delivering a reference voltage and connected, via a voltage divider formed of a third and fourth series-connected resistances, to the anode of said second diode; a second terminal of said control circuit serving for zero-crossing identification being connected via a fifth resistance to said cathode of said second diode; a third terminal of said control-circuit serving as actual value input being directly connected to a divider point of said voltage divider forming said connection of said first terminal of said control circuit to said anode of said second diode; a fourth terminal of said control circuit delivering a sawtooth voltage being connected via a sixth resistance to a terminal of said primary winding of said transformer facing away from said transistor; a fifth terminal of said control circuit serving as a protective input being connected, via a seventh resistance to the cathode of said first diode and, through the intermediary of said seventh resistance and an eighth resistance, to the cathode of a third diode having an anode connected to an input of said rectifier circuit; a sixth terminal of said control circuit carrying said reference potential and being connected via a fourth capacitor to said fourth terminal of said control circuit and via a fifth capacitor to the anode of said second diode; a seventh terminal of said control circuit establishing a potential for pulses controlling said transistor being connected directly and an eighth terminal of said control circuit effecting pulse control of the base of said transistor being connected through the intermediary of a ninth resistance to said first capacitor leading to the base of said transistor; and a ninth terminal of said control circuit serving as a power supply input of said control circuit being connected both to the cathode of said first diode as well as via the intermediary of a sixth capacitor to a terminal of said second secondary winding as well as to a terminal of said third secondary winding.

Description:

The invention relates to a blocking oscillator type switching power supply for supplying power to electrical equipment, wherein the primary winding of a transformer, in series with the emitter-collector path of a first bipolar transistor, is connected to a d-c voltage obtained by rectification of a line a-c voltage fed-in via two external supply terminals, and a secondary winding of the transformer is provided for supplying power to the electrical equipment, wherein, furthermore, the first bipolar transistor has a base controlled by the output of a control circuit which is acted upon in turn by the rectified a-c line voltage as actual value and by a set-point transmitter, and wherein a starting circuit for further control of the base of the first bipolar transistor is provided.
Such a blocking oscillator switching power supply is described in the German periodical, "Funkschau" (1975) No. 5, pages 40 to 44. It is well known that the purpose of such a circuit is to supply electronic equipment, for example, a television set, with stabilized and controlled supply voltages. Essential for such switching power supply is a power switching transistor i.e. a bipolar transistor with high switching speed and high reverse voltage. This transistor therefore constitutes an important component of the control element of the control circuit. Furthermore, a high operating frequency and a transformer intended for a high operating frequency are provided, because generally, a thorough separation of the equipment to be supplied from the supply naturally is desired. Such switching power supplies may be constructed either for synchronized or externally controlled operation or for non-synchronized or free-running operation. A blocking converter is understood to be a switching power supply in which power is delivered to the equipment to be supplied only if the switching transistor establishing the connection between the primary coil of the transformer and the rectified a-c voltage is cut off. The power delivered by the line rectifier to the primary coil of the transformer while the switching transistor is open, is interim-stored in the transformer and then delivered to the consumer on the secondary side of the transformer with the switching transistor cut off.
In the blocking converter described in the aforementioned reference in the literature, "Funkschau" (1975), No. 5, Pages 40 to 44, the power switching transistor is connected in the manner defined in the introduction to this application. In addition, a so-called starting circuit is provided. Because several diodes are generally provided in the overall circuit of a blocking oscillator according to the definition provided in the introduction hereto, it is necessary, in order not to damage these diodes, that due to the collector peak current in the case of a short circuit, no excessive stress of these diodes and possibly existing further sensitive circuit parts can occur.
Considering the operation of a blocking oscillator, this means that, in the event of a short circuit, the number of collector current pulses per unit time must be reduced. For this purpose, a control and regulating circuit is provided. Simultaneously, a starting circuit must bring the blocking converter back to normal operation when the equipment is switched on, and after disturbances, for example, in the event of a short circuit. The starting circuit shown in the literature reference "Funkschau" on Page 42 thereof, differs to some extent already from the conventional d-c starting circuits. It is commonly known for all heretofore known blocking oscillator circuits, however, that a thyristor or an equivalent circuit replacing the thyristor is essential for the operation of the control circuit.
It is accordingly an object of the invention to provide another starting circuit. It is a further object of the invention to provide a possible circuit for the control circuit which is particularly well suited for this purpose. It is yet another object of the invention to provide such a power supply which is assured of operation over the entire range of line voltages from 90 to 270 V a-c, while the secondary voltages and secondary load variations between no-load and short circuit are largely constant.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a blocking oscillator-type switching power supply for supplying power to electrical equipment wherein a primary winding of a transformer, in series with an emitter-collector path of a first bipolar transistor, is connected to a d-c voltage obtained by rectification of a line a-c voltage fed-in via two external supply terminals, a secondary winding of the transformer being connectible to the electrical equipment for supplying power thereto, the first bipolar transistor having a base controlled by the output of a control circuit acted upon, in turn, by the rectified a-c line voltage as actual value and by a set-point transmitter, and including a starting circuit for further control of the base of the first bipolar transistor, including a first diode in the starting circuit having an anode directly connected to one of the supply terminals supplied by the a-c line voltage and a cathode connected via a resistor to an input serving to supply power to the control circuit, the input being directly connected to a cathode of a second diode, the second diode having an anode connected to one terminal of another secondary winding of the transformer, the other secondary winding having another terminal connected to the emitter of the first bipolar transmitter.
In accordance with another feature of the invention, there is provided a second bipolar transistor having the same conduction type as that of the first bipolar transistor and connected in the starting circuit with the base thereof connected to a cathode of a semiconductor diode, the semiconductor diode having an anode connected to the emitter of the first bipolar transistor, the second bipolar transistor having a collector connected via a resistor to a cathode of the first diode in the starting circuit, and having an emitter connected to the input serving to supply power to the control circuit and also connected to the cathode of the second diode which is connected to the other secondary winding of the transformer.
In accordance with a further feature of the invention, the base of the second bipolar transistor is connected to a resistor and via the latter to one pole of a first capacitor, the anode of the first diode being connected to the other pole of the first capacitor.
In accordance with an added feature of the invention, the input serving to supply power to the control circuit is connected via a second capacitor to an output of a line rectifier, the output of the line rectifier being directly connected to the emitter of the first bipolar transistor.
In accordance with an additional feature of the invention, the other secondary winding is connected at one end to the emitter of the first bipolar transistor and to a pole of a third capacitor, the third capacitor having another pole connected, on the one hand, via a resistor, to the other end of the other secondary winding and, on the other hand, to a cathode of a third diode, the third diode having an anode connected via a potentiometer to an actual value input of the control circuit and, via a fourth capacitor, to the emitter of the first bipolar transistor.
In accordance with yet another feature of the invention, the control circuit has a control output connected via a fifth capacitor to the base of the first bipolar transistor for conducting to the latter control pulses generated in the control circuit.
In accordance with a concomitant feature of the invention, there is provided a sixth capacitor shunting the emitter-collector path of the first transistor.
Other features which are considered as characteristic for the invention are set forth in the appended claim.
Although the invention is illustrated and described herein as embodied in a blocking oscillator type switching power supply, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIGS. 1 and 2 are circuit diagrams of the blocking oscillator type switching power supply according to the invention; and

FIG. 3 is a circuit diagram of the control unit RS of FIGS. 1 and 2.

Referring now to the drawing and, first, particularly to FIG. 1 thereof, there is shown a rectifier circuit G in the form of a bridge current, which is acted upon by a line input represented by two supply terminals 1' and 2'. Rectifier outputs 3' and 4' are shunted by an emitter-collector path of an NPN power transistor T1 i.e. the series connection of the so-called first bipolar transistor referred to hereinbefore with a primary winding I of a transformer Tr. Together with the inductance of the transformer Tr, the capacitance C1 determines the frequency and limits the opening voltages of the switch embodied by the first transistor T1. A capacitance C2, provided between the base of the first transistor T1 and the control output 7,8 of a control circuit RS, separates the d-c potentials of the control or regulating circuit RS and the switching transistor T1 and serves for addressing this switching transistor T1 with pulses. A resistor R1 provided at the control output 7,8 of the control circuit RS is the negative-feedback resistor of both output stages of the control circuit RS. It determines the maximally possible output pulse current of the control circuit RS. A secondary winding II of the transformer Tr takes over the power supply of the control circuit, in steady state operation, via the diode D1. To this end, the cathode of this diode D1 is directly connected to a power supply input 9 of the control circuit RS, while the anode thereof is connected to one terminal of the secondary winding II. The other terminal of the secondary winding II is connected to the emitter of the power switching transistor T1.

The cathode of the diode D1 and, therewith, the power supply terminal 9 of the control circuits RS are furthermore connected to one pole of a capacitor C3, the other pole of which is connected to the output 3' of the rectifier G. The capacitance of this capacitor C3 thereby smoothes the positive half-wave pulses and serves simultaneously as an energy storage device during the starting period. Another secondary winding III of the transformer Tr is connected by one of the leads thereof likewise to the emitter of the first transistor T1, and by the other lead thereof via a resistor R2, to one of the poles of a further capacitor C4, the other pole of which is connected to the first-mentioned lead of the other secondary winding III. This second pole of the capacitor C4 is simultaneously connected to the output 3' of the rectifier circuit G and, thereby, via the capacitor C3, to the cathode of the diode D1 driven by the secondary winding II of the transformer Tr as well as to the power supply input 9 of the control circuit RS and, via a resistor R9, to the cathode of a second diode D4. The second pole of the capacitor C4 is simultaneously connected directly to the terminal 6 of the control circuit RS and, via a further capacitor C 6, to the terminal 4 of the control circuit RS as well as, additionally, via the resistor R6, to the other output 4' of the rectifier circuit G. The other of the poles of the capacitor C4 acted upon by the secondary winding II is connected via a further capacitor C5 to a node, which is connected on one side thereof, via a variable resistor R4, to the terminals 1 and 3 of the control circuit RS, with the intermediary of a fixed resistor R5 in the case of the terminal 1. On the other side of the node, the latter and, therefore, the capacitor C5 are connected to the anode of a third diode D2, the cathode of which is connected on the one hand, to the resistor R2 mentioned hereinbefore and leads to the secondary winding III of the transformer Tr and, on the other hand, via a resistor R3 to the terminal 2 of the control circuit RS.

The nine terminals of the control circuit RS have the following purposes or functions:

Terminal 1 supplies the internally generated reference voltage to ground i.e. the nominal or reference value required for the control or regulating process;

Terminal 2 serves as input for the oscillations provided by the secondary winding III, at the zero point of which, the pulse start of the driving pulse takes place;

Terminal 3 is the control input, at which the existing actual value is communicated to the control circuit RS, that actual value being generated by the rectified oscillations at the secondary winding III;

Terminal 4 is responsive to the occurrence of a maximum excursion i.e. when the largest current flows through the first transistor T1 ;

Terminal 5 is a protective input which responds if the rectified line voltage drops too sharply; Terminal 6 serves for the power supply of the control process and, indeed, as ground terminal;

Terminal 7 supplies the d-c component required for charging the coupling capacitor C2 leading to the base of the first transistor T1 ;

Terminal 8 supplies the control pulse required for the base of the first transistor T1 ; and

Terminal 9 serves as the first terminal of the power supply of the control circuit RS.

Further details of the control circuit RS are described hereinbelow.

The capacity C3 smoothes the positive half-wave pulses which are provided by the secondary winding II, and simultaneously serves as an energy storage device during the starting time. The secondary winding III generates the control voltage and is simultaneously used as feedback. The time delay stage R2 /C4 keeps harmonics and fast interference spikes away from the control circuit RS. The resistor R3 is provided as a voltage divider for the second terminal of the control circuit RS. The diode D2 rectifies the control pulses delivered by the secondary winding III. The capacity C5 smoothes the control voltage. A reference voltage Uref, which is referred to ground i.e. the potential of terminal 6 is present at the terminal 1 of the control circuit RS. The resistors R4 and R5 form a voltage divider of the input-difference control amplifier at the terminal 3. The desired secondary voltage can be set manually via the variable resistor R4. A time-delay stage R6 /C6 forms a sawtooth rise which corresponds to the collector current rise of the first bipolar transistor T1 via the primary winding I of the transformer Tr. The sawtooth present at the terminal 4 of the control circuit RS is limited there between the reference voltage 2 V and 4 V. The voltage divider R7 /R8 (FIG. 2), brings to the terminal 5 of the control circuit RS the enabling voltage for the drive pulse at the output 8 of the control circuit RS.

The diode D4, together with the resistor R9 in cooperation with the diode D1 and the secondary winding II, forms the starting circuit provided, in accordance with the invention. The operation thereof is as follows:

After the switching power supply is switched on, d-c voltages build up at the collector of the switching transistor T1 and at the input 4 of the control circuit RS, as a function in time of the predetermined time constants. The positive sinusoidal half-waves charge the capacitor C3 via the starting diode D4 and the starting resistor R9 in dependence upon the time constant R9.C3. Via the protective input terminal 5 and the resistor R11 not previously mentioned and forming the connection between the resistor R9 and the diode D1, on the one hand, and the terminal 5 of the control circuit RS, on the other hand, the control circuit RS is biased ready for switching-on, and the capacitor C2 is charged via the output 7. When a predetermined voltage value at the capacitor C3 or the power supply input 9 of the control circuit RS, respectively, is reached, the reference voltage i.e. the nominal value for the operation of the control voltage RS, is abruptly formed, which supplies all stages of the control circuit and appears at the output 1 thereof. Simultaneously, the switching transistor T1 is switched into conduction via the output 8. The switching of the transistor T1 at the primary winding T of the transformer Tr is transformed to the second secondary winding II, the capacity C3 being thereby charged up again via the diode D1. If sufficient energy is stored in the capacitor C3 and if the re-charge via the diode D1 is sufficient so that the voltage at a supply input 9 does not fall below the given minimum operating voltage, the switching power supply then remains connected, so that the starting process is completed. Otherwise, the starting process described is repeated several times.

In FIG. 2, there is shown a further embodiment of the circuit for a blocking oscillator type switching power supply, according to the invention, as shown in FIG. 1. Essential for this circuit of FIG. 2 is the presence of a second bipolar transistor T2 of the type of the first bipolar transistor T1 (i.e. in the embodiments of the invention, an npn-transistor), which forms a further component of the starting circuit and is connected with the collector-emitter path thereof between the resistor R9 of the starting circuit and the current supply input 9 of the control circuit RS. The base of this second transistor T2 is connected to a node which leads, on the one hand, via a resistor R10 to one electrode of a capacitor C7, the other electrode of which is connected to the anode of the diode D4 of the starting circuit and, accordingly, to the terminal 1' of the supply input of the switching power supply G. On the other hand, the last-mentioned node and, therefore, the base of the second transistor T2 are connected to the cathode of a Zener diode D3, the anode of which is connected to the output 3' of the rectifier G and, whereby, to one pole of the capacitor C3, the second pole of which is connected to the power supply input 9 of the control circuit RS as well as to the cathode of the diode D1 and to the emitter of the second transistor T2. In other respects, the circuit according to FIG. 2 corresponds to the circuit according to FIG. 1 except for the resistor R11 which is not necessary in the embodiment of FIG. 2, and the missing connection between the resistor R9 and the cathode of the diode D1, respectively, and the protective input 5 of the control circuit RS.

Regarding the operation of the starting circuit according to FIG. 2, it can be stated that the positive sinusoidal half-wave of the line voltage, delayed by the time delay stage C7, R10 drives the base of the transistor T2 in the starting circuit. The amplitude is limited by the diode D3 which is provided for overvoltage protection of the control circuit RS and which is preferably incorporated as a Zener diode. The second transistor T2 is switched into conduction. The capacity C3 is charged, via the serially connected diode D4 and the resistor R9 and the collector-emitter path of the transistor T2, as soon as the voltage between the terminal 9 and the terminal 6 of the control circuit RS i.e. the voltage U9, meets the condition U9 <[UDs -UBE (T2)].

Because of the time constant R9.C3, several positive half-waves are necessary in order to increase the voltage U9 at the supply terminal 9 of the control circuit RS to such an extent that the control circuit RS is energized. During the negative sine half-wave, a partial energy chargeback takes place from the capacitor C3 via the emitter-base path of the transistor T2 of the starting circuit and via the resistor R10 and the capacitor C7, respectively, into the supply network. At approximately 2/3 of the voltage U9, which is limited by the diode D3, the control circuit RS is switched on. At the terminal 1 thereof, the reference voltage Uref then appears. In addition, the voltage divider R5 /R4 becomes effective. At the terminal 3, the control amplifier receives the voltage forming the actual value, while the first bipolar transistor T1 of the blocking-oscillator type switching power supply is addressed pulsewise via the terminal 8.

Because the capacitor C6 is charged via the resistor R6, a higher voltage than Uref is present at the terminal 4 if the control circuit RS is activated. The control voltage then discharges the capacitor C6 via the terminal 4 to half the value of the reference voltage Uref, and immediately cuts off the addressing input 8 of the control circuit RS. The first driving pulse of the switching transistor T1 is thereby limited to a minimum of time. The power for switching-on the control circuit RS and for driving the transistor T1 is supplied by the capacitor C3. The voltage U9 at the capacitor C3 then drops. If the voltage U9 drops below the switching-off voltage value of the control circuit RS, the latter is then inactivated. The next positive sine half-wave would initiate the starting process again.

By switching the transistor T1, a voltage is transformed in the secondary winding II of the transformer Tr. The positive component is rectified by the diode D1, recharing of the capacitor C3 being thereby provided. The voltage U9 at the output 9 does not, therefore, drop below the minimum value required for the operation of the control circuit RS, so that the control circuit RS remains activated. The power supply continues to operate in the rhythm of the existing conditions. In operation, the voltage U9 at the supply terminal 9 of the control circuit RS has a value which meets the condition U9 >[UDs -UBE (T2)], so that the transistor T2 of the starting circuit remains cut off.

For the internal layout of the control circuit RS, the construction shown, in particular, from FIG. 3 is advisable. This construction is realized, for example, in the commercially available type TDA 4600 (Siemens AG).

The block diagram of the control circuit according to FIG. 3 shows the power supply thereof via the terminal 9, the output stage being supplied directly whereas all other stages are supplied via Uref. In the starting circuit, the individual subassemblies are supplied with power sequentially. The d-c output voltage potential of the base current gain i.e. the voltage for the terminal 8 of the control circuit RS, and the charging of the capacitor C2 via the terminal 7 are formed even before the reference voltage Uref appears. Variations of the supply voltage U9 at terminal 9 and the power fluctuations at the terminal 8/terminal 7 and at the terminal 1 of the control circuit RS are leveled or smoothed out by the voltage control. The temperature sensitivity of the control circuit RS and, in particular, the uneven heating of the output and input stages and input stages on the semiconductor chip containing the control circuit in monolithically integrated form are intercepted by the temperature compensation provided. The output values are constant in a specific temperature range. The message for blocking the output stage, if the supply voltage at the terminal 9 is too low, is given also by this subassembly to a provided control logic.

The outer voltage divider of the terminal 1 via the resistors R5 and R4 to the control tap U forms, via terminal 3, the variable side of the bridge for the control amplifier formed as a differential amplifier. The fixed bridge side is formed by the reference voltage Uref via an internal voltage divider. Similarly formed are circuit portions serving for the detection of an overload short circuit and circuit portions serving for the "standby" no-load detection, which can be operated likewise via terminal 3.

Within a provided trigger circuit, the driving pulse length is determined as a function of the sawtooth rise at the terminal 4, and is transmitted to the control logic. In the control logic, the commands of the trigger circuit are processed. Through the zero-crossing identification at input 2 in the control circuit RS, the control logic is enabled to start the control input only at the zero point of the frequency oscillation. If the voltages at the terminal 5 and at the terminal 9 are too low, the control logic blocks the output amplifier at the terminal 8. The output amplifier at the terminal 7 which is responsible for the base charge in the capacitor C2, is not touched thereby.

The base current gain for the transistor T1 i.e. for the first transistor in accordance with the definition of the invention, is formed by two amplifiers which mutually operate on the capacitor C2. The roof inclination of the base driving current for the transistor T1 is impressed by the collector current simulation at the terminal 4 to the amplifier at the terminal 8. The control pulse for the transistor T1 at the terminal 8 is always built up to the potential present at the terminal 7. The amplifier working into the terminal 7 ensures that each new switching pulse at the terminal 8 finds the required base level at terminal 7.

Supplementing the comments regarding FIG. 1, it should also be mentioned that the cathode of the diode D1 connected by the anode thereof to the one end of the secondary winding II of the transformer Tr is connected via a resistor R11 to the protective input 5 of the control circuit RS whereas, in the circuit according to FIG. 2, the protective input 5 of the control circuit RS is supplied via a voltage divider R8, R7 directly from the output 3', 4' of the rectifier G delivering the rectified line a-c voltage, and which obtains the voltage required for executing its function. It is evident that the first possible manner of driving the protective input 5 can be used also in the circuit according to FIG. 2, and the second possibility also in a circuit in accordance with FIG. 1.

The control circuit RS which is shown in FIG. 3 and is realized in detail by the building block TDA 4600 and which is particularly well suited in conjunction with the blocking oscillator type switching power supply according to the invention has 9 terminals 1-9, which have the following characteristics, as has been explained in essence hereinabove:

Terminal 1 delivers a reference voltage Uref which serves as the constant-current source of a voltage divider R5.R4 which supplies the required d-c voltages for the differential amplifiers provided for the functions control, overload detection, short-circuit detection and "standby"-no load detection. The dividing point of the voltage divider R5 -R4 is connected to the terminal 3 of the control circuit RS. The terminal 3 provided as the control input of RS is controlled in the manner described hereinabove as input for the actual value of the voltage to be controlled or regulated by the secondary winding III of the transformer Tr. With this input, the lengths of the control pulses for the switching transistor T1 are determined.

Via the input provided by the terminal 2 of the control circuit RS, the zero-point identification in the control circuit is addressed for detecting the zero-point of the oscillations respectively applied to the terminal 2. If this oscillation changes over to the positive part, then the addressing pulse controlling the switching transistor T1 via the terminal 8 is released in the control logic provided in the control circuit.

A sawtooth-shaped voltage, the rise of which corresponds to the collector current of the switching transistor T1, is present at the terminal 4 and is minimally and maximally limited by two reference voltages. The sawtooth voltage serves, on the one hand as a comparator for the pulse length while, on the other hand, the slope or rise thereof is used to obtain in the base current amplification for the switching transistor T1, via the terminal 8, a base drive of this switching transistor T1 which is proportional to the collector current.

The terminal 7 of the control circuit RS as explained hereinbefore, determines the voltage potential for the addressing pulses of the transistor T2. The base of the switching transistor T1 is pulse-controlled via the terminal 8, as described hereinbefore. Terminal 9 is connected as the power supply input of the control circuit RS. If a voltage level falls below a given value, the terminal 8 is blocked. If a given positive value of the voltage level is exceeded, the control circuit is activated. The terminal 5 releases the terminal 8 only if a given voltage potential is present.

Foreign References:
DE2417628A1 1975-10-23 363/37
DE2638225A1 1978-03-02 363/49
Other References:
Grundig Tech. Info. (Germany), vol. 28, No. 4, (1981).
IBM Technical Disclosure Bulletin, vol. 19, No. 3, pp. 978, 979, Aug. 1976.
German Periodical, "Funkschau", (1975), No. 5, pp. 40 to 44.

Inventors:

Peruth, Gunther (Munich, DE) Siemens Aktiengesellschaft (Berlin and Munich, DE)




- FRAME DEFLECTION WITH TDA1170 This p.c.b. generates a sawtooth
voltage at frame frequency which is used for driving the vertical deflection yoke. It supplies a
similar voltage to the "pincushion" section of the synchro. separator p.c.b. to obtain the E/W pincushion correction. It supplies a frame frequency pulse which is used for the luminance, chrominance and video amplifier p.c.b. blankings. It receives the vertical synchro.
from the synchro. separator p.c.b. and receives from the chassis a voltage proportional to the beam current.

- BS399.0 LUMINANCE AND CHROMINANCE + RGB AMPLIFIER This p.c.b. processes the
complete composite video signal coming from the IF p.c.b. andsupplies the R-G-B signals to
the picture tube.











- BS398 TUNER + AFC + IF Conversion of the RF signal into an IF signal
(video carrier:39.5 M z; audio carrier:33.5 MHZ).
Detection of the IF signal into low frequency video and audio signals.











TDA2541 IF AMPLIFIER WITH DEMODULATOR AND AFC
DESCRIPTION
The TDA2540 and 2541 are IF amplifier and A.M.
demodulator circuits for colour and black and white
television receivers using PNP or NPN tuners. They
are intended for reception of negative or positive
modulation CCIR standard.
They incorporate the following functions : .Gain controlled amplifier .Synchronous demodulator .White spot inverter .Video preamplifier with noise protection .Switchable AFC .AGC with noise gating .Tuner AGC output (NPN tuner for 2540)-(PNP
tuner for 2541) .VCR switch for video output inhibition (VCR
play back).









- BS389 REMOTE CONTROL DECODER WITH ITT SAA1251 This p.c.b. enables remote
control of the following functions: selection of 16 programmes; "+" or "-" adjustment; brightness
saturation adjustment; silencing; TV receiver switching.











- BS388.2 TUNING MEMORY AND SEARCH Remote control p.c.b. The display indicates the programme selected. Furthermore,this p.c.b. includes all pushbuttons for clock
adjustment.No adjustments needed. Automatic searching of a TV station through a start command. Manual searching of a TV station through two commands (increment and decrement).
Inclusion-exclusion of the AFC circuit with LED display. Band indication displayed on
three LEDs. Tuning level indication with five LEDs. Memorization of 16 selected
programmes manually or remote control.
 Features The MOTOROLA Memotronic with MC14429P-A,   MC14426P,   UAA1008A-DP, 


- BS392.2 ST-BY SUPPLY AND OPTOCOUPLER START STOP FEATURE. The p.c.b. includes circuits relevant to: mains filter, degaussing, remote control supply, start remote control.
No adjustments needed. It includes circuits for clock supply and for switch-ON programming. It has the  phototransistor + infrared emitter joined in a plastic tube to obtain power on off separate from mains



- BS401 This p.c.b. receives the audio signal (not adjusted in volume) coming from p.c.b. BS 398, it adjusts it in amplitude and tone, it amplifies it and sends it to drive the two receiver’s loudspeakers (tweeter and woofer).

TDA1170 vertical deflection FRAME DEFLECTION INTEGRATED CIRCUITGENERAL DESCRIPTION f The TDA1170 and TDA1270 are monolithic integrated
circuits designed for use in TV vertical deflection systems. They are manufactured using
the Fairchild Planar* process.
Both devices are supplied in the 12-pin plastic power package with the heat sink fins bent
for insertion into the printed circuit board.
The TDA1170 is designed primarily for large and small screen black and white TV
receivers and industrial TV monitors. The TDA1270 is designed primarily for driving
complementary vertical deflection output stages in color TV receivers and industrial
monitors.
APPLICATION INFORMATION (TDA1170)
The vertical oscillator is directly synchronized by the sync pulses (positive or negative); therefore its free
running frequency must be lower than the sync frequency. The use of current feedback causes the yoke
current to be independent of yoke resistance variations due to thermal effects, Therefore no thermistor is
required in series with the yoke. The flyback generator applies a voltage, about twice the supply voltage, to
the yoke. This produces a short flyback time together with a high useful power to dissipated power
ratio.

BU208(A)

Silicon NPN
npn transistors,pnp transistors,transistors
Category: NPN Transistor, Transistor
MHz: <1 MHz
Amps: 5A
Volts: 1500V
HIGH VOLTAGE CAPABILITY
JEDEC TO-3 METAL CASE.

DESCRIPTION
The BU208A, BU508A and BU508AFI are
manufactured using Multiepitaxial Mesa
technology for cost-effective high performance
and use a Hollow Emitter structure to enhance
switching speeds.

APPLICATIONS:
* HORIZONTAL DEFLECTION FOR COLOUR TV With 110° or even 90° degree of deflection angle.

ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
VCES Collector-Emit ter Voltage (VBE = 0) 1500 V
VCEO Collector-Emit ter Voltage (IB = 0) 700 V
VEBO Emitter-Base Voltage (IC = 0) 10 V
IC Collector Current 8 A
ICM Collector Peak Current (tp < 5 ms) 15 A
TO - 3 TO - 218 ISOWATT218
Ptot Total Dissipation at Tc = 25 oC 150 125 50 W
Tstg Storage Temperature -65 to 175 -65 to 150 -65 to 150 oC
Tj Max. Operating Junction Temperature 175 150 150 °C



SELECO (ZANUSSI) 20ST211 BRAVO 20" CHASSIS BS465.2 Television receiver with an automatic station finding arrangement:

The present invention relates to a television tuning device, comprising a circuit for continuously scanning at least one band of receivable frequencies, and having control means for starting and stopping the said scanning procedure and a terminal for applying a switch signal for switching from a first band-scanning speed to a second band-scanning speed slower than the first.
The name usually applied to a unit consisting of circuits of this type for selecting and memorising a given number of preferred channels is "station memory".
Many types of station memories are already being sold on the market which can be divided into two main groups: those with automatic and those with manual television channel searching.
The automatic types are fitted with electronic searching circuits which locate television channels automatically when started by the user. This is done by scanning a given band (VHF or UHF, for example) and stopping on the located channel. Data relative to the located channel can then be memorised by the user in a memory circuit and the same channel recalled whenever required by simply pressing a button which recalls the said data from the memory and supplies it to the channel selection circuit.
This type of circuit is also fitted with components which sense, during search, if a television channel has been tuned into and disable automatic searching to prevent television band scanning from continuing. Most of these circuits are fitted with a phase detector which senses the coincidence between the sync signals received and those regenerated in the receiver (in particular, the flyback signal).
Manual station memories, on the other hand, are fitted with controls which, when activated by the user, start a device for scanning a given television band. These controls also stop the said device when required by the user. When the user sees the required channel appear on the screen, the device is stopped to disable search and enable the channel to be memorised in the appropriate circuit.
In these cases, the simplest way of starting and stopping the search is to fit the circuits with a button which, when pressed, supplies a search-start signal and, when released, stops the searching operation. For best tuning, two buttons are usually provided for band scanning in both directions.
Both the types discussed up to now present drawbacks. In the case of automatic station memories, for example, tuning quality depends on correct operation of all the search-stop circuits and the automatic tuning circuit (AFC=automatic frequency control). Even in cases where these circuits are operating correctly, tuning could still be impaired by noise or amplitude distortion on the received signal.
Tuning quality on manual station memories, on the other hand, depends on the tuning ability of the user. Television receivers can be manipulated by anybody not all of whom are gifted with this ability. A further drawback of manual station memories is that the user has very little time in which to decide whether the received channel is the right one and to estimate tuning quality. If the whole television band is to be scanned in a reasonable length of time (let us say, the UHF band in one minute) band-scanning speed needs to be fairly high. Consequently, if the user is not quick enough in sending out the search-stop control signal, it is more than likely that the control will be sent when the required television channel has been overshot. If, by chance, there are two channels close to one another, the searching device may even stop on the second of the two, thus confusing the user who will not know which of the two channels he has tuned into.
The aim of the present invention is to provide a tuning device to overcome these problems.
With this aim in view, the present invention provides a television tuning device comprising a circuit for continuously scanning at least one band of receivable frequencies, manual control means for starting and stopping the said scanning procedure, a terminal for applying a switch signal for switching from a first band-scanning speed to a second band-scanning speed lower than the first, and detection means for detecting the presence of a television channel by comparing the received sync signals with local signals generated in the television receiver, and applying a switch signal to the said terminal for switching from the said first scanning speed to the said second scanning speed in the presence of the said switch signal, so that the band scanning continues at said lower speed until the manual control means produce the stopping scanning procedure.

MOTOROLA TUNING MEMORY / MEMOTRONIC SYSTEM TECHNOLOGY.In a radio or television receiver containing an automatic station finder with a digital counter, a clock generator, and a digital-to-analog converter forming the tuning voltage for the varactors, a recall memory consisting of two series-connected parallel memories is connected in parallel with the digital counter. At a stop signal from the

automatic station finder the first parallel memory records the instantaneous count of the digital counter; at an automatic-station-finding start signal the second parallel memory, to which the parallel input of the digital counter is connected, records the contents of the first parallel memory.


1. A receiver having automatic station finding capability, comprising:
means for tuning said receiver in response to an applied voltage;
a controllable pulse generator;
means for starting said pulse generator;
circulating counter means having parallel inputs and outputs, a stepping input and a set input, said stepping input connected to and responsive to pulses from said pulse generator for providing a variable digital output;
digital-to-analog convert

ing means for converting the variable digital output from said counter means to a variable analog voltage, said voltage being applied to said tuning means, so that the receiver is tuned to a frequency corresponding to the analog voltage;
means for sensing a received signal and for providing a stop signal to the pulse generator in response thereto, whereby said generator stops providing pulses and the analog voltage remains constant keeping the receiver tuned to the received signal;
memory means having parallel inputs connected to the parallel outputs of said counter means and parallel outputs connected to the parallel inputs of said counter means;
means associated with said memory means for causing the memory means to store a particular digital output from said counter means; and
means associated with the set input of said counter means for selectively causing the digital signal at the counter input to be transferred to the counter output.


2. A receiver as described in claim 1, wherein the memory means comprises: two series connected parallel memories each having a transfer input, a first of said parallel memories having parallel inputs connected to the parallel outputs of the counter means and having the transfer input connected to the stop signal means, a second of said parallel memories having parallel outputs connected to the parallel inputs of the counter means and having the transfer input connected to the means for starting said pulse generator.

3. A receiver as described in claim 2, wherein each of said parallel memories comprises a plurality of semiconductor voltage flip-flops.

4. A receiver as described in claim 2, wherein the two series connected parallel memories are incorporated in an integrated circuit module with the counter means.

5. A receiver as described in claim 2, wherein the transfer input of the first parallel memory is also connected to the means associated with the set input of the counter means.

6. A receiver as described in claim 1, additionally comprising:
an additional memory means having parallel inputs and outputs;
means for connecting the inputs of said additional memory means to the counter means output and the outputs of said additional memory means to the counter inputs;
means for causing said additional memory means to store a digital output; and
means for transferring the stored digital output to the counter means input through the connecting means.


7. A receiver as described in claim 6, additionally comprising gate means disposed at the outputs of the memory means and the additional memory means for selectively connecting either the additional memory means or the memory means to the input of the counter.

8. A receiver as described in claim 6, wherein the additional memory means comprises a plurality of memories and the connecting means comprises a plurality of station switches corresponding in number to the number of additional memories.

9. A receiver as described in claim 1, wherein each memory means comprises a number of flip-flops corresponding to the number of digits to be stored.

Description:

The p

resent invention relates to a radio or television receiver with an automatic station finding arrangement which contains a pulse generator, a circulating counter formed from semiconductor counting flip-flops and having parallel inputs, a digital-to-analog converter converting the count of the counter to a tuning voltage, and a start-stop circuit acting on the flow of counting pulses and controlled over a start and at least one stop line, and with a parallel memory connected between the parallel outputs and parallel inputs of the counter.
Such a radio receiver is known from, e.g., the journal "Funkschau 1971", pp. 535 to 538 and 587 to 589. With the aid of the free-running pulse generator, the up-counter, and the digital-to-analog converter, the automatic station finding arrangement generates a sawtoothlike tuning voltage for the varactors contained as frequency-setting tuning elements in the resonant circuits of the receiver's radio-frequency portion. If a transmitter is received which meets the receiving criteria set in the receiver, the pulse generator is stopped so that the tuning voltage now remains constant until the operator continues the automatic station finding operation by actuating a start switch.
It is frequently desirable to tune in once again the station at which the start switch for automatic station finding was actuated last - either for comparison or because of the more interesting program. To do this in the case of a receiver with provision for unidirectional automatic station search, the entire search range must be scanned once or several times by repeatedly actuating the start switch, depending on whether the desired station is detected immediately or not.
It is the object of the invention to provide measures for a receiver of the kind referred to by way of introduction which permit the transmitter received before the actuation of the start switch to be found again with a high degree of safety by simple manipulation.
The invention is characterized in that the parallel memory consists of two series-connected parallel memories having one transfer input each, that the transfer input of the (first) parallel memory, whose parallel inputs are connected to the parallel outputs of the counter, are connected directly or indirectly to the stop line, that the transfer input of the (second) parallel memory, whose parallel outputs are connected to the parallel inputs of the counter, is connected directly or indirectly to the start line, that the counter has a set input for through-connecting the parallel inputs of the counter to the flip-flops of the counter, and that a recall switch is connected to the set input of the counter.
Particularly advantageously, the memory locations of the two series-connected parallel memories are storage flip-flops using semiconductor technology. In that case it is possible to arrange the counter and the parallel memories on a common chip of an integrated-circuit module. Such a module has only two terminals more than a module formed by the counter only.
The measures characterized by the invention thus require, aside from an additional recall switch, no additional space and involve nearly no additional expense. To recall the station previously tuned in it is only necessary to depress a button, for example, whereby the receiver is safely tuned to the station's carrier wave even if at the instant of the depression the local received field strength is temporarily too low for sufficient reception.
The invention will now be described in more detail with reference to the accompanying drawing, showing, by way of example, two embodiments of the invention, and wherein:
FIG. 1 is a block diagram showing the radio- and intermediate-frequency portions of a receiver with an automatic station finding arrangement and a recall arrangement;
FIG. 2 shows diagrams a to g explaining the operation of the recall storage, and
FIG. 3 shows a receiver similar to the one of FIG. 1 in which the automatic station finding counter and the recall memories are arranged together on the chip of an integrated-circuit module.
The receivers shown in the block diagrams of FIGS. 1 and 3 have a radio-frequency-receiving section 1, an intermediate-frequency amplifier 2, and a demodulator section 3, to whose output 4 are connected the arrangements processing the modulation frequency. The tunable resonant circuits of the radio-frequency section contain varactors as tuning elements. Connected to the radio-frequency section is an automatic station finding arrangement in which a digital-to-analog converter 5 generates from the count of a digital counter 7, which receives signals at a stepping input T and advances at the rate of a pulse generator 6, a nearly sawtooth-shaped tuning voltage for the varactors. With a sufficient received field strength at the antenna 8 of the receiver a signal is formed in the demodulator section 3 which signal can be used as stop signal 9 to change the state of a start-stop circuit 10 which may be a flip flop. In the "stop" state the start-stop circuit interrupts the pulse generation or the pulse flow in the pulse generator so that the receiver remains tuned to the station being received. By operating a start-button switch 11 a start signal 12 is generated in the receiver which signal places the start-stop circuit in the "automatic station finding" state and thus continues the automatic station finding operation until next station meeting the receiver's receiving requirements is received.
In the embodiment of FIG. 1, two series-connected parallel memories 15 and 16 are connected, respectively, over two groups of lines 13 and 14 consisting of n lines each, between the n outputs Q ₁₁ to Q _n1 and the parallel inputs A ₁₁ to A _n1 of the digital counter 7 containing n counting flip-flops. Each parallel memory contains n storage flip-flops and, besides the parallel bit inputs and outputs B and X, a transfer input S. If a transfer signal appears at the transfer input, the parallel memory records the bit word applied its parallel inputs B ₁ to B _n , which erases the previously entered bit word and now, in turn, appears at the memory outputs X ₁ to X _n .
The transfer input S of the parallel memory 15, whose parallel inputs are connected over the group of lines 13 to the outputs of the counter 7, is connected to the stop line 17, while the transfer input S of the parallel memory 16, whose parallel outputs are connected over the group of lines 14 to the parallel inputs of the counter 7, is connected to the start line 18.
Connected to a set input P of the digital counters 7 is a switch 19 whose operation generates a set signal. The set signal sets the counter to a count which is equal to the bit word at the parallel inputs A ₁ to A _n of the counter. At the same time, the set signal acts over the line 20 and via an OR circuit provided for isolation on the transfer input S of the first parallel memory 15.
The diagrams a to g of FIG. 2 explain the operation of the automatic station finding arrangement in conjunction with the recall memories. In diagram a each of the blocks II, III, etc. represents the bit word for a count of the digital counter 7. The blocks in the diagrams b and c are the bit words which are stored in the parallel memories 15 and 16 and can be taken off the latter's parallel outputs, the blocks with equal Roman numerals (e.g. V) representing equal bit words. The diagram d shows the counting pulses 22 for the digital counter 7, the diagram e the stop pulses 9, the diagram f the start pulses 12, and the diagram g the set pulse 23 triggered by the recall switch 19.
The respective count from which the digital-to-analog converter 5 forms the tuning voltage for the varactors is applied simultaneously to the input of the digital-to-analog converter and, as a bit word (e.g. II, III, IV . . . , diagram a), to the input of the first parallel memory 15. At the occurence of a stop signal 9 during the automatic station finding operation, the stop signal 9 acts as a transfer signal on the first par

allel memory 15, and the count (e.g. V, diagram a) at which the stop pulse (e.g. 9a) was generated is entered into the first parallel memory 15 (V in diagram b). At the next start pulse 12a triggered via the start-button switch 11 the automatic station finding operation begins anew, starting from the instantaneous count (e.g. V, diagram a) of the counter. The start signal (12a in diagram f) acts as a transfer signal on the transfer input S of the second parallel memory 16, whereby the second parallel memory takes over the bit word (e.g. V) of the first. The next stop signal (e.g. 9b, diagram e) at a new count (e.g. VIII, diagram a) stops the automatic station search and enters the new count as a bit word (e.g. VIII, diagram b) into the first parallel memory 15.
If the operator operates the recall switch 19 so as to recall the setting to the previously received station, the set pulse 23 triggered by the recall switch sets the counter 7 to the count (e.g. V, diagram a) of the bit word (e.g. V, diagram c) stored in the second parallel memory 16, and the newly set count is entered into the first parallel memory 15 (e.g. V, diagram b). The next start signal (e.g. 12b, diagram f) initiates the automatic station finding operation as described.
In the embodiment of FIG. 3, the two series-connected parallel memories 15 and 16 are incorporated on the chip of an integrated-circuit module 25 which also comprises the circulating digital counter 7 and, for example, the circuit 26 of a station memory device. The station memory device has the memory inputs D ₁ to D _n and the memory outputs Y ₁ to Y _n of its circuit 26 connected in parallel with the digital counter 7 in the same manner as the recall memory consisting of the two series-connected parallel memories 15 and 16. Therefore, gate circuits 27 and 28 are inserted between the parallel outputs of these memories and the parallel inputs A ₁ to A _n of the digital counter. The gate circuit 27 between the recall memory and the counter is opened by the set signal of the recall switch 19. The gate circuit 28 between the station memory and the counter is opened by the set signal of a switch 29 for calling the bit word of a station preselected by the station buttons 30. In front of the set input 8 of the digital counter the two set signals are separated from one another in an OR circuit 31.
In the embodiment of FIG. 3, the start-stop circuit 10 is designed in the manner of a flip-flop and can assume a "stop" state and an "automatic station finding" state. The transfer inputs S of the recall memory's parallel memories 15 and 16 are connected via the lines 32 and 33 to the outputs of the start-stop circuit. Since the signals at the outputs of the start-stop circuit are continuous signals, the lines 32 and 33 to the transfer inputs include pulse shapers 34 and 35, respectively.
In embodiments corresponding to FIG. 3 and having no station memory device, besides the circuit 26, the gate circuits 27 and 28 and the OR circuit 31 are omitted.

An automatic fine tuning (AFT) circuit is provided which generates an AFT control signal in response to a video intermediate frequency (I.F.) signal. The I.F. signal is supplied to the inputs of two buffer amplifiers, which couple signals of like phase relationship to two inputs of a discriminator network. The discriminator network is tuned to the desired frequency of the video I.F. signal, and is responsive to the buffered I.F. signals for causing respective signal voltages to be developed at its inputs which vary differentially in magnitude in response to the frequency deviation of the I.F. signals from the desired I.F. frequency. The differentially related signals are detected by two peak detector networks for use as AFT control signals. The buffer amplifiers and peak detectors may be conveniently fabricated on a single I.C. chip. The discriminator network is coupled to the buffer amplifiers by two external I.C. terminals.

1. In an automatic fine tuning circuit including an integrated circuit chip having first and second contact areas for coupling to discrete circuit elements located external to said integrated circuit chip, apparatus comprising:

means located on said integrated circuit chip for supplying input signals having a frequency within a band including a predetermined reference frequency to said first and second contact areas;

a discriminator network, located external to said integrated circuit chip and coupled to said first and second contact areas, and responsive to said input signals for providing respective signals at said first and second contact areas which vary differentially in magnitude in response to the frequency deviation of said input signals from said reference frequency; and

first and second detector networks located on said integrated circuit chip and having respective input terminals direct current coupled to said first and second contact areas for detecting the magnitudes of said differentially varying signals.

2. In a television receiver, including a source of tuning voltage, and a tuner, including a reactive element responsive to said tuning voltage and an automatic frequency control signal, for producing a mixing signal to convert radio frequency television signals to intermediate frequency television signals within a band including a predetermined reference frequency, an automatic frequency control signal generator comprising:

first and second amplifiers, each having an input terminal for receiving a common intermediate frequency television signal having a frequency within a band including said predetermined reference frequency and an output terminal; said amplifiers supplying respective signal currents of like phase relationship to said output terminals in response to said common input signal;

a discriminator network coupled to said output terminals of said first and second amplifiers for causing respective signal voltages developed at said output terminals of said first and second amplifiers to vary differentially in magnitude in response to the frequency deviation of said intermediate frequency television signal from said reference frequency;

first and second detector networks respectively coupled to said output terminals of said first and second amplifiers for detecting the magnitudes of said differentially varying signal voltages;

a differential amplifier for developing output signals which vary differentially in sense and magnitude in response to the magnitudes of the signals detected by said first and second detector networks; and

means coupled to said differential amplifier for combining said output signals to develop an automatic frequency control signal which varies in sense and magnitude in response to the frequency deviation of said intermediate frequency signal from said predetermined reference frequency,

wherein said amplifiers, said detector networks, said differential amplifier, and said combining means and couplings therebetween are realized in integrated circuit form on a common monolithic integrated circuit chip, wherein each of said output terminals comprises an external connection terminal of said integrated circuit chip, wherein said discriminator network comprises components separate from said chip and coupled to said chip terminals, and wherein said automatic frequency control signal is coupled to said reactive element at a third chip terminal to control the frequency of said mixing signal.

3. The automatic frequency control signal generator of claim 2, further comprising:

a controllable current source having an input responsive to said tuning voltage and having an output coupled to said differential amplifier for varying the magnitude of the sum of said output signals for a given deviation of said intermediate frequency signals from said reference frequency, wherein said current source is located on said integrated circuit chip and said input is coupled to a fourth chip terminal to receive said tuning voltage.

4. In an automatic frequency control signal circuit including an integrated circuit chip having first, second and third contact areas for coupling to discrete circuit elements located external to said integrated circuit chip, apparatus comprising:

means located on said integrated circuit chip for supplying input signals having a frequency within a band including a predetermined reference frequency to said first and second contact areas;

a discriminator network, located external to said integrated circuit chip and coupled to said first and second contact areas, and responsive to said input signals for providing respective signals at said first and second contact areas which vary differentially in magnitude in response to the frequency deviation of said input signals from said reference frequency;

first and second detector networks located on said integrated circuit chip and having respective input terminals coupled to said first and second contact areas for detecting the magnitudes of said differentially varying signals;

a differential amplifier located on said integrated circuit chip and coupled to said detector networks for developing output signals which vary differentially in sense and magnitude in response to the detected magnitudes of said differentially varying signals; and

means located or said integrated circuit chip and coupled to said differential amplifier for combining said output signals to develop an automatic frequency control signal at said third contact area which varies in sense and magnitude in response to the frequency deviation of said input signals from said predetermined reference frequency.

5. The automatic frequency control signal circuit of claim 4, further comprising:

a controllable current source located on said integrated circuit chip and having an input coupled to a fourth contact area and an output coupled to said differential amplifier; and

means external to said integrated circuit chip and coupled to said fourth contact area for varying the magnitude of the sum of said output signals for a given deviation of said input signals from said predetermined reference frequency.

6. Frequency discriminating apparatus comprising:

means for supplying input signals having a frequency within a band including a predetermined reference frequency;

a discriminator network, coupled to said input signal means, which provides respective signals which vary differentially in magnitude in response to the frequency deviation of said input signals from said reference frequency;

means for detecting the respective magnitudes of said discriminator network signals;

an amplifier coupled to said detecting means for developing first and second output currents respectively representative of said respective signal magnitudes;

means for combining said first and second output currents to develop a difference current which is related in sense and magnitude to the frequency deviation of said input signals from said reference frequency; and

a controllable current source coupled to said amplifier for controlling the magnitude of the sum of said first and second output currents for a given frequency deviation of said input signals from said reference frequency.

7. Frequency discriminating apparatus comprising:

means for supplying input signals having a frequency within a band including a predetermined reference frequency;

a discriminator network, coupled to said input signal means, which provides respective signals which vary differentially in magnitude in response to the frequency deviation of said input signals from said reference frequency;

means for detecting the respective magnitudes of said discriminator network signals;

an amplifier coupled to said detecting means for developing first and second output currents respectively representative of said respective signal magnitudes;

means for combining said first and second output currents to develop a difference current which is related in sense and magnitude to the frequency deviation of said input signals from said reference frequency; and

first and second transistors each disposed in a common base amplifier configuration to receive one of said respective output currents from said amplifier and having respective output electrodes coupled to said current combining means.

8. Frequency discriminating apparatus comprising:

means for supplying input signals having a frequency within a band including a predetermined reference frequency;

first and second terminals;

first and second transistors each having an input electrode coupled to said input signal supplying means and respective output electrodes coupled to said first and second terminals for supplying signals of like phase relationship at said terminals;

a discriminator network coupled to said first and second terminals for causing the signals developed at said first and second terminals to vary differentially in magnitude in response to the frequency deviation of said input signals from said reference frequency;

means for detecting the magnitudes of said differentially varying signals; and

a differential amplifier responsive to the detected magnitudes of said differentially varying signals for developing an output signal which varies in sense and magnitude in response to the frequency deviation of said input signals from said reference frequency,

wherein said discriminator network is tuned to said reference frequency and comprises:

a first parallel combination of a capacitor and an intermediate tapped inductor, coupled between said first and second terminals; and

a second parallel combination of a capacitor and an inductor, coupled between said intermediate tap of said inductor of said first parallel combination, and a source of supply voltage.

9. In a television receiver, automatic frequency control apparatus for providing an automatic frequency control signal which varies in response to the frequency deviation of an intermediate frequency signal from a predetermined reference frequency, comprising:

means responsive to said intermediate frequency signal for providing first and second input signals of like phase relationship;

a discriminator network, coupled to said input signal means, and responsive to said first and second input signals, for causing said input signals to vary differentially in magnitude in response to the frequency deviation of said input signals from said reference frequency;

means coupled to the junction of said input signal means and said discriminator network for detecting the magnitudes of said differentially varying signals;

a differential amplifier coupled to said detecting means for developing output signals which vary in sense and magnitude in response to the detected magnitudes of said differentially varying signals; and

a current mirror circuit coupled to said differential amplifier for combining said output signals to develop an automatic frequency control signal which varies in sense and magnitude in response to the frequency deviation of said intermediate frequency signal from said predetermined reference frequency, wherein said automatic frequency control signal may be used to control the frequency of said intermediate frequency signal.

10. The automatic frequency control apparatus of claim 9, further comprising:

a controllable current source coupled to said differential amplifier and having an input for controlling the magnitude of the sum of the output signals developed by said differential amplifier for a given deviation of said intermediate frequency signal from said reference frequency.

11. In a television receiver, including a source of tuning voltage, and a tuner, including a reactive element responsive to said tuning voltage and an automatic frequency control signal, for producing a mixing signal to convert radio frequency television signals to intermediate frequency television signals within a band including a predetermined reference frequency, an automatic frequency control signal generator comprising:

means responsive to said intermediate frequency signals for developing signals which vary differentially in magnitude in response to the frequency deviation of said intermediate frequency signals from said reference frequency;

a differential amplifier for developing output signals which vary differentially in sense and magnitude in response to the magnitudes of the signals developed by said differential signal means; and

means coupled to said differential amplifier for combining said output signals to develop an automatic frequency control signal which varies in sense and magnitude in response to the frequency deviation of said intermediate frequency signal from said predetermined reference frequency, wherein said automatic frequency control signal is coupled to said reactive element to control the frequency of said mixing signal.

12. The automatic frequency control signal generator of claim 11, further comprising:

a controllable current source responsive to said tuning voltage and having an output coupled to said differential amplifier for varying the magnitude of the sum of said output signals for a given deviation of said intermediate frequency signals from said reference frequency.

Description:

This invention relates to automatic frequency control apparatus in general, and, in particular, to such apparatus for deriving a frequency dependent error-correction signal to control the tuning of a local oscillator in a superheterodyne receiver.

It is the function of a television tuner to select a narrow range of frequencies from among the many broadcast frequencies in the radio frequency band. A conventional television tuner performs this function through the use of a radio frequency amplifier, a mixer, and a local heterodyne oscillator. The output of this oscillator is compared to, or beat with, the radio frequency television signal received from the receiver antenna by the mixer. This beating action creates both the sum and difference frequencies of the original radio frequency and local oscillator frequencies. All but the difference frequencies, called intermediate frequencies (I.F.), are filtered out. These I.F. frequencies are amplified and detected by the television receiver to recreate the desired sound and picture information.

In order to provide the optimum image on the television screen, together with accurate sound reproduction, it is necessary that the receiver local oscillator be adjusted so that the picture and sound carriers are located at the correct points in the I.F. passband of the television receiver. This is especially true in the tuning of color television receivers. Not only must the picture and sound carriers be situated at their proper positions in the I.F. passband but the color subcarrier must also be properly positioned in order that the colors will be reproduced by the kinescope with proper hue and saturation characteristics. If the local oscillator is for any reason not set at the proper frequency, the intermediate frequencies will be incorrect, and may deleteriously affect the reproduced sound and picture. As is well known, this mistuning may be due to improper fine tuning by the television viewer, local oscillator drift, or inaccurate resetability of the detenting action of a mechanical tuner. In order to overcome these problems, conventional receivers are provided with means for compensating for variations in the intermediate frequencies.

This compensation is normally accomplished by deriving an automatic fine tuning (AFT) voltage from the output of the I.F. amplifying stage of the receiver. The AFT voltage is representative of the sense and degree that the I.F. signal departs from the desired I.F. signal. The AFT voltage is applied to a voltage responsive reactance device in the local oscillator to correct the mistuning of the oscillator and thereby optimize the sound and picture reproduction.

There are presently two types of AFT circuits in general use: the quadrature detector type and the differential envelope detector type. The quadrature detector type AFT circuit converts frequency shifts of a frequency modulated signal to differentially phase-shifted signals by applying the frequency modulated signal to a filter network, which develops two differentially phase-shifted, or delayed, signals at its output ports. The differentially phase-shifted signals are coupled to a quadrature, or phase, detector, which converts the relative phase difference between the signals at the filter output ports to an amplitude-varying AFT control signal. The differential envelope detector type AFT circuit, such as that described in the present application, utilizes a linear filter network to convert frequency shifts of a frequency modulated signal to differentially related, amplitude varying signals. These signals are coupled to envelope detectors, which convert the amplitude varying signals to AFT control signals. The differential envelope detector AFT circuit generally requires fewer components than the quadrature detector type, and is preferred in many applications because of its ability to produce a narrower, more precisely controlled AFT bandwidth. The narrower bandwidth reduces the effect of I.F. noise on the AFT control system and produces sharper AFT response in the vicinity of the I.F. picture carrier being controlled by the system.

In order to minimize the size and number of components required to construct an AFT circuit, it is desirable to fabricate the circuit in integrated circuit form on a single monolithic integrated circuit chip. However, certain AFT circuit elements, specifically, the reactive components used to construct the discriminator network necessary to convert frequency shifts of the I.F. signal to amplitude modulated signals, do not readily lend themselves to integrated circuit fabrication and must be located external to the I.C. chip. The I.C. chip has only a limited number of external connection points, or terminals, for connection to external components. Hence, it is desirable to construct the AFT circuit in a manner which reduces the number of required connections to external components.

In accordance with the principles of the present invention, an AFT circuit is provided which generates AFT control signals in response to a video I.F. signal. The I.F. signal is supplied to the inputs of two buffer amplifiers, which couple parallel signals of like phase relationship to two inputs of a discriminator network. The discriminator network is tuned to the desired I.F. frequency, and is responsive to the buffered I.F. signals for providing respective signals at its inputs which vary differentially in sense and degree with the frequency deviation of the buffered I.F. signals from the desired I.F. frequency. The differentially related signals are detected by two peak detector networks for use as AFT control signals. The buffer amplifiers and peak detector networks may be conveniently fabricated on a single I.C. chip. The discriminator network is coupled to the buffer amplifiers and peak detectors through two external I.C. terminals.

The peak detected signals may be combined and amplified to produce an AFT signal for application to the local oscillator. However, a circuit with an AFT signal which varies over a fixed voltage range is restricted to operation with local oscillators which respond to the specific voltage range of that circuit. Such an AFT circuit can be used with a wide variety of local oscillators of differing characteristics only if additional interfacing circuitry is interposed between the AFT circuit and the local oscillator. Such interfacing circuitry can add undesirable delays and complexity to the AFT system.

In accordance with a further aspect of the present invention, the detected, differentially related signals are combined by a differential amplifier and coupled to a current mirror circuit to provide an AFT current signal. The current mirror circuit is contained on the same I.C. chip as the buffer amplifiers and detector networks. Through the use of a suitable external load resistor, the AFT current signal may be used to produce a wide variety of AFT voltage ranges. In addition, means are provided for varying the magnitude of the AFT current signal to permit accurate matching of the AFT circuit to the signal requirements of the local oscillator. The magnitude of the AFT current signal may be modified during operation of the television receiver, for example, to provide continuously variable AFT current signal ranges over the full range of television channels.

SELECO (ZANUSSI) 20ST211 BRAVO 20"  CHASSIS BS465.2  Two-speed searching television tuner:
 A television tuning device having a circuit for continuously scanning at least one frequency band. Scanning can take place at two speeds and controls are provided for starting and stopping the scanning procedure. The scanning speed is automatically changed from high speed to low speed when a television channel is detected to allow ample time for scanning to be stopped manually. Alternatively, the scanning may be stopped automatically.

1. A television tuning device comprising a circuit scanning means for continuously scanning at least one band of receivable frequencies, manual control means for starting and stopping said scanning, a terminal means for applying a switch signal to said scanning means for switching from a first band-scanning speed to a second band-scanning speed lower than the first, and detection means for detecting the presence of a television channel by comparing received synchronization signals with local signals generated in the television receiver and for applying a switch signal to said terminal means for switching from said first band-scanning speed to said second band-scanning speed in the presence of said switch signal so that the band scanning continues at said second band-scanning speed until the manual control means stops the scanning.

2. A television tuning device according to claim 1, further comprising scanning stopping means for stopping the scanning automatically when a television channel has been correctly tuned in, speed reducing means for reducing band-scanning speed, and said detection means comprising first and second detecting means for detecting the presence of a television channel which act in sequence one after another for supplying to said speed reducing means control signals at successive instants so as to increase the effective time interval during which said scanning stopping means may operate.

3. A device according to claim 2, further comprising controlling means for controlling the tuning frequency of the receiver automatically for optimum tuning, said controlling means being activated or de-activated by said switch signal provided by the said detection means for detecting the presence of a television channel.

4. A device according to claim 1, in which said band-scanning circuit means includes means for generating scanning signals at increasing speed starting from the instant scanning commences, and means for stopping and restarting scanning when the presence of a television channel is detected so that scanning continues at the same speed as when it commenced.

5. A device according to claim 1, in which said detecting means includes a coincidence detector means for detecting coincidence between the synchronization signals received and picture tube deflection signals generated inside the television receiver.

6. A device according to claim 1, in which said manual control means includes two push-buttons, one for controlling commencement of band scanning from the lowest to the highest frequencies and the other for controlling commencement of band scanning in the opposite direction and in which scanning commences on pressing one of said buttons and stops upon release of the same button.

7. A device according to claim 3, in which said first detecting means for detecting the presence of a television channel includes a detector means for detecting coincidence between the synchronization signals of the received signal and picture tube deflection signals generated in the television receiver and said second detecting means includes a threshold comparator means for receiving the output signal of said controlling means and processing means for supplying by means of processing means a signal for stopping band scanning.

8. A device according to claim 7, in which said processing means are operative to supply a signal for restarting band scanning at the same speed at which it was commenced.

9. A device according to claim 7, in which said processing means includes a series circuit comprising a disabling circuit which receives the output signals of said first and second detecting means, a Flip Flop, and an exclusive OR logic circuit, which stop the scanning operation and prevent it from being continued until a new scanning-start signal is received from said controlling means and such as to reset the Flip Flop.

10. A device according to claim 9, further comprising means for resetting said series circuit when the receiver is turned on to prevent scanning from being commenced until the scanning-start signal is sent.

Description:

The present invention relates to a television tuning device, comprising a circuit for continuously scanning at least one band of receivable frequencies, and having control means for starting and stopping the said scanning procedure and a terminal for applying a switch signal for switching from a first band-scanning speed to a second band-scanning speed slower than the first.
The name usually applied to a unit consisting of circuits of this type for selecting and memorising a given number of preferred channels is "station memory".
Many types of station memories are already being sold on the market which can be divided into two main groups: those with automatic and those with manual television channel searching.
The automatic types are fitted with electronic searching circuits which locate television channels automatically when started by the user. This is done by scanning a given band (VHF or UHF, for example) and stopping on the located channel. Data relative to the located channel can then be memorised by the user in a memory circuit and the same channel recalled whenever required by simply pressing a button which recalls the said data from the memory and supplies it to the channel selection circuit.
This type of circuit is also fitted with components which sense, during search, if a television channel has been tuned into and disable automatic searching to prevent television band scanning from continuing. Most of these circuits are fitted with a phase detector which senses the coincidence between the sync signals received and those regenerated in the receiver (in particular, the flyback signal).
Manual station memories, on the other hand, are fitted with controls which, when activated by the user, start a device for scanning a given television band. These controls also stop the said device when required by the user. When the user sees the required channel appear on the screen, the device is stopped to disable search and enable the channel to be memorised in the appropriate circuit.
In these cases, the simplest way of starting and stopping the search is to fit the circuits with a button which, when pressed, supplies a search-start signal and, when released, stops the searching operation. For best tuning, two buttons are usually provided for band scanning in both directions.
Both the types discussed up to now present drawbacks. In the case of automatic station memories, for example, tuning quality depends on correct operation of all the search-stop circuits and the automatic tuning circuit (AFC=automatic frequency control). Even in cases where these circuits are operating correctly, tuning could still be impaired by noise or amplitude distortion on the received signal.
Tuning quality on manual station memories, on the other hand, depends on the tuning ability of the user. Television receivers can be manipulated by anybody not all of whom are gifted with this ability. A further drawback of manual station memories is that the user has very little time in which to decide whether the received channel is the right one and to estimate tuning quality. If the whole television band is to be scanned in a reasonable length of time (let us say, the UHF band in one minute) band-scanning speed needs to be fairly high. Consequently, if the user is not quick enough in sending out the search-stop control signal, it is more than likely that the control will be sent when the required television channel has been overshot. If, by chance, there are two channels close to one another, the searching device may even stop on the second of the two, thus confusing the user who will not know which of the two channels he has tuned into.
The aim of the present invention is to provide a tuning device to overcome these problems.
With this aim in view, the present invention provides a television tuning device comprising a circuit for continuously scanning at least one band of receivable frequencies, manual control means for starting and stopping the said scanning procedure, a terminal for applying a switch signal for switching from a first band-scanning speed to a second band-scanning speed lower than the first, and detection means for detecting the presence of a television channel by comparing the received sync signals with local signals generated in the television receiver, and applying a switch signal to the said terminal for switching from the said first scanning speed to the said second scanning speed in the presence of the said switch signal, so that the band scanning continues at said lower speed until the manual control means produce the stopping scanning procedure.

BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 shows a block and circuit diagram of an exemplary television tuning device according to the invention; and
FIG. 2 shows the internal structure of exemplary integrated circuits used in the diagram of FIG. 1.
In the diagram, an input terminal receives an input signal from a frequency discriminating circuit, which forms part of a known automatic frequency control (AFC) circuit, the input signal being applied to a known Schmitt trigger circuit, generally designated 2. The output of circuit 2 is connected to a first input of a ci

rcuit 3 which has two outputs, one connected to set input S and one to reset input R of Flip Flop circuit 4. Input S of the said Flip Flop is also connected to a first input of an exclusive OR logic circuit 5 and a first output of a control circuit 6 which has a second output connected to input R of circuit 4 and an input connected to a terminal of a first push-button 7 the other terminal of which is grounded.
Number 8 represents an input for receiving line sync signals obtained in the known way from sync separating circuits, the signals being applied to a first input of a coincidence detecting circuit 10 the second input of which is connected to receive a line flyback pulse 9, obtained from the horizontal deflection circuits. The output of circuit 10 is connected to a signal translation circuit 11, the second input of circuit 3 and an output 12 which can be sent to activate the AFC circuits on the set. ON reset circuit 13 has a first output connected to the second input of circuit 5, which is also connected to the output of circuit 4 through disconnecting resistor 22, and a second output connected to the control input of circuit 3, which is also connected to the output of circuit 5 through resistor 14. The output of EX-OR circuit 5 is also connected to the input of matching stage 15 the output of which is connected to a second push-button 16 and a first control input (UP) of a tuning detection and memorising circuit 17. This has a second control (down) input connected to a third push-button 18. A detection speed switch input is connected to the output of circuit 11. Input 21 can be connected, in the known way, to a station keyboard, outputs 19 and 20 representing respectively the tuning voltage to be sent to the tuning circuit and the channel indication to be sent to an appropriate display, using known methods. Push-buttons 16 and 18 are the same as push-button 7 and therefore have their second terminals grounded.
The known station memory circuit 17 consists mainly of TEXAS INSTRUMENTS Ser. No. 76,720 and Ser. No. 76,727 integrated circuits, an amplifying transistor, a filter and passive components for piloting the said integrated circuits as recommended by the makers. Push-buttons 16 and 18 are connected to terminals 10 and 11 of integrated circuit Ser. No. 76,720 respectively. Input 21 is represented by terminals, 1, 15, 16, 17 and 18 of the same integrated circuit while terminal 13 is connected directly to the output of circuit 11. The components used for performing the required function are represented inside a number of the circuits already mentioned. The ratings of the resistors and condensers are shown directly in the diagram. The ratings of the remaining components are as shown in the Table below:

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NPN transistors BC 148B PNP transistors BC 158B Diodes 1N4148 NOR gates 1/4 F4001 (+ A supply) NAND gates 1/4 F4011 (+ A supply) + A 5V + B 12.5V + C 33V

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The circuit operates as follows:
When one of the buttons on the television panel connected to inputs 21 of circuit 17 is pressed, the corresponding memory register in circuit 17 (I.C. Ser. No. 76,720) is activated to give a voltage at output 19 corresponding to the tuning voltage of a given television channel memorised previously. If a video signal is present, the horizontal deflection circuits on the set are synchronized by the sync signals in the received signal, coincidence detector circuit 10 supplies a high output voltage so that the AFC circuit comes into operation, controlled by output 12 for optimum tuning. In this case, the voltage at the output of stage 15 is high and circuit 17 undertakes no further operations to detect other emitting stations. The voltage at the output of EX-OR stage 5 is also high so that the circuit at gate 3 is kept closed, a situation which persists until one of the control buttons is pressed. By pressing other keys on the board, it is possible to tune into other stations memorised previously in the same way as described already. If there is no television signal present for the key pressed, circuit 10 detects no coincidence, its output remains low and the AFC circuit does not come into operation.
A second operation mode is possible by which a new emitting station can be searched manually using push-buttons 16 and 18. Keeping button 16 pressed, for example, station memory circuit 17 detects towards the higher frequency channels at increasing speed. Integrated circuit Ser. No. 76,720 has two different search speeds (one for VHF and one for UHF channels, for example). On the circuit referred to in the present invention, searching speed is determined by coincidence detector 10. If no coincidence is detected, that is if the search is performed in a frequency zone with no stations, the voltage at the output of circuit 10 and, consequently, also at the output of circuit 11 will be low so that searching is made at maximum speed. If a station is approached, however, circuit 10 switches so that a speed switch signal is sent to terminal 13 of integrated circuit Ser. No. 76,720. Operation of the integrated circuit is such that the search is continued at the minimum speed allowed by the system. This simplifies the tuning operation by allowing the user much more time than he would have had with the original station memory circuit 17. At the same time, no advantage is lost in terms of scanning speed over empty bands. In fact, this is always performed at maximum speed even over UHF bands. Optimum searching can be made by pressing buttons 16 and 18 alternately; this condition is automatically registered in the memory by integrated circuit Ser. No. 76,720.
A third mode of operation is possible in which searching and memorising are performed automatically. When button 7 is pressed, low and high voltages are applied, through circuit 6, to the set and reset inputs of Flip Flop 4 respectively so as to force the output to zero. Two zeroes are thus applied to EX-OR circuit 5 so as to create a low voltage at its output. In this way, the voltage at the output of circuit 15 moves to zero and circuit 17 starts searching upwards exactly in the same way as when button 16 was pressed. After a given interval, determined by resistor 14 and the condenser at the control input of circuit 3, this gate circuit opens so that the signals at its inputs can be sent to the inputs of Flip Flop 4. During the search, in the absence of any stations, the output of circuit 10 is low while that of trigger circuit 2 is high. This results in a 1 at the reset input and a 0 at the set input of the Flip Flop so that the output of circuit 15 remains low and the search is continued. As soon as a station is approached, on the video carrier side, given the searching direction chosen, the horizontal deflection circuits are synchronized with the signal, the coincidence detector supplies a high output and the AFT circuits become activated through output 12 to reduce searching speed (circuits 11 and 17).
The reset input of the Flip Flop moves to zero but the output remains unchanged and the search continues at low speed. Over time, the AFC voltage at input 1 describes a curve in the form of an S, that is it starts at zero, rises to a maximum, returns to zero (optimum tuning), reaches a minimum and then returns to zero.
When the threshold of trigger 2 is reached, the latter switches, that is, its output becomes low, Flip Flop inputs S and R become 1 and 0 and switching commences. For a time period equal to the delay of the Flip Flop, a 1-0 condition exists at the input of the EX-OR circuit so that its output presents a positive peak which stops searching for an instant. After the Flip Flop switches (high output) a 1-1 condition exists at the EX OR input so that the output becomes low and searching continues at minimum speed. When the falling AFC voltage crosses the trigger threshold again, the trigger output becomes high causing it to switch. Two zeroes are present at the Flip Flop input, therefore its output remains at 1 with a 1 and 0 at the EX OR input. The result is its output becomes high, searching is stopped on the required station and this tuning condition memorised automatically in circuit 17. Following the delay determined by resistor 14, gate circuit 3 closes and the tuning condition reached can no longer be disturbed. For searching to be continued, button 7 must be pressed after which the cycle is repeated in the same way.
To prevent the searching process being started up automatically during the transients when the receiver is turned on, in addition to the pre-biasing resistors at the NOR gate inputs of circuit 3 and the input of stage 15, circuit 13 is provided which, for a given time, depending on the delay introduced by the RC network connected to +E voltage, applies a high voltage to the EX OR circuit input and the control input of gate 3 so as to keep it disabled. Also, as Flip Flop 4 consists of two twin-input negative-feedback NOR gates, the logic 1 applied by the reset circuit to the EX OR input and then to the Flip Flop output is returned to the input of one of the NOR gates so as to set the Flip Flop at 1.
FIG. 2 show

s the details of the integrated circuits used in the circuit of FIG. 1. The I.C. type Ser. No. 76,727 provides a clock signal to the other I.C. Ser. No. 76,720. This circuit features an oscillator which is controlled by an external crystal coupled to pins 2 and 3. A pair of cascaded divide-by-two flip-flops provide the proper clock signal at pin 4. A D-type flip-flop, which provides waveform shaping, is coupled to pin 4, and has both Q and Q output signals applied to pins 13 and 14 respectively. Two additional cascaded divide-by-two flip-flops are coupled to the Q output of the D-type flipflop and provide buffered output signals on pins 6 and 9 for driving a LED display (not shown). Two keyboard scanning output signals are provided at pins 5 and 10 which are in synchronization with the LED output signals at pins 6 and 9 but are narrowed and delayed to avoid edge coincidence glitches.
The station memory is Texas Instrument integrated circuit of the type Ser. No. 76,720 which receives the clock signal at its pin 9 and applies it to 12 bit synchronous counter. Pins 15 to 18 and 1 correspond to the input terminal 21 of the present invention and are intended to carry a five bit code identifying the manually selected channel. The signals are applied to 5 to 20 line decoder which in turn applies signals to a 12 bit tuning voltage RAM. The pins 10 and 11 are the up and down frequency scanning controls shown in FIG. 1 and the VHF/UHF pin 13 is also scanning speed controlled. The scanning is effected by transferring the data of the prevailing channel into the transparent counter and modifying this data under the control of the tuning program generator, the counter being clocked up or down at rate determined by the tuning timer and the countdown frequency select circuit. When one or the other buttons connected to the pins 10 and 11 is depressed, the count is incremented initially at a slower rate, the rate increasing gradually until it reaches a miximum level determined by the signal applied to pin 13.
The advantages of the circuit according to the present invention will be clear from the description given. First and foremost, as compared with known solutions, is the extra time allowed to the user for stopping the search when this is done manually. This is possible with no increase in the time taken for a complete band to be scanned. A further advantage is the possibility of two types of search: automatic and manual. The advantages of both operating modes are thus combined in one device to provide the best results. In particularly delicate cases, the user can leave aside automatic searching and perform the operation manually. A further advantage is that, when operating automatically the circuit described is provided with two circuits which, as optimum tuning is approached, both slow down band-scanning speed one after the other to facilitate operation of the automatic searching-stop 2/3 circuit and recognition of correct tuning. One last advantage is that the arrangement described is particularly simple and economical considering the functions it performs. To those skilled in the art it will be clear that variations can be made to the circuit described without, however, departing from the scope of the present invention as defined in the claims. Of these we shall mention just a few. For example, the possibility of using only one type of search, e.g. manual. Another variation could be to use a different type of station memory, for example another of the "dedicated" integrated circuits available on the market or a station memory circuit made using a microprocessor. It should be pointed out that the circuits shown in the blocks on the diagram are only a few of the many types capable of performing the functions required and that numerous variations can be made to them.

SELECO (ZANUSSI) 20ST211 BRAVO 20"  CHASSIS BS465.2  Infrared telecommand receiver:

  1. A telecommand receiver comprising a photodiode for receiving a signal emitted by a transmitter in the form of a train of amplitude-modulated infrared radiation with two suitably alternating frequencies B1 and B2, an amplifier stage, a peak detector circuit, and an integrator stage adapted to control a comparator, characterized in that downstream of said amplifier stage (15) there is provided an attenuator circuit (22 26), followed by a controlled-gain amplifier (27) in combination with a discriminator filter (28 - 31).

2. A telecommand receiver according to claim 1, characterized in that the output of said integrator stage (37, 38) is directly connected to one input of said comparator (42), and is further connected to the other input of said comparator through a further integrator stage (39, 40).

3. A telecommand receiver according to claim 1, characterized in that said discriminator filter (28 - 31) associated with said controlled-gain amplifier (27) is attuned to one of said frequencies (Fl, F2).

4. A telecommand receiver according to claim 1, characterized in that a maximum-gain amplifier (20) is interposed between said amplifier stage (15) and said attenuator circuit (22-26).

Description:

Infrared Telecommand Receiver D e s c r i p t i o n  This invention relates to an improved infrared telecommand receiver particularly for controlling a television set.
As is generally known, telecommand systems of this type are adapted to emit and receive signals in the form of infrared rays, the amplitude of which is modulated, usually in accordance with the so-called FSK system, with two different frequencies alternating in a suitable manner in accordance with the command signal to be transmitted. These frequencies are usually designated B1 (41.6:kc) and F2 (50 kc).
A receiver for receiving telecommand signals of this type usually comprises a phase-locked loop circuit adapted to convert the received telecommand signal into a corresponding pulse train for controlling a microprocessor which is provided in the apparatus to be remotely controlled, and which is only able to receive digital signals at its input, as generally known.
The phase-locked loop circuit is particularly suitable for converting the received command signals into a digital code, its adjustment is very critical, however, detracting thus from reliability of operation.
It is therefore an object of the present invention to provide an infrared telecommand receiver which does not require any adjustment while still being of simple construction and reliably accurate operation.
The invention thus provides an infrared telecommand receiver comprising a photodiode for receiving a signal emitted by a transmitter device in the form of an ampli tude-modulated train of infrared rays with two suitably alternating frequencies F1 and F2, an amplification stage, a peak indicator circuit and an integrating stage adapted to control a comparator circuit.
According to the invention, a receiver of this type is characterized in that downstream of the amplification stage there is provided a limiter circuit followed by a controlled-gain amplifyer provided with a discriminating filter.
These and other characteristics of the invention will become evident from the following description of an exemplary embodiment with reference to the accompanying drawings, wherein: fig. I shows a circuit diagram of a receiver in a pre ferried embodiment of the invention, and fig. 2 to 9 show the shape of signals appearing at significant points of the circuit shown in fig. 1.
The receiver according to the invention comprises a photodiode 10, connected as shown in fig. 1, for receiv- ing signals enitted by a transmitter in a per se known manner. These signals are in tbe form of a train of infrared rays, the amplitude of which is modulated according to the FSK system, with two different frequencies Fl and B2 alternating in accordance with the commands to be transmitted.
Photodiode 10 is connected to a load resistor 11 and, through a neutralizing capacitor 12, to a resistive voltage devider 13, 14.

The signal received by photodiode 10 (Fig. 2) is applied to a controlled-gain amplifyer 15 in the form of an alternating voltage with the frequencies Fl and F2.
This amplifier is connected to a selective filter formed of resistors 16 and 17 and capacitors 18 and 19 attuned to the frequency F1 so as to accentuate it.
The thus processed signal (Fig. 3) is applied to a maximum gain amplifier 20, the output of which is connected to a limiter circuit formed of diodes 22, 23 and a resistor 24. A capacitor 21 is employed in a per se known manner for reducing the gain of amplifier 20 at frequencies below F1 and F2.
The limiter circuit is associated with a voltage divider 25, 26 and cooperates therewith as an antisaturation attenuator limiting the amplitude of the signal (fig. 4) appearing at the output of amplifier 20 to a predetermined maximum level (Fig. 5) as a function of the dimensioning of the receiver.
This signal is applied to a further controlled-gain amplifier 27 corresponding to amplifier 15 and likewise provided with a discriminating filter constituted by resistors 28, 29 and capacitors 30, 31 attuned to the frequency Fl.
The amplifier-filter combination 27 - 31 is able to reliably differentiate the frequencies F1 and F2 of the signal, accentuating the frequency F1, thanks to the limited amplitude of the signal applied to its input, which prevents the amplifier itself from attaining the state of saturation.
This provision is of partucular importance, since, if the amplifier-filter combination 27 - 31 were to attain its state of saturation due to an input signal of excessively high amplitude (in the case, for instance, that the infrared command signal were received over a short distance and thus with an excessive amplitude), it would no longer be possible to discriminate between the two frequencies Fl and F2. As already said, this problem is overcome by the provision of the attenuator 22 - 26 upstream of the amplifier-filter combination 27 - 31.
The thus obtained signal (fig. 6) is subsequently processed by a peak detector circuit comprising a resistor 32, diodes 33, 34 and capacitors 35, 26, resulting in the signal shown in fig. 7.
The latter signal then passes through two cascade-connected integrators formed respectively of a resistor 37 and a capacitor 38, and a resistor 39 and a capacitor 40.
The output 41 of the first integrator is directly applied to the invertin input of a comparator 42 (differential amplifier), while the output 43 of the second integrator controls the non-inverting input of comparator 42.
The signal appearing at output 41 is represented by a continuous line in fig. 8, while the signal at output 43 is shown in broken lines in this figure.
The two signals are substantially identical, although output signal 43 is somewhat attenuated and delayed with respect to output signal 41 due to the effect of the second integrator.
The comparator 42 generates in a per se known manner an output signal in the form of a square wave (fig. 9) representing in digital form the information content of the infrared radiation signal received by photodiode 10.
The described solution thus permits the automatic compensation of the signal applied to comparator 42, as the two signals applied to the inputs of the comparator vary in an analogous manner, so that the relative difference between them is maintained substantially constant.
The circuit according to the invention is thus very simple and reliable, since there are no adjustments required as in the case of e phase-locked loop circuit.
The amplifiers 15, 20, 27 amd 42 are preferably combined in a single integrated circuit (for instance LS 404 by SGS). Otherwide, various modifications of the described embodiment are of course possible within the scope and spirit of the invention.