GB2152336A - Television receivers - Google Patents

Abstract

In a small, portable, battery operated television receiver having an electrostatically focussed and deflected cathode ray display tube, distortion of the display resulting from changes in the battery voltage as the battery becomes discharged are reduced by deriving all focusing and deflection voltages applied to the tube directly from the battery without stabilisation or regulation. The voltages for the tube are derived from the battery in such ways that they are proportional to the battery voltage and therefore the relationships between them are substantially maintained. The heater of the cathode ray tube may be supplied via a transformer energised by the battery voltage switched at line frequency and the line frequency pulses applied to the heater so as to cut off the beam during line flyback. The invention may be applied to cathode ray tube displays having sources other than a battery, whilst retaining the advantage of power saving resulting from the omission of voltage regulation circuitry.

Description

SPECIFICATION Television receivers This invention relates to television receivers.

Small, portable, battery-operated television receivers have been manufactured in the past but only recently has it become practicable to construct such receivers which are sufficiently small to be carried in a pocket, with the production of flat, cathode ray display tubes and other compact display devices. A disadvantage with a portable, battery-operated television receiver is that large batteries are heavy and are consequently undesirable, and lighter, smaller batteries do not have a large capacity, so that they have a short useful life and have to be replaced frequently, with an attendant cost penalty. It is therefore essential in such a receiver to keep the current consumption as low as possible.Partlyforthis reason and partly because of limitations of space it is desirable to include as many of the circuits of the receiver as conveniently possible in a single integrated circuit or possibly a few integrated circuits. A difficulty in the use of integrated circuits for processing signal waveforms such as are employed in television receivers arises because of the variations in the characteristics and the non-ideal behaviour of the elements of the circuits which need correction and/ or compensation for acceptable performance.

Another problem with battery-operated receivers is that the voltage produced by the battery falls during its useful life, so that regulation of the voltage is desirable for maintaining the required relationships between the various signals employed in producing the display, which otherwise could become distorted. Such regulation is, however, undesirable because of the power which is consumes.

It is therefore an object of the present invention to overcome one or more of the difficulties outlined above. It should, nevertheless, be borne in mind that the invention is applicable to any type of television receiver and not merely to portable, batteryoperated ones.

According to the present invention there is provided a television receiver having an electrostatically focussed and deflected cathode ray display tube in which all voltages applied to the tube are derived from the same unregulated supply voltage source without stabilisation or regulation in such a way that the display is substantially unaffected geometrically by changes in the supply voltage.

The invention provides also simplified line flyback blanking in that the cathode ray tube heater supply is connected to drive means controlled, in operation, by the line scan drive and the drive means is arranged to raise the voltage potential of the heater circuit during line flyback to cut off the cathode ray tube.

Preferably, the cathode ray tube heater drive means includes a supply transformer, and line-scan driven switch means controlling the energisation of the supply transformer, the junction point between the supply transformer and the switch means being connected to the cathode ray tube heater to communicate the voltage potential of the said junction point to the cathode ray tube heater.

Additionally, the invention provides field scan means which minimises power consumption being arranged, during flyback, to provide pull-up of the voltage potential of a scan capacitor through a resistor and to provide pull-down of the voltage potential of a complementary scan capacitor through a transistor.

The voltage source may be a battery of which the output voltage may be reduced by, for example, 10% over its useful life, and it may be that the only change in the display which would be evident to the viewer as the voltage falls is a reduction in its brightness.

In order that the invention may be fully understood and readily carried into effect, it will now be described with reference to the accompanying drawings, of which: FIGURE 1 shows a circuit diagram of one example of a television receiver according to the invention; and FIGURE 2 is a block diagram of the contents of the integrated circuit 9 of Figure 1.

Figure 1 shows the circuit diagram of one example of a television receiver using the invention.

The receiver has a flat electrostatically focussed and deflected cathode ray display tube 1 of the type described in British Patent Specification No.

1 592 571. The receiver is powered by a battery 2 providing 6 volts. The battery 2 is connected between an earthed conductor 3 and a supply conductor 4 to which it is connected by an on/off switch 5. The television signals are picked up by an aerial 6 which is connected to a tuner unit 7 which may be of conventional construction. The tuning of the unit 7 is effected by means of one or more varactor diodes to which an adjustable DC voltage is applied from a tuning potentiometer 8. The intermediate frequency output signal from the tuner unit 7 is applied to an integrated circuit 9, the details of which are shown in block diagrammatic form in Figure 2 and which contains the video and sound intermediate frequency, signal separation and processing circuits, detector and amplifier stages together with the sync signal separator and the line and field scanning oscillators.The sound output signal is reproduced by a loudspeaker 10, the volume of which is controlled by a potentiometer 11. The video output signal from the integrated circuit 9 is conveyed by a conductor 12 to a further video amplifer 13 consisting of two transistor stages, the output of which is connected to the grid of the cathode ray tube 1. The line scan signals are applied via a conductor 14 to the line scanning circuit 15 and also to a transistor 16 which operates as a switch to interrupt the DC supply to the primary of a transformer 7 which feeds pulses to produce a 15 volt supply for the video circuits on the line 12.The secondary winding of the transformer 17 supplied the energisation forthe heater of the cathode ray tube 1 and this is connected to the collector of the transistor 16so that the positive going pulses serve to blank the spot during line flyback. From the collector of the transistor 16 a supply voltage is derived which is established on a conductor 19 and is used to provide the tuning voltage of the tuner 7 via the potentiometer 8. A supply of 3 volts is set up on a supply conductor 20 by a part of the integrated circuit 9 to power the tuner unit 7. The field scan signal for the cathode ray tube 1 is supplied by the integrated circuit 9 via conductors 21 which are connected through a field scan amplifier 22 to the field scan electrodes of the cathode ray tube 1.

The line scanning circuit 15 receives the line drive signal supplied via the conductor 14 at the base of a transistor 23 which switches current through an autotransformer 24. The outputs from the autotransformer 24 on conductors 25 and 26 supply similar pulses of opposite polarities to switched integrators 27 and 28 respectively which generate saw-tooth waveforms with flybacks caused by the pulses on the conductors 25 and 26, the saw-tooth waveforms being conveyed via conductors 29 to the line signal deflection electrodes of the cathode ray tube 1. The autotransformer 24 also supplies high voltage pulses along a conductor 30 to supply the field amplifier 22 and further high voltage pulses on a conductor 31 for driving a diode-capacitor stack 32 which generates the various EHT voltages for the cathode ray tube 1.A further output from the integrated circuit 9 is fed along a conductor 33 to control the conductivity of a transistor 34 which determines the slopes of the flanks of the saw-teeth by regulating the current feed to the integrators.

This control is required because the cathode ray tube 1 is a flat tube with the screen end on to the electron gun.

The field amplifier 22 is arranged to drive the field deflection system of the cathode ray tube 1 through scan capacitors which must be reset to their respective starting potentials during the field flyback period. The resetting of the scan capacitors within the time allowed and with minimal power consumption is achieved by driving the capacitors differentially in such a sense asto provide pull-up of the voltage potential of one capacitor to its highvoltage potential start value by way of a resistor and to provide pull-down of the complementary capacitor to its low-voltage potential start value by way of its drive transistor.

Figure 2 shows a block diagram of the circuits contained in the integrated circuit 9 of Figure 1, and in Figure 2 the numbered terminals of the integrated circuit package are preceded by the letter T so that the first terminal is T1 and the last is T22. The output of the tuner 7 (Figure 1) is connected via terminal T19 to an intermediate frequency amplifier 100. The amplified output from the IF amplifier 100 is applied to a detector 101 and from that through a video amplifier 102 to the terminal T1 6. An AGC signal for the amplifier 100 is derived from the amplifier 102 by an AGC detector 103 from which the AGC signal amplified by amplifier 104 is applied to control the gain of the amplifier 100. A capacitor 105 external to the integrated circuit is connected via terminal T17 to the output of the detector 103 to smooth the gain control voltage.The intercarrier sound is picked off from the output of the video detector 101 and applied via a conductor 106 to a sound channel mixer 107. The oscillation from a local oscillator 108 is mixed with the sound signal from the output of the detector 101 to produce the required intermediate frequency signal which is amplified by IF amplifier 109, the amplified output of which is applied to a demodulator circuit 101 connected to apply the sound output signal to terminal T1 5. The potentiometer 11 serves as a volume control and regulates the amplitude of the audio signal reapplied to the integrated circuit at terminal T1 3 for amplification in the AF amplifier 111. The output audio signal is fed via the terminal T1 1 and a capacitor to the loudspeaker 10.

The video output signal from the amplifier 102 which appears at the terminal T16 is applied as described above with reference to Figure 1 to the grid of the cathode ray display tube 1. It is also reapplied to the integrated circuit via terminal T20 from which it is applied via a DC restoration circuit 112 to a sync separator circuit 113. Pulses at line frequency are conveyed by a conductor 114to a monostable multivibrator 115 and an IN LOCK detector 116. A picture element frequency oscillator 117 which has its frequency controlled by the output of a phase detector 118 applies pulses to a counter 119 of which the most significant bit output is fed via a conductor 120 to an input of the phase detector 118 which compares the time of arrival of the most significant bit with the output of the monostable 115.The output of the phase detector 118 also controls the frequency of the local oscillator 108.

When operating correctly the frequency of occurrence of the most significant bit signals on the conductor 120 will be at line frequency. The digital output of the counter 119 is applied to a line logic circuit 121, a line digital to analogue converter 122 and a correction digital to analogue converter 123.

The line logic circuit 121 produces a gate signal which is applied to the phase detector 118 through an INHIBIT circuit 124 for limiting the time period over which the phase detector 118 is effective near each most significant bito utput from the counter 119. The IN LOCK detector circuit 116 compares the timing of the line frequency pulses on the conductor 114 with the gate signals from the line logic circuit 121 on conductor 125 and is connected to the INHIBIT circuit 124to prevent the gate signals from being applied to the phase detector 118 unless the output of the line counter 119 is substantially synchronised with the signals from the monostable 115. The line logic circuit 121 output on the conductor 125 is also applied to the INHIBIT circuit 124. The line logic circuit 121 produces another output on the conductor 126 which is applied to an EHT INHIBIT circuit 127 connected to terminal T6 of the integrated circuit. This part of the circuit functions to inhibit the generation of pulses at line frequency at the terminal T6 when the voltage of the battery 2 falls below 4.3 volts to prevent the display of a distorted picture. The digital to analogue converter 122 produces line deflection rate controiling waveforms for controlling the integrators 27 and 28 (Figure 1) which generate the line scan waveforms and needed because of the geometry of the cathode ray tube 1. The purpose and operation of the digital to analogue converter 123 will be described later.The line logic circuit 121 also produces signals P1 and P2 identifying the odd and even fields on conductors 128 and 129 which are applied to a field separator circuit 130 which receives the field frequency pulses from the sync separator 113 via a conductor 131. The field sync pulses from the separator 130 are applied via a conductor 132 to a field logic circuit 133 which receives the digital output from a field counter 134 driven by pulses from the counter 119. Blanking signals from the field logic circuit 133 are fed to a switch 135 to ground the terminal T4 and thereby hold the cathode ray tube spot at the left-hand side of the frame during field flyback.The field logic circuit 133 also produces line number standard switch output which is conveyed via a conductor 136 to the oscillators 108 and 117 and to the line and field counters 119 and 134 to enable the receiver to handle different television standards. The digital outputs from the field counter 134 are also applied to a field digital to analogue converter 137 which produces field scan drive signals on terminals T7 and T8. The output of the correction digital to analogue converter 123 is applied as the reference voltage for the converter 137. This correction is needed because the cathode ray tube 1 is a flat tube in which the screen lies end on to the electron gun. It will be appreciated that with a tube of this type if the field deflection voltage is kept constant whilst the line deflection voltage is varied to generate a line, the resulting picture would be trapezoidal in shape.

In order to produce a rectangular picture, it is necesaryto adjust the field deflection voltage as a line is described by the spot and the purpose of the converter 123 is to cause the field deflection voltage output of the field digital to analogue converter 137 to be adjusted according to the position of the spot along the line so as to produce a rectangular picture.

The integrated circuit 9 also includes a 3.2 volt power supply 138 and a 3 volt power supply 139 energised from the main battery supply line 4 via terminal T12. The 3.2 volt supply is connected internally to the EHT INHIBIT circuit 127 and to the terminal T9. The 3 volt supply is connected just to the terminal T14. Earth connections are provided at terminals T5 and T10 and terminals T1, T3, T21 and T22 are provided for the connection of relatively large capacitances to the circuit.

It is not proposed to enter into a detailed description of the generation of the scanning signals and the operation of the circuits directly associated with this because these form the subject of other copending patent applications. The operation of the parts of the integrated circuit is otherwise fairly conventional for a television receiver, but where the circuit departs from the usual it will either be described later on in the present patent application or in another co-pending patent application.

From a consideration of the circuit as described above it will be clear that there are three regulated supplies, the 3.2 volt supply 138 and the 3 volt supply 139 in the integrated circuit 9 and the tuning voltage source derived by the potentiometer 8 from across a zener diode 140 which is connected to the 3 volt supply 139. These regulated voltages are used for those parts of the circuit which need them for stable operation, the tuner 7, and the integrated circuit 9, in particular the voltage controlled oscillators 108 and 117 and the digital to analogue converters 122, 123 and 137.

All of the voltages applied to the cathode ray tube 1 are derived from the battery 2 without regulation or stabilisation. The transistor 16 acts as a switch to interrupt the application of the battery voltage to the primary of transformer 17, from which is derived the heater supply for the tube 1 as well as the supply on conductor 141 for the video amplifer 13 connected to the control grid of the tube 1. The stabilised tuning supply is also taken from the output of the transistor 16 but is stabilised separately from its other outputs.

The battery voltage is also connected to the collector of the transistor 23 through part of the winding of the autotransformer 24. The pulsed energisation of the transformer 24 produced by turning off the transistor 23 with each line pulse results in higher pulsating voltages, one of which is rectified by a diode 142 and conveyed by the conductor 30 to power the frame deflection amplifier 22 and provide the voltage for a focus adjustment potentiometer 143. Another high pulsating voltage is produced on the conductor 31 and drives the diode-capacitor stack 32 which provides the supply voltages for the accelerator electrodes of the electron gun, the standing voltages for the deflection electrodes and repeller supply as well as the EHT for the cathode ray tube 1.The transformer 24 also supplies the drive pulses on conductors 25 and 26 for the integrators 27 and 28 which produce the line scan sawtooth waveforms.

From the above description of the generation of the voltages, both fixed and variable, which are applied to the cathode ray tube 1, it will be evident that the manner of their generation is such that they all bear a substantially constant relationship to the voltage produced by the battery 2. As a result of this the variation in the battery voltage with age has substantially no effect on the geometry of the display produced by the tube, since the reduction in the deflection voltages is matched by the reduction in the acceleration voltages, which means that the actual deflection of the beam is virtually unchanged.

In addition, the beam focussing will be retained.

Therefore the only effect of the falling battery voltage apparent to the viewer is a slight reduction in the brightness of the display.

Although the invention has been described with reference to a battery operated television receiver, and indeed it is of most value in such a receiver because of the power saving resulting from the omission of voltage regulation circuitry, it can also be used in other apparatus with an electrostatically deflected cathode ray display tube and/or powered from a voltage source other than a battery, for example, in a cathode ray tube display for a computer.

Claims (9)

1. Atelevision receiver having an electrostatically focussed and deflected cathode ray display tube in which all focussing and deflection voltages applied to the tube are derived from the same unregulated supply voltage source without stabilisation or regulation in such a way that the display is substantially unaffected geometrically by changes in the supply voltage.

2. A receiver according to claim 1 including an E.H.T. generating circuitforenergising electron beam focussing and accelerating electrodes of the tube, the circuit being supplied by the unregulated supply voltage, wherein the circuit also provides the datum voltages for the deflection electrodes.

3. A receiver according to claim 2 wherein the deflection voltages are applied to the deflection electrodes through capacitors from push-pull circuits powered by the unregulated supplies derived from the unregulated supply voltage.

4. A receiver according to claim 2 or 3 including first and second circuits energised by the unregulated supply voltage and driven by pulses at line frequency, wherein the first circuit includes the E.H.T. generating circuit and a line scan deflection circuit and also supplies the energisation for a field scan deflection output circuit, and the second circuit provides energisation for the cathode heater of the cathode ray tube and a video signal output stage.

5. A receiver according to claim 4 wherein the second circuit also feeds line flyback blanking pulses to the cathode of the cathode ray tube.

6. A receiver according to any preceding claim wherein the supply voltage source is a battery.

7. A circuit arrangement including a cathode ray tube, and line and frame scanning circuits wherein the line scanning circuit is connected to the heater circuit for the cathode ray tube so as to raise the potential of the heater during line flyback periods so as to cut off the electron beam during such periods.

8. An arrangement according to claim 7 wherein the energisation of the heater is effected via a transformer winding by pulses at line frequency, positive-going pulses derived from the line frequency pulses being applied to the transformer winding during line flyback periods.

9. A circuit arrangement for blanking the spot of a raster-scanned cathode ray tube during the line flyback periods substantially as described herein with reference to Figure 1 of the accompanying drawings.