GB1558492A

GB1558492A - Television receiver circuits

Info

Publication number: GB1558492A
Application number: GB3738176A
Authority: GB
Original assignee: Deutsche ITT Industries GmbH; ITT Industries Inc
Current assignee: TDK Micronas GmbH; ITT Inc
Priority date: 1975-09-13
Filing date: 1976-09-09
Publication date: 1980-01-03
Also published as: DE2540965A1

Description

(54) TELEVISION RECEIVER CIRCUITS (71) We, ITT INDUSTRIES INC., a Cnr- poration organised and existing under the Laws of the State of Delaware, United States of America, of 320 Park Avenue, New York 22, State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to television receiver circuits, and is an improvement in, or modification of, the invention disclosed in our Application No. 9382/75 (Serial No.

1.495,173).

Television receivers are already commercially available which, in addition to the main screen, are provided with a second screen of substantially smaller picture area, so that the viewer, in addition to his chosen programme being displayed on the main screen, can simultaneously watch a further programme on the smaller secondary screen.

Besides the investment involved in the second picture tube, such a receiver, as a rule, requires two complete sets of parts for receiving the different programmes, that is, the tuner, the IF-amplifier, video stages, and deflection circuits must be provided for twice. This involves a considerable additional investment.

Another method for simultaneously displaying two different television programmes has been demonstrated at exhibitions, as is described in the German technical journal "radio mentor electronic", March 1974, page 95. In this, one of the pictures to be displayed on the TV receiver screen is received and displayed in the usual way. By a second reseiver there is received a further station whose screen picture is again sampled by a television camera. The output signals of the television camera are then fed to the first receiver and displayed alternately by means of an electronic switch. with this arrangement capable of being made in such a way that the second picture is displayed in a section of the first picture. A similar method has also been disclosed in the German Published Patent Application (DOS) 2,239,593. These solutions, too, involve a considerable investment and are unsuitable for being used especially with domestic TV receivers.

In distinction thereto, our Application 9382/75 (Serial No. 1,495,173) proposes a television receiver which permits the simultaneous reception of at least two progammes, and is substantially more simple in its construction that the television receivers described above, comprising two separate picture tubes and receiving units. For the sake of enabling a better understanding of the present invention, there will first of all be described in greater detail the television receiver according to the aforesaid application, with reference to Figures 1 and 2 of the accompanying drawings, of which: Figure 1 schematically shows the front view of a television receiver according to the aforesaid application; and Figure 2 shows the block diagram of the television receiver according to the aforesaid application.

Figure 1 shows the result as obtainable by the viewer on the screen 2 of the television receiver 1, namely that the programme I is displayed on the major part of the screen 2, for example, a football match, while the picture section 2a displays another programme II. In the case of the 625-line television standard, the number of lines of the second picture 2a may amount to 45 lines, with the picture diagonals having a length of about 10 cm. Accordingly, the number of lines and the number of picture elements in the image section 2a are considerably reduced with respect to the reproduction of programme II when displayed as the main programme on screen 2. This is admissible because the image section 2a displays the total picture of programme II on a reduced scale.

The block diagram of an embodiment of the TV receiver according to the aforesaid application, shown in Figure 2, illustrates the signal path common to both programmes, extending from the antenna via the tuner 3, the IF-amplifier 4, and the video amplifier 5 to the picture tube 6, with the horizontal deflecting stage 7 and the vertical deflecting stage 8 still being associated with this signal path in the usual way. Moreover, the television receiver 1 still contains the audio amplifier 9 and the loudspeaker 10.

This shown common signal path is now acted upon by the storing and switching unit 11 as controlled by the output of the IF amplifier 4 and by the output of the horizontal deflecting stage 7 and which, in turn, acts upon the tuner 3, the IF amplifier 4 and the video amplifier as follows.

Assume that the tuning means of the tuner 3, for example, varactor diodes with the corresponding potentiometers for the voltage adjustment thereof, have been set to the station for receiving programme I and to the station for receiving the other programme II. In dependence upon the horizontal stage 7, the storing and switching unit 11 now controls the tuner 3 in such a way that during certain lines it is switched from programme I to programme II. During these lines the video amplifier, by the action of the switching device of fhe storing and switching unit 11, is connected to the storage portion thereof, so that the lines of the now received and processed programme TI are stored in the storage portion.

Besides the switching of the tuner 3 to programme 11 there is also caused a corresponding switching of the gain of the IF amplifier 4.

The storage portion transfers the information as stored therein, to the video stage as soon as the electron beam sweeping the screen, reaches the area of the image section 2a.

The storage portion is aimed at reducing in size the picture of programme II, and at bridging the time difference between the switching to the station of programme II and the reproduction (display) of this information. Reduction in size of the picture of programme 11 is accomplished in that the readout speed of the storage device is higher than the speed at which the information was written in.

It is of advantage to effect the switching of the tuner 3 to programme II only a line at a time, in order thus to disturb the reception of the programme I as little as possible.

Because the information flow of programme I to the picture tube 6 is interrupted during the time required for the switching to programme II, it is necessary, during this time, to coffer a "substitute programme" to the picture tube 6. The signal intended for this purpose, in the most simple case, may consist of the medium brightness value, hence of the medium grey value, of the preceding lines. With respect to colour television receivers it is advisable at least to continue with the representation of the colour information, with the colour information to be further represented, in the case of a colour television receiver operating on the PAL-system principle, corresponding to the colour signal of the preceding line, or in other words, the colour information which is to be continued to be represented, is simply taken from the delay line as contained in the receiver.

Programme I is least disturbed if, in the case of a colour television receiver; and in addition to the aforementioned colour information, also the brightness information of the preceding line is fed to the picture tube while programme II is being stored into the storage device.

As regards the last-mentioned case it will be necessary to provide an additional storage portion for storing the brightness information of the preceding line until the switching to programme II is being carried out. This additional storage portion may be of a relatively simple design if the bandwidth of the signal of the switched line is reduced considerably, for example, by the factor 10. This may be carried out without further ado, because the picture element resolution of this line does not need to be very high considering that the line which is being represented again, is actually a "wrong" one.

As already mentioned, it will result from the representation of programme II as a total picture on a reduced scale, which is written at a normal raster resolution, that the number of lines as well as the number of picture elements per line to be stored with respect to this information, can be reduced by the imaging scale. An adequate picture of the programme contents is obtained when providing for about 50 lines with about 50 picture elements.

The storage portion for programme II as contained in the storing and switching unit 11, is preferably designed in the way to be described hereinafter. It consists of storage positions for the lines of programme II linewisely arranged, with the number of storage positions corresponding to the number of lines to be stored. The first line of programme II is put into the first storage positions. After the tuner has been switched back to programme I, the stored first line of programme II is shifted into the next storage position, so that now the first storage position is set free for the second line of programme II to be stored. This shifting of the individual stored lines of programme II in the individual storage position is continued until the first stored line has reached the last storage position. Thereafter, the storage position will contain a picture of programme IT. This linewise shifting is preferably carried out by way of parallel transfer, but may just as well be carried out by way of serial transfer. The storage portion thus forms a first-in-first-out store (fifo sore) in that its contents can be read out in the same order in which they were written in.

Now the stored picture may be displayed on the screen of the picture tube by means of a corresponding sequence control. During the time in which the picture of programme II is displayed on the screen of the picture tube, the storage contents may rotate continuously.

As a simplification, it is possible to display the same storage contents in both fields, thereby avoiding the higher resolution of an interlaced picture. This is possible because the resolution in the vertical direction still remains of the same order as the horizontal resolution. By this measure it is possible to halve the number of required storage positions.

From the consideration that the speed of movement of an object, such as a football, shown in programme II, does not need to be higher in the picture section of programme II than in programme I, it follows that the number of new pictures of programme II to be stored, may be reduced in proportion to the scale of reduction. This gives the advantage that the disturbance of programme I caused by the switching of the tuner necessary for the storing-in, will be considerably reduced.

Moreover, the circuit of the storing and switching unit 11, is designed in such a way that only n/m lines of programme II will be taken out during each picture passage of programme L with n being the number of lines of the picture of programme II on an enlarged scale, and m being the number of storage passages chosen for renewing the entire storage contents (the number m, for example may be = 1).

Both programmes (I and II) can be selected from the programmes offered by the available stations, so that as a rule, both programmes are controlled by different master clocks. On account of this, however, the individual lines of programme II to be stored, will be stored in arbitrary storage positions of the storage portion i.e. the be ginniflg of the line and the end of the line are no longer in agreement with the beginning and the end of the corresponding storage position. This, however, is to be avoided with a view to achieving a display that will make sense, and this can be achieved in that the information contained in the corresponding storage position is permitted to rotate until the line synchronizing pulse appears at a certain point, e.g. at the end of the storage position. Since the vertical synchronizing pulse of the picture reduced in size is also not in phase with that of the picture of programme I, a corresponding assignment is also necessary in this case.

A simple picture pulse search circuit which may consist of a conventional pulse separating circuit with an integrating network, controls the storing of each line to be stored, into the corresponding storage position as soon as the vertical (picture) synchronizing pulse has been detected in a predetermined storage position.

In the storage portion of unit 11 a storage device such as the known types of charge transfer circuits, hence for example, bucket brigade circuits, charge-coupled devices, or the like can be used with advantage. Particularly suitable is the storage device described in our Application No. 26104/75 (Serial No. 1,470,637).

It is readily possible to display the picture of programme II also as a still which is taken at certain time intervals from the running programme, thus permitting the storage control to be further simplified. Of course, in that case there will have to be done without the information relating to movement, as contained in programme II which, depending on the opinion on quality and the attention being paid to programme II by the viewer, may be considered to be of secondary importance only.

According to the present invention there is provided a television receiver in which on one screen a first programme can be displayed and at least one second programme can also be displayed simultaneously and on a reduced scale and receivable on a different frequency inset within the image of the first programme, comprising a storage portion in which the picture contents of the second programme are stored with a reduced number of lines and, thereafter, read out in a linewise fashion in an appropriate position of the lines of the first programme, the receiver having one common signal path (tuner, IF-amplifier, video amplifier), and a switching means for switching the tuner at the occurrence of those lines of the picture of the second programme which are to be stored, from the receiving frequency of the first programme to that of the second programme, and comprising a circuit which, during the time required for storing one line of the second programme into the storage portion of said equipment, blanks out the corresponding line of the selected first programme writes the subsequently following lines of the first programme which again contain video-information, where the blanked line should have been written, and compensates for the reduced vertical extension of the picture caused by the omission of lines by stretching the height of the vertical deflection.

Embodiments of the invention are described below with reference to the Figures 3 to 6 of the accompanying drawings, of which: Figure 3 shows an integrator as used with a first embodiment; Figure 4 shows various current waveforms relating to the embodiment according to Figure 3; Figure 5 shows the circuit of a second embodiment; and Figure 6 shows diagrams of various pulses appearing in the embodiment according to Figure 5.

Figures 3 and 4 refer to a first embodiment superimposing an additional current onto the linearly increasing vertical deflecting current so that the rise of the vertical deflecting current is interrupted during the time required for storing one line of programme II into the storage portion of the unit 11 of Figure 2 with the latter being kept constant at the just assumed value, with the constant rise, hence the increase of the vertical deflecting current and the final value thereof, being enlarged to such an extent that the total amplitude will become equal to that of the vertical deflecting current which is not being acted upon.

Figure 3 shows a circuit suitable for generating the aforementioned additional current. This circuit, substantially, consists of an integrator for generating from the squarewave pulses having a time duration t" and serving to switch the tuner 3 to programme IL and which are fed in at the input A, a signal having sloping sections, which have the same slope but opposite sign as the vertical deflecting current and which between these sections, keeps a constant amplitude which is lower between each succeeding pair of sections.

Thereafter, the output signal of the integrator is fed to the voltage-current converter 12 which, for example, may consist of a voltage-controlled constant current source of conventional type, with the output current Ix thereof being superimposed upon an enlarged vertical deflecting current IH as generated in the vertical deflection stage 8, in the proper sign relationship.

In particular, the integrator according to Figure 3, consists of a first transistor T1 operated in a grounded-emitter connection with a collector resistance R2, whose base is connected to the input A. The collector of transistor T1 through a capacitor C1 and a resistor R1, is connected to the emitter of a second transistor T2 operated in a grounded base connection, with the collector thereof, via the parallel arrangement of a capacitor C2, being applied to the main current path of a thyristor Ty at the voltageconducting pole of the source of supply voltage U3.

Through diode D1 the point connecting the capacitor Cl and the resistor R1 is connected to the zero point of the circuit, so that the cathode of the diode, in the case of a positive pole of the source of supply voltage UB, is connected to the zero point of the circuit. In this case, as may be taken from Figure 3, the transistors T1, T2 are npn-type transistors.

The gate electrode of the thyristor Ty is connected to the input B to which the picture synchronizing pulses are fed, so that the capacitor C2 is discharged again during the repetition of pictures.

The capacitor C1 is charged across the resistor R2 and via the diode D1 during the intervals between the squarewave pulses.

During each squarewave pulse applied to the input A and having a pulse width tu at least corresponding to the duration of one line.

hence to at least 64 Fs in the case of the 625-line television standard, the capacitor C1 is discharged via the then conducting base-emitter diode of transistor T2, this having the effect of causing a lowering of the collector voltage of T2.

In Figure 4 wave form (a) is the enlarged waveform of the sawtooth-shaped vertical deflecting current IH which exceeds in final amplitude the amplitude N of a non-enlarged deflecting current (awl) by the amount E.

Waveform (b) is the output current 1K of the voltage-current converter 12 which in shape corresponds to that of the collector voltage of the transistor T2 shown in Figure 3. Waveform (c) is the sum of these two currents when superimposed. During the times tu, hence during the squarewave pulses effecting the switching of the tuner 3, there is no variation of the vertical deflection, so that the line containing no video informa tion, will be overwritten by the next succes sively flowing line again containing video information. The final amplitude of the sum IH + IK corresponds to the final ampli tude N of a non-enlarged vertical deflecting current.

Figures 5 and 6 refer to a second type of embodiment of the invention in which, unlike the just-described embodiment, not the vertical deflecting current of the picture tube, but the vertical oscillator is being acted upon. This embodiment relates to vertical oscillators of the resistance capa citance type in which a capacitor is charged by a constant current through at least one resistor. The charging of the capacitor is stopped during each time used for storing one line of programme II into the storage portion of unit 11, and the charging current is enlarged with respect to the non-influenced case in such a way that the total amplitude of the vertical oscillator voltage becomes equal to that of the non-influenced total amplitude.

Figure 5 shows a suitable circuit arrangement. The vertical oscillator consists of a capacitor C one pole of which is connected to the zero point of the circuit, and of a resistor R arranged in series therewith.

Resistor R is, in fact, a combination of all those resistors which, in a vertical oscillator of the customary type are arranged between the capacitor C and the live pole of the source of charging voltage, hence for example, further fixed and/or adjustable resistors serving to fix the rise and the total amplitude of the vertical oscillator voltage. By way of a transistor T3, operated in a grounded-emitter connection, and a diode D2, the capacitor C is always discharged when the base connected to an input F, is being acted upon by the picture synchronizing pulse.

A series resistor Rs and the collectoremitter path of a first switching transistor T4 are provided in the charging circuit of the capacitor C. The series resistor Rs is connected on one hand to the resistor R and, on the other hand, to the collector of the switching transistor T4 whose emitter is applied to the live pole of the source of supply voltage UB. The base of the switching transistor T4 is controlled in dependence upon the squarewave pulses switching the tuner 3 of Figure 2.

This is effected with the air of transistor T6 whose base is retained at a constant voltage with the aid of a zener diode Z and a resistor R3, because the series arrangement of both the resistor R3 and the zener diode Z is being fed with the supply voltage UB. The emitter of transistor T6 which, on one hand, is connected to the zero point of the circuit through a resistor R4, on the other hand is connected through a diode D3, to an input E to which squarewave pulses are applied which effect the switching of the tuner 3. In this arrangement, the cathode of the diode D3 is connected to the emitter. The collector of transistor T6, through a resistor R5, controls the base of transistor T4.

Accordingly, when a squarewave pulse having the width tu and serving to effect the switching of the tuner 3, appears at the input E, the transistor T4 is blocked for this period of time, thus interrupting the charging of the capacitor C as is schematicallv shown in Figure 6 waveform c. Accordingly, the capacitor voltage Uc will each - time remain constant for the period of time tu.

The emitter-collector path of a second switching transistor T5 is arranged in parallel with the series resistor Rs, this switching transistor T5, by means of its base electrode, being switching to the conducting state during the time required for storing the lines of programme II into the storage portion of unit 11. For this purpose there is used a transistor T7 which is operated in a grounded-emitter connection, with the base thereof being applied through a resistor R9 to the input E, and through a resistor R6 to the zero point of the circuit. The collector of transistor T7 is connected through a resistor R7, to the base of the switching transistor T5 which, through a resistor R8, is connected to its own emitter.

The collector of transistor T7 is coupled to the zero point of the circuit through a capacitor C3. By properly dimensioning the latter, it is ensured that the collector voltage of transistor T7 will rise so slowly during the intervals between the squarewave pulses effecting the switching of the tuner 3, that the conducting transistor T5 is prevented from being switched to the nonconducting state prior to the arrival of a further squarewave pulse. Therefore, if the tuner switching is terminated, and if accordingly, no further squarewave pulses appear, the collector voltage of transistor T7 may rise until the transistor T5 is switched to the non-conducting state, thus eliminating the short circuit of the series resistor Rs, so that the amplitude of the vertical oscillator voltage which had been increased on account of this short circuit, will return to the value of the non-influenced case.

When the polarity of the live pole of the source of supply voltage UB is chosen positive as here, the two switching transistors T4 and T5 are of the pnp-conductivity type, while the remaining transistors T3. T6 and T7 are of the npn-conductivity type.

Figure 6 shows some waveform diagrams of pulses appearing in the circuit shown in Figure 5. The representation has been chosen thus that the time axis t is shown to be interrupted several times in order to be able to represent important waveforms.

Waveform (a) shows the squarewave pulses applied to the input E and effecting the switching of the tuner 3. As mentioned above, the period ta of these pulses at least corresponds to the duration of one line.

Every fifth line contains no video information.

Waveform (b) shows the picture synchronizing pulse which is shown to be applied to the input F.

Waveform (c) shows the capacitor voltage Uc.

The first four vertical oscillator periods have horizontal waveforms which are caused by the squarewave pulses of waveform (a), whereas the fifth sawtooth pulse in waveform (b) shows to have the usual non influenced shape of a vertical deflecting pulse, because no signal is applied to the input E.

WHAT WE CLAIM IS:- 1. A television receiver in which on one screen a first programme can be displayed and at least one second programme receivable on a different frequency can also be displayed simultaneously on a reduced scale and inset within the images of the first programme, comprising a storage portion in which the picture contents of the second programme are stored with a reduced number of lines and, thereafter, read out in a linewise fashion in an appropriate position of the lines of the first programme, the receiver having one common signal path (tuner, IF-amplifier, video amplifier), and a switching means for switching the tuner at the occurrence of those lines of the picture of the second programme which are to be stored, from the receiving frequency of the first programme to that of the second programme, and comprising a circuit which, during the time required for storing one line of the second programme into the storage portion of said equipment, blanks out the corresponding line of the first programme.

writes the subsequently following lines of the first programme which again contain video information, where the blanked line should have been written, and compensates for the reduced vertical extension lf the picture caused by the omission of lines by stretching the height of the vertical deflection.

2. A receiver as claimed in claim 1, in which both the final value and the rise of the vertical deflecting current of the picture tube are increased with respect to the noninfluenced case, the rise of the vertical deflecting current is periodically interrupted, the current being kept constant at the just assumed value, by an integrator which generates from squarewave pulses switching the tuner to the second programme, a signal with sections having the same slope, but different sign, as the enlarged vertical deflecting current, intermediately arranged sections of constant amplitude which is increased from section to section, and a current corresponding to this signal, which is superimposed upon the vertical deflecting current in the proper sign relationship, both the final value and the rise of the vertical deflecting current being so increased that subsequently to the superimposition, the final value of the vertical deflecting current is equal ta the final value of the non-influenced vertical deflecting current.

3. A receiver as claimed in claim 2, in which said integrator consists of a first transistor operated in a grounded-emitter connection, to the base of which there are applied the squarewave pulses effecting the switching of the tuner to the second programme, and whose collector, via a first capacitor and across a resistor is connected to the emitter of a second transistor operated in a grounded-base connection; in which between the point connecting the first capacitor to the resistor, and the zero point of the circuit, there is arranged a diode in such a way that the cathode thereof, in the case of a positive live pole of the source of supply voltage, is applied to the zero point of the circuit: and in which the collector of the second transistor, via a second capacitor arranged in parallel with the main current path of a thyristor, is connected to the live pole of the source of supply voltage, the gate electrode of the thyristor being supplied with a picture synchronizing pulse.

4. A receiver as claimed in claim 1, in which, where the receiver employs an RC- vertical oscillator whose capacitor is

Claims

**WARNING** start of CLMS field may overlap end of DESC **. influenced shape of a vertical deflecting pulse, because no signal is applied to the input E. WHAT WE CLAIM IS:-

1. A television receiver in which on one screen a first programme can be displayed and at least one second programme receivable on a different frequency can also be displayed simultaneously on a reduced scale and inset within the images of the first programme, comprising a storage portion in which the picture contents of the second programme are stored with a reduced number of lines and, thereafter, read out in a linewise fashion in an appropriate position of the lines of the first programme, the receiver having one common signal path (tuner, IF-amplifier, video amplifier), and a switching means for switching the tuner at the occurrence of those lines of the picture of the second programme which are to be stored, from the receiving frequency of the first programme to that of the second programme, and comprising a circuit which, during the time required for storing one line of the second programme into the storage portion of said equipment, blanks out the corresponding line of the first programme.

4. A receiver as claimed in claim 1, in which, where the receiver employs an RC- vertical oscillator whose capacitor is charged to a constant current value across at least one resistor, the charging of the capacitor is respectively interrupted during the time required for storing one line of the second programme into the storage portion; and in which the charging current is increased in such a way with respect to the on-influenced case, that the total amplitude of the vertical oscillator voltage becomes equal to that of the non-influenced total amplitude.

5. A receiver as claimed in claim 4, in which into the charging circuit of the capacitor there are inserted a series resistor and the collector-emitter path of a first switching transistor whose base is controlled in dependence upon squarewave pulses which cause the switching of the tuner; and in which to the series resistor there is connected in parallel the collector-emitter path of a second switching transistor, to the base electrode of which there is applied a signal by which it is switched to the conducting state during the time required for storing the lines of the second programme into the storage portion.

6. A television receiver substantially as described with reference to Figures 3 and 4, or Figures 5 and 6 of the accompanying drawings.