DE2812549A1 - TELEVISION RECEIVER WITH A DEVICE FOR THE SIMULTANEOUS PLAYBACK OF MULTIPLE PROGRAMS - Google Patents

Description

E. Zaehringer - 2 Fl 959

Television receiver with a device for the simultaneous playback of several programs

Addition to patent 24 13 839 and patent 25 42 502 (patent applications P 24 13 839.4-31 and P 25 42 502.9).

There are television receivers already commercially available, where additionally to the main screen there is a second screen, which is much smaller in its area, so that the viewer can use it in addition to the program of interest running on the main screen, another program on the small one Secondary screen can be followed.

In addition to the expense for the second picture tube, such a receiver generally requires two complete receiving parts for the different programs, d. i.e., tuner, IF amplifier, There must be duplicate video stages and deflection circuits. This means a considerable additional effort.

At exhibitions, a different method of making two different ones visible at the same time has occasionally been used Demonstrated television programs, see the magazine "radio mentor electronic", March 1974, p one of the images to be displayed received and displayed by a television receiver in the usual way. With a second The receiver receives another transmitter whose shielding

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image is in turn scanned by a television camera. The output signals from the television camera are then sent to the first receiver fed and shown alternately by means of an electronic switch, the arrangement being chosen it can be seen that the second image can be seen in an image section of the first. A similar procedure is also used in the DE-OS 22 39 593 described. These solutions also involve considerable effort and are particularly useful for home recipients not feasible.

In contrast, the first main patent 24 13 839 gives a television receiver for the simultaneous reception of at least two programs, which is much simpler in its structure than the known television receiver described above with two separate picture tubes and receiving units. For better understanding the present invention will therefore first be based on the television receiver of the first main patent in detail 1 and 2 of the drawing explained in more detail.

Fig. 1 shows schematically the front view of a television receiver according to the first main patent, and

Fig. 2 shows the block diagram of the television receiver according to the first main patent.

In Fig. 1, the desired result on the screen 2 of the television receiver for the viewer is shown, namely that the program I, for example a soccer game, is visible on the majority of the screen 2, while in one Section 2a of the further program II is made visible. With the usual 625-line standard, the number of lines in the Image section 2a, for example, be 4 5 and the length of the image diagonal is about 10 cm. The number of lines and the pixel

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The number of the image section 2a is therefore compared to the reproduction of the further program II as the main program on the screen 2 greatly reduced. This is easily permissible, since in the image section 2a generally a reduced overall image of the further program II is shown.

The block diagram shown in Fig. 2 shows an embodiment of the television receiver according to the first main patent the common for both programs signal path from the antenna via the tuner 3, the intermediate frequency (IF) amplifier 4 and the video amplifier 5 to the picture tube 6, this signal path in the usual way still the horizontal deflection stage 7 and the Vertical deflection 8 are assigned. The television receiver also contains the audio amplifier 9 and the loudspeaker 10.

The memory and switching stage 11 now acts on the described common signal path, with it on the one hand from Output of the intermediate frequency amplifier 4 and the horizontal deflection stage 7 is controlled and in turn to the tuner 3, the intermediate frequency amplifier 4 and the video amplifier acts in a manner to be described.

It is assumed that the tuning means of the tuner 3, for example Capacitance diodes with corresponding potentiometers for their voltage setting on the transmitter for program I. and the station for further program II are set. The memory and switching stage 11 now controls as a function of the horizontal stage 7 the tuner 3 in such a way that during certain lines of the program I to the further program II is switched. During these lines, the video amplifier is connected to the memory and switching stage 11 by the switching part whose memories! 1 are connected, whereby the lines of the now received and processed further program II in the

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Memory can be written. In addition to switching tuner 3 to further program II, a corresponding Switching the throughput gain of the intermediate frequency amplifier ^ 4 causes.

The memory then returns the information written into it to the video stage when the one overwriting the screen Electron beam arrives in the area of the image section 2a.

The memory has the task of reducing the image of the further program II and the time difference between the switchover to bridge to the transmitter of the further program II and the reproduction of this information. The reduction of the image of the further program II is achieved in that the output speed for the memory is greater than the input speed is.

It is advantageous to switch the tuner 3 to the further program II only line by line in order to receive the Program I to disturb as little as possible.

Since the flow of information from the program I to the picture tube 6 is interrupted during the switchover to the further program II is, it is necessary to offer the picture tube 6 a "replacement program" during this time. The signal intended for this can in the simplest case consist of the mean brightness value, i.e. the mean gray value, of the preceding lines. in the Color television is a good choice, at least the color information to be shown further, in the case of a color television set according to the PAL system, the color information to be further displayed corresponds to the color signal of the previous line, d. This means that the color information to be displayed is simply taken from the existing delay line in the device.

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Program I is least disturbed when on the color television set of the picture tube during the writing of the further program II in the memory in addition to the mentioned color information also the brightness information of the previous one Line is fed.

For the latter case, an additional memory is required, in which the brightness information of the previous Line is saved until switching to the other program II. This additional memory can be constructed in a relatively simple manner if the bandwidth of the signal of the switching line is significant, for example by a factor of 10. This can easily be done because the pixel resolution of this Line does not need to be very high, because the line shown again is actually a "wrong" Line is.

As already mentioned, the representation of the further program II as a reduced overall picture results from that with normal Raster resolution is written that the number of lines to be stored for this information and the number of pixels per Line can be reduced by the reproduction scale. A good recognition of the program content is already at approx. 50 Lines with about 50 pixels are obtained.

The memory contained in the memory and switching stage 11 for the further program II is advantageously structured as described below. It consists of arranged in lines Storage locations for the lines of the further program II, the number of storage lines being the number of corresponds to the lines to be saved. First, the first line of the further program II is in the first memory line enrolled. While the tuner is back on program I.

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is switched, the first line of the stored further program II is shifted to the next memory line, so that the first memory line for the second line of the further program II to be stored has become free again. This shifting of the individual memory lines is carried out until the first stored line is in the last Memory line has arrived. Then there is a complete one Image of the further program II in the memory. The line-by-line shift is advantageously carried out by means of parallel transmission made, but can also be done by serial transmission.

The saved image can now be controlled by a corresponding sequence control can be displayed on the picture tube. During the display time of the picture of the further program II on the The contents of the memory in the picture tube can continuously circulate.

As a simplification, the same memory content can be used in both partial images are shown, with a deliberate decision not to use a higher resolution due to the interlaced image. This is possible, since the resolution in the vertical direction still remains in the order of magnitude of the horizontal resolution. By this measure the number of storage spaces required can be halved.

Considering that the speed of movement of an object shown in program I, e.g. B. a football, im Image section of the further program II not to be larger needs than in program I, it follows that the number of new images to be stored in further program II is proportional to the Reduction scale can be reduced. This has the advantage that the required for storing Switching the tuner-related disturbance of the program I is greatly reduced.

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The switching part of the memory and switching stage 11 is also like this designed so that only n / m lines of the further program II are removed during each image cycle of the program I, where η is the number of lines of the reduced image of the further program II and m is the number of memory passes that is selected for the renewal of the entire memory content (the number m can also be = 1, for example).

Both programs (I and II) should be able to be chosen from the available channels and programs, so that in the generally both programs can be controlled by different clocks. As a result, however, the individual items to be saved can be saved Lines of the further program II in any memory locations in the memory, d. i.e., the beginning of the line and the end of the line no longer match the beginning and end of the corresponding memory cell. For a meaningful rendering, this is therefore to avoid, which can be achieved by using the information contained in the corresponding memory line can circulate until the line sync pulse on one specific place, e.g. B. at the end of the memory line appears. Since the image sync pulse of the reduced image with the of the picture from program I is not in phase, an assignment is also required here. A simple picture pulse search circuit, which can consist of a conventional pulse separator circuit with an integration element, controls the storage of everyone storing line in the memory lines provided as soon as the image sync pulse is detected in a specific memory line has been.

The memory can advantageously be used in the manner of the known charge shifting circuits, So, for example, bucket chain circuits, charge-coupled components or the like. Particularly advantageous is the one in the DE-OS 24 30 349 described memory.

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It is easily possible to show the shown picture of the further program II as a still picture, the current one Program is taken out at certain time intervals, whereby the memory control can be simplified. However, waived then on the movement information contained in the further program II, which, however, depends on the evaluation and the dem attention paid by the viewer to further program II is of minor importance.

According to one embodiment of the first main patent is used for the simultaneous playback of both programs a common signal path (tuner, IF amplifier, video amplifier), and a Switching part switches the tuning means of the tuner during the lines of the picture of the further program to be stored by the Reception frequency of the first program to that of the further program around.

As the investigations on which the second main patent is based have shown, switching the tuner and the IF amplifier to the further program II interference in the audio channel, d. i.e. the useful signal emitted by the device loudspeaker an interference signal is superimposed which contains at least the frequency of the tuner switchover signal.

The second main patent specifies suitable circuits for suppressing this interference signal. To understand the invention first again the principle of one of these circuits explained in more detail with reference to FIGS. 3 and 4. FIG.

Fig. 3 shows the basic circuit diagram of this circuit, and

FIG. 4 shows the profile of the input voltage and the output voltage in the arrangement according to FIG. 3.

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The circuit according to FIG. 3 is based on the knowledge that the narrow-band, mostly present in conventional television sets Ton IF filter implemented in the form of a ceramic filter for Filtering out the audio intermediate frequency signal, the frequency of which is known to be 5.5 MHz for the CCIR television standard and 5.5 MHz for the in the US standard is 4.5 MHz, to the tuner switching that takes place during one line of the others End reacts with a transient process that z. B. lasts about another line length, but can also be shorter. The audio signal is therefore for a time which is approximately the sum of the duration of the square-wave pulses switching over the tuner 3 and from the settling time of the tone IF filter is the same, disturbed and superimposed by the overshoot signal of the tone IF filter. This time is referred to as the total disturbance duration T in the following.

In FIG. 4, large letters are used to mark the individual in connection with the first square pulse shown in FIG t occurring curves. The one at the beginning of this disorder The signal value appearing in the audio signal is denoted by F and the signal value appearing at the end of this disturbance is denoted by G. In the circuit according to FIG. 3, the last one before the start of the switchover of the tuner 3 to the further program II the currently occurring signal value F of the audio signal NF for the total disturbance duration T by means of a sample-and-hold circuit stored and fed to the audio output amplifier instead of the audio signal for this time.

The audio signal NF passes through a special operational amplifier, which is operated as a sample-and-hold circuit for the total duration of the disturbance T by means of appropriate wiring. For this the operational amplifier 12 has the input c, via which the output resistance can be electronically controlled, and its

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Voltage gain is one by means of resistor R31 set. The negative feedback resistor R31 couples the output signal of the operational amplifier 12 to the inverting one Input e back, the output signal not directly at the output a of the operational amplifier 12, but at the load resistor R32 of the impedance converter connected downstream of the output a, which in the exemplary embodiment according to FIG the field effect transistor T31 operated in a source follower circuit with the drain resistor R33.

The capacitor C31 is located between the output a of the operational amplifier 12 and the circuit zero point. The input c, which influences the output resistance of the operational amplifier 12, is switched from the lowest possible value when operated as an operational amplifier to the highest possible value when operated as a sample-and-hold circuit via the transistor T operated in the emitter circuit as a switch with collector resistance R 34. Via the inputs b, d, the operational amplifier 12 is connected to the poles of the operating voltage _{source U R} , the negative pole of which is connected to the circuit zero point.

The duration of the switchover mentioned is equal to the total duration of the fault T. To generate pulses of this duration is shown in Fig. 3, the pulse shaping circuit 13, for example as monostable multivibrator can be realized, provided, the input E 'of which the tuner 3 switching square-wave pulses are fed and at the output, which is connected to the base of the transistor T, the pulses with the total duration of the disturbance T occur.

The audio signal NF is fed to the non-inverting input e of the operational amplifier 12 via the input E of the sample-and-hold circuit, while the "compensated" audio signal NF ¹

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via the output A at the source resistor R3 2 of the field effect transistor T31 is removed.

The curves shown in FIG. 4 illustrate the course of the input voltage u "and the output voltage u, the arrangement

L · ti

3. For the sake of simplicity, it is assumed that the audio signal is sinusoidal, the course of which during the total disturbance duration Tu. is superimposed by the aforementioned settling signal of the tone IF filter. This waveform is shown in Fig. 4a. The total interference duration T is made up of the duration t of the square-wave pulses switching the tuner and the settling time t _{f of} the audio IF filter: T = t _u + t _f .

_{The output voltage U 7} shown in FIG. 4b. does not contain the disturbance .impuls contained in Fig. 4a, but the signal value F of the audio signal NF occurring at the beginning of the disturbance is kept constant for the total disturbance duration T. The curve of the output signal U therefore "jumps" at the end of the disturbance to the then im Audio signal occurring signal value G.

For simple audio reproduction that does not place particularly high demands on the sound quality, that is explained with reference to FIGS. 3 and 4 Arrangement sufficient. Compared to this, a higher sound quality can be achieved with additional ones specified in the second main patent Achieve arrangements which, however, are not the starting point of the invention. Rather, this links to the solution of the same Task, namely circuits suitable for suppressing interference in the audio signal caused by the tuner switching indicate to the principle of the described arrangement according to FIG. 3 and develops it in the manner as shown in Claims 1 to 3 is specified.

The invention will now be explained in more detail with reference to the further figures of the drawing.

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Fig. 5 shows the block diagram of an embodiment of the invention,

Fig. 6 shows various curve shapes that occur in the arrangement according to Fig. 5,

Fig. 7 is a block diagram showing an embodiment of a development of the invention,

FIG. 8 shows various curve shapes occurring in the arrangement according to FIG. 7, and

FIG. 9 shows curves for the general explanation of FIG. 7.

In the exemplary embodiment according to FIG. 5, the audio signal NF is fed to the sample-and-hold circuit 14 via the input E. you The scanning signal H is made up of the square-wave pulses switching the tuner 3, which in turn consists of a signal from the horizontal deflection stage are derived as follows. The square-wave pulses are fed to the frequency multiplier 17, their Frequency f increased by the integer factor k. In addition to the integer condition, the following also applies to the factor k additional condition:

k £

^f u

The hold time t "of the sample-and-hold circuit 14 is thus obtained to

Ή kf
u

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The output of the frequency multiplier 17 is then the pulse shaper circuit 16, for example a monostable multivibrator, fed from it at a fixed frequency one suitable as the sampling signal H of the sample-and-hold circuit 14 Make pulse train as shown in Fig. 6c. During the short negative-going impulses, the amplitude of which is s in This embodiment is identical to the potential of the circuit zero point, is scanned, and during the Pulse times with the positive amplitude value h, the sampled value is stored, i.e. held.

The output signal NF of the sample and hold circuit 14 is in 6b, in which the audio signal NF disturbed by the tuner switchover is also shown as in FIG. 6a. In FIG. 6a also shows numerical values which correspond to such a tuner switch that during every fourth line of a field is switched to the further program II. This means that every 256 .us there is no sound signal for more than 64 .us to disposal. The sound interferences consist of integer multiples of the switching frequency f = 1/256, us = 3.9 kHz and their mixed products with the audio signal. The above-mentioned condition for k results in a value k = 3, so that t "= 85.3 ..., us is. This value is just slightly longer than the total disturbance duration T if the mentioned transient process of the tone IF filter is made much smaller than a line duration becomes what is practically possible.

The output of the NF sample-hold circuit 14 is in the embodiment of Fig. 5 conducted even through low pass filter whose upper cut-off frequency f equal to half the frequency of the sampling signal _TI H is to be selected. At output A.

ti

and thus the band-limited audio signal NF ¹ occurs at the input of the audio output amplifier.

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In the case mentioned with f = 3.9 kHz, the upper limit frequency of the low-pass filter 15 is thus 5.86 kHz. As both Speech and music transmissions, the signal components in the frequency range above 5 kHz compared to the associated fundamental vibrations are at least 40 dB smaller and these are further attenuated by the sample-and-hold circuit, can on an input-side band limitation which is necessary per se to avoid intermodulation, but which is difficult to implement be waived. Otherwise, the band limitation to 5.86 kHz only leads to a slight reduction in the quality of the TV sounds.

If, however, this reduction in quality is not acceptable, then, according to the development of FIG. 7, that according to the sampling theorem The band limitation at 5.86 kHz, which appears to be imperative, must be brought to a limit at twice the value of 11.7 kHz, d. H., With the circuit arrangement according to FIG. 7, the limitation given by the sampling theorem can be reduced by a factor of 2 to enhance. This is done in parallel with the signal path via the sample-and-hold circuit 14 and the low-pass filter 15 according to FIG. 5, a further signal path is provided which the second sample-and-hold circuit 18, the delay element 21, the electronic switch 23 and the additional low-pass filter 24 contains.

The characteristic of this parallel signal path is that the frequency f n of the sampling signal H2 of the second sample-and-hold circuit 18 is twice as great as the frequency f _T. = kf of the sampling signal H of the sample-and-hold switch

H U

device 14; so it is the relationship that counts

^f H2 = ^2kf u *

As a result, instead of the frequency multiplier 17 according to FIG. the double frequency multiplier 17 'provided at his

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both outputs generates the two frequencies kf and 2kf.

In the embodiment according to FIG. 7, the third sample-and-hold circuit 19 is also provided, with which the output signal of the low-pass filter 15, which here has one in the pass band constant transit time is sampled. The frequency of its sampling signal H3 is also equal to 2kf; it is however, it is delayed in time with respect to the sampling signal H2, which is achieved by means of the first delay element 20.

The output of the second sample and hold circuit 18 becomes. also delayed by means of the second delay element 21, the output of which is at the normally closed contact input 231 of the electronic switch 23. At its working contact 232 is the Output of the third sample-and-hold circuit 19, while the input of the additional low-pass filter 24 is connected to its output 234 is. Finally, the tuner switchover square-wave pulses delayed by means of the third delay element 22 are present at the control input 23 3. The delay time t of the three delay elements 20, 21, 22 is in each case equal to the sum of the signal delay times in the first sample and hold circuit 14 and the low-pass filter 15.

In the parallel branch mentioned, twice the sampling frequency is used f "sampled, which is 23.4 kHz in the example mentioned. The second sample-and-hold circuit 18 a sample taken in the middle of the disturbed interval. However, this sample is incorrect and is therefore replaced by a corresponding Value from the band-limited output signal of the low-pass filter 15 replaced, the sum of the signal delay times in the first sample-and-hold circuit 14 and the low-pass filter 15 by the delay time t of the three

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delay members 20, 21, 22 is compensated. Every sixth The sample is thus a band-limited one. Since with voice and music transmission, as already mentioned, the signal components over 5 kHz are at least 40 dB smaller than their fundamental oscillation, this sixth sample has at most one amplitude error from 1 %.

In Fig. 8, finally, some curve shapes are shown to explain the arrangement according to Fig. 7, wherein in Fig. 8a the Audio signal NF is shown sinusoidal for the sake of simplicity, which is sampled at the sampling frequency 2kf. There are those Sampling values corresponding to the sampling frequency kf with solid ordinates and the additional sampling values at double Frequency drawn dotted. At the times t .., t ", t_, which are in the middle of a tuner switchover pulse of the Duration t lie, however, no sample value of the audio signal NF can be taken.

FIG. 8b shows the band-limited output signal NF ^{1 of} the low-pass filter 15, which is delayed by the delay time t compared to the audio signal NF according to FIG. 8a. The audio signal NF ¹ is now sampled again by means of the third sample-and-hold circuit, as shown in FIG. 8c, so that now at times t. + t, t_ + t, t ₃ + t the dot-dash samples are available. These are then added by means of the changeover switch 23 to the signal occurring in the parallel branch with the circuit parts 18, 21 at the points corresponding _{to the times t ..., t "f t_.}

The arrangement according to FIG. 7 can therefore not only be used in arrangements corresponding to the first and second main patent but is generally suitable for the reconstruction of disturbed band-limited signals, if the following conditions are fulfilled: ■

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a) The duration of the disturbance T is shorter than - ^ / if f is the im

ΐ. Ill 3. X

Max

undisturbed signal is the highest frequency contained (see Fig. 9a).

b) The repetition frequency of the disturbance is less or

equal to - · f (see Fig. 9a). ο max

c) The undisturbed signal has such a spectrum that the

Signal amplitudes W at frequencies above ^ - · f opposite

- £ max

those below · = ■ · f decrease or are smaller

2 max

(see Fig. 9b).

Under the above conditions, with the arrangement according to FIG can be improved by a factor of 2.

5 sheets of drawing
with 9 figures

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Claims (3)

Claims J television receiver with a screen on which a selected first program is reproduced, and with a device by means of which another program can be reproduced on the same screen at the same time Patent (patent application P 24 13 839.4-31), whereby the Means for reproducing the further program consists of an arrangement present in the television set, which is shown in a portion of the image shown on the screen first program makes at least one image section of the further program visible and contains a memory, in which the image content to be reproduced of the further program is initially stored with a reduced number of lines and then in the corresponding position of the line of the first program to represent the further program is called up line by line, with a common signal for simultaneous playback of both programs. - ο - * Mon / Kn March 20, 1978 909839/0421 E. Zaehringer - 2 Fl 959 away (tuner, IF amplifier, video amplifier) serves and. a switching part switches the tuning means of the tuner during the lines of the picture of the further program to be stored from the reception frequency of the first program to that of the further program and according to patent ... (patent application P 25 42 502.9) the last one before the tuner starts to switch The signal value of the audio signal currently occurring on the other program is stored by means of a sample-and-hold circuit for a time which is approximately equal to the sum of the duration of the square-wave pulses switching the tuner and the settling time of the audio IF filter, the total interference duration and for this time is fed to the audio output amplifier instead of the audio signal, characterized in that the sample-and-hold circuit (14) continuously samples the audio signal (NF) at a frequency which is such an integral multiple (k) of the frequency (f ) of the square-wave pulses switching over the tuner (3) is that the hold time (t ") of the sample-and-hold circuit (14) ti remains just longer than the total duration of the malfunction (T), that the output signal (NF) of the sample-and-hold circuit (14) is continuously fed to the audio output amplifier and that the sampling signal (H) of the sample-and-hold circuit (14) and the the tuner (3) switching square-wave pulses are derived from a signal of the horizontal deflection stage (7). 2. Television receiver according to claim 1, characterized in that between the output of the sample-and-hold circuit (14) and the input of the audio output amplifier is inserted a low-pass filter (15) whose upper cutoff frequency is the same half of the sampling signal frequency (f). 3. Television receiver according to claim 2, characterized in that the low-pass filter (15) such with in the pass-through 909839/0421 E. Zaehringer - 2 Fl 959 range of constant transit time is that the audio signal (NF) is fed to a second sample-and-hold circuit (18), the sampling signal frequency (f _H o) of which is twice as large as that of the (first) sample-and-hold circuit (14 ) that the output signal of the low-pass filter (15) is fed to a third sample-and-hold circuit (19), which is fed via a first delay element (20) to the sampling signal (H2) of the second sample-and-hold circuit (18), whose The output of a second delay element (21) is connected to the normally closed contact input (231) of an electronic switch (23), to whose normally open contact input (232) the output of the third sample-and-hold circuit (19) and to whose control input (233) the tuner ( 3) switching square-wave pulses via a third delay element (22) so that the delay time (t) of the first, second and third delay element (20, 21, 22) is equal to the sum of the signal delay times in the (first) sample-and-hold circuit (14 ) and the low-pass filter (1 5) and that at the output (234) of the electronic switch (23) there is an additional low-pass filter (24), the upper limit frequency of which is twice as large as that of the low-pass filter (15). - 4th 909839/0421