FR2608880A1 - SYSTEM FOR EXTRACTION AND MEASUREMENT OF AMPLITUDE OF SYNCHRONIZATION SIGNALS IN TELEVISION RECEIVERS, PARTICULARLY FOR SATELLITE TRANSMISSION - Google Patents

Abstract

THE SYSTEM INCLUDES A SYNCHRONIZATION PULSES EXTRACTION 3 CIRCUIT WHICH INCLUDES A COMPARATOR 21 WITH A REFERENCE LEVEL 5 WHICH VARIES WITH THE AMPLITUDE OF THE SYNCHRONIZATION SIGNAL OBTAINED FROM AN AMPLITUDE MEASURING CIRCUIT 2 WHICH INCLUDES A PAIR OF SAMPLERS 6, 7 FREQUENCY HANGS TO THE SYNCHRONIZATION SIGNAL EXTRACTED BY THE EXTRACTION CIRCUIT 3 AND A DIFFERENTIAL AMPLIFIER 12 SERVING TO CALCULATE THE AMPLITUDE OF THE SYNCHRONIZATION SIGNAL BY CALCULATING THE DIFFERENCES BETWEEN THE DIFFERENCES SAMPLERS 6, 7.

Description

The present invention relates to an extraction and measurement system

  amplitude of the synchronization signals in the

  television transceivers, especially for trans-

satellite missions.

  In receiver-transmitter signal systems

  television, especially if the signals are transmitted by satellite

  lite, iL is necessary to extract both

  synchronization signals only with the measurement of their amplitude.

  Extraction of synchronization signals is necessary.

  to synchronize the different circuits that process the television signal (timers, spreading signal generators, latching and locking circuit, circuits for

  the insertion and extraction of the sound which is superimposed on the synchro-

  nizations). The measurement of the amplitude of the timing signals is necessary to obtain information concerning the level of the television signal and thus to supply possible alarm signals. As is well known, a television signal has a peak-peak value which varies with its information content: the maximum level corresponds to white, the minimum level corresponds to black. On the contrary, the value of the synchronization signals does not vary with the information content, but it only varies

  if the general level of the television signal actually varies.

  It follows that correct information on the level of the television signal can be obtained by measuring the amplitude of the

synchronization signals.

  To achieve this, it is necessary to use a

  sampling system, in which of the sampling intervals

  are attached to the extracted synchronization signals.

  Extraction of synchronization signals is normal-

  ment carried out using a diode locking circuit,

  followed by a comparator and a timer.

  The comparison is performed against a fixed reference value. This results in a significant reduction in noise immunity in the comparison, in the case where a signal is received

  TV with a very low S / N signal-to-noise ratio.

  this is the case for reception from satel-

  lites, o, with stations of the INTELSAT STANDARD B type, it is possible that the signal received at the received frequency has a very low carrier / noise C / N ratio, to the point of arriving near the system operating threshold. Under these conditions, the signal / noise ratio S / N is below the standard values set by international standards and the signal extraction system.

  synchronization, working by comparison with a reference

  fixed reference, can therefore make inadmissible errors.

  In other words, it is not possible to use

  such systems for situations close to reception threshold.

  The measurement of the amplitude of the synchronization signals is in turn carried out in general separately from the extraction, by

  simple sampling of the peak (or trough) level of the pulse

  synchronization, after setting the reference, given

  by the suppression level (or maximum level at the end of the pulses

sions) to the value of 0 volts.

  This reference can however be affected by thermal drifts or due to the supply voltage, drifts which can

  deteriorate the correction of the measurement.

  In addition, the measurement method described above is not applicable in the presence of S.I.S., that is to say a sound superimposed on the synchronization signals. Indeed, in such a case, the measured level would be affected by amplitude modulations under

  the effect of modulations due to the audio channel.

  The object of the present invention is therefore to produce a

  system for extracting and measuring amplitude of syn-

  chronization which is free from the aforementioned drawbacks and which makes it possible in particular to obtain an optimal comparison during the extraction phase, both in the presence of a reduction in the level of

  TV signal only in the presence of increased noise.

  According to the invention, this object is achieved with a system

  for extracting and measuring the amplitude of synchronization signals

  sation which includes an extraction circuit and a measurement circuit

260O8880-

  amplitude, said extraction circuit comprising a locking circuit, a comparator and a timer and said amplitude measurement circuit comprising at least one sampler hooked in frequency to the synchronization signal, characterized in that said comparator is provided with '' a reference level which varies with the amplitude of the synchronization signal, and which and

  supplied by the amplitude measurement circuit.

  Also according to the invention, the amplitude measurement circuit comprises a first sampler and a second sampler controlled by the extraction circuit so as to carry out the sampling at the level of the trough and, respectively, at the level of suppression of the signals of frame synchronization, - means being provided for calculating the amplitude of the synchronization signals by forming the difference between the two levels

sampled.

  The attachment of the reference level of the comparator of the

  extraction circuit for amplitude measurement of syn-

  chronization, which is carried out by double sampling of

  frame synchronization signals, provides a compa-

  right under optimal conditions, both in the presence of a reduction in the television signal level and in the presence of a

increased noise.

  This results in better immunity to noise introduced by the satellite-receiver path, that is to say that it makes it possible to operate under conditions of very low C / N ratio, at

  near the receiver operating threshold.

  This means that even under such critical conditions

  ticks, it is possible to have correct alarm information of the television signal and to correctly control the extraction circuit, so as to eliminate from the television signal the

  scatter signal introduced into the transmission.

  Finally, the system according to the invention is able to function

  even in the presence of S.I.S. This is achieved by advantageously delaying the sampling of the trough level of the frame synchronization signals, in order to carry out the measurement.

  of said dip level in an area free of S.I.S.

260 888 0

  Other characteristics and advantages of the invention

  will be better understood on reading the description which follows

  of an exemplary embodiment and with reference to the accompanying drawings, in which: FIG. 1 represents the block diagram of said preferred embodiment of the system according to the invention; FIGS. 2a to 2f represent a series of graphs representative of the shape of the signals at different points in the system of FIG. 1; Figures 3 to 5 show applicable extensions of

Figure 1 system.

  The system for extracting and measuring the amplitude of the synchronization signals which is illustrated and designated as a whole by the reference numeral 1 in FIG. 1 is composed of an amplitude measuring circuit 2 and a circuit d 'extraction

  3, interconnected with each other and supplied by the tele-signal

  TV vision arriving from a receiving terminal 4, through an amplifier

  band eliminator 5, which brings the signal to the optical level

  bad for the following treatments and eliminates from this signal the under-

  carrier of chrominance (of a frequency of 4.43 MHz for the

  standard 625 lines, or 3.58 MHz for the standard 525 lines).

  The amplitude measurement circuit 2 includes two samples

  tillonners 6 and 7, constituted by electronic switches

  8 and 9 fitted with holding capacitors 10 and 11. The sample-

  neur is therefore of the sampling and maintenance type.

  The outputs of samplers 6 and 7 are respective-

  connected to the negative or inverting input and to the positive or non-inverting input of a differential amplifier 12 provided with an output integrator 13 formed of a resistor 14 and a

  capacitor 13 in parallel with each other towards ground.

  The output signal A constitutes the measurement of the amplitude of the synchronization signals and it is supplied on a terminal of

exit 16.

  The extraction circuit 3 in turn comprises a locking circuit 17 formed of a capacitor 18 and a diode 19 connected in series. Across diode 19, which is polarized

  directly, there is a voltage Vd which fixes the trough of the impuL-

  synchronization sions at the output 20 of the latching circuit 17 at the voltage value -Vd. This value will be chosen so as to be approximately equal to half the total level of the television signal. In this way, the output voltage 5 of the circuit

  snap 17 will oscillate between the values + Vd and -Vd.

  The output 20 of the locking circuit 17 is connected to the negative input of a comparator 21, the positive input of which is connected to the output of the differential amplifier 12 via an attenuator 22. The signal thus taken from the measurement circuit of amplitude 2 constitutes the reference threshold R for the comparator 21. If we consider the choice made for the voltage Vd, this threshold will, under nominal conditions, be approximately at the center of the signal interval, c that is, approximately equal to 0 V, while it goes up and down with the increase and decrease of the maximum level of the synchronization signal. More precisely, if the signal decreases, the maximum or suppression level also drops, while the minimum or trough level remains fixed at - Vd; in such a case, the reference level R also goes down, but while still remaining at the center of the interval

signal amplitude.

  The output of comparator 21 is connected to a terminal 23, on which therefore appear the synchronization signals B

  suitably put on square waves.

  The output of comparator 21 is further connected to a timer 24, which controls two monostable multivibrators 25 and 26, respectively assigned to the control of the samplers 7

  and 6 of the amplitude measurement circuit 2.

  The monostable 25 is active in coincidence with the rising edge of the timer 24 output signal. The monostable 26 is in turn active in coincidence with the falling edge of the timer 24 output signal. The latter is finally chosen so that the falling edge of its output signal coincides with the trough level of the frame synchronization pulses, with a predetermined delay with respect to the start of said trough level, and so that the rising edge coincides with its

  turn with the level of suppression of synchronous pulses

  station. It derives therefrom the following operating mode of the system represented in FIG. 1. To describe it, we will refer to

graphics in Figure 2.

  The TV signal, amplified and freed from the chrominance subcarrier in amplifier 5, reaches the

  extraction circuit 3 and to the amplitude measurement circuit 2.

  At each line or frame synchronization pulse, the diode latch circuit 17 provides at its output the

  signal S represented in graph a) of FIG. 2, that the com-

  parateur 21 then compares with the reference signal R, in

  giving origin to the square signal of the graph b) of figure 2.

  As already said, the reference signal varies with the amplitude of the synchronization signal, which is measured by the measurement circuit 2, so that the operating threshold of the comparator is always maintained at the center of the amplitude interval of the synchronization signal. We can thus obtain an optimal comparison, even with a very small S / N ratio. The

  square signal B obtained at the output represents the extracted pulse.

  Timer 24 delays its own activation by

  prefixed time T with respect to the falling edge of each pulse

  square sion appearing at the output of comparator 21, so as to isolate the frame synchronization signals (of longer duration) from the line synchronization signals (of shorter duration) and to further work in an area of the frame pulses which is free from so-called SIS signals (its superimposed on the synchronizations), located in the initial part of the level of the trough of the synchronization pulses. The succession of a line synchronization signal SR and an image synchronization signal SQ is illustrated in graph c) of FIG. 2,

  while the corresponding signal appearing at the time output

  porizer 24 is illustrated in graph d) of this same

figure 2.

  This last signal controls the two monostables 25 and 26,

  each of which generates a pulse of duration equal to 2.5 micro-

  seconds, which are respectively in coincidence with the rising edge and the falling edge of the incoming signal, as we have

  shown in graphs e) and f) in Figure 2.

  The monostable 26 controls the sampler 6, which performs the minimum level or trough Lm sampling of the signal

frame synchronization.

  The monostable 25 in turn controls the sampler 7, which in turn performs the sampling of maximum level or

  LM suppression of the same frame synchronization signal.

  In amplitude measurement circuit 2, the amplifier

  differential 12 calculates the difference between the two exchange values

  staggered by giving the output signal A which is representative of the amplitude of the synchronization signal, and by correcting each time the reference level R of comparator 21 of the circuit

extraction 3.

  The fundamental system 1 of FIG. 1 can be the subject of different extensions, as shown on

Figures 3 to 5.

  In particular, it can be associated with a circuit 31 for the

  suppression of the dispersion signal introduced during the trans-

  mission. This added circuit comprises a locking switch 32 controlled by a timer 33, which receives the square signal obtained at the output of the comparator 21 of the extractor circuit 3 of the basic system 1. The time is chosen so as to carry out the sampling in coincidence with the rear bearing level which follows the rising edge of the line synchronization pulses. An amplifier 34 is also provided in cascade with

  the band elimination amplifier 5.

  In order to further increase immunity to noise and

  tuels phenomena of time base instability, even in the presence of reduced level of the television signal, it is on the other hand

  possible to associate a circuit which performs a second comparison

  sound, always with a moving reference, i.e. a reference

  automatically attached to the synchronization signals.

  Said added circuit is illustrated and designated by 41 in FIG. 4, and it includes a comparator 42, a timer 43 and an attenuator 44, which receives the amplitude measurement signal

  A produced by the measurement circuit 2 of the fundamental system 1.

  The circuit 41 is free from the problems associated with the drifts of the diode 19 and it can therefore make it possible in certain cases to obtain extractions of synchronization signals (signal C) still

  better than those that can be obtained with the basic system

mental 1.

  Finally, as shown in FIG. 5, provision can be made for the combination of circuits 1, 31 and 41, the

  last pilot a lock switch 45 placed in derivative

  tion with respect to a transmission line of the tele-

  vision which plugs into the receiving terminal 4 thanks to a circuit

  bypass 46 which includes two amplifiers 47 and 48.

  In the latter case, the circuit 1 is a basic circuit for extracting and measuring the synchronization signals, the circuit 31 performs the hooking in coincidence with the rear bearing level to obtain a first suppression of the dispersion signal or d spreading and the circuit 41 eliminates the dispersion signal by means of another locking circuit,

  and performs a second mobile reference comparison.

  Of course, various modifications may be made.

  those skilled in the art to the device which has just been described in

  by way of example without departing from the scope of the invention.

Claims (10)

  1. System for extracting and measuring amplitude of synchronization signals in television receiver-transmitters, comprising an extraction circuit (3) and an amplitude measuring circuit (2), said extraction circuit (3) including a   locking circuit (17), a comparator (21) and a time delay   tor (24) and said amplitude measurement circuit (2) comprising at least one sampler (6, 7) hooked in frequency to the synchronization signal, characterized in that said comparator (21) is provided with a reference level (R) which varies with the amplitude of the synchronization signal, supplied by the measurement circuit amplitude (2).   2. System according to claim 1, characterized in that said amplitude measurement circuit (2) comprises a first and a second sampler (6, 7) controlled by the extraction circuit (3) so as to perform respectively l of frame synchronization pulses for the trough level and, respectively, for the blanking level, means (12)   being provided for calculating the amplitude of the synchronization pulses   sation by forming the difference between the two levels sampled   given. 3. System according to claim 2, characterized in that   that said means (12) for calculating the amplitude are made   by a differential amplifier (12) having inputs   which are connected to the outputs of said samplers (6, 7).   4. System according to claim 2, characterized in that said samplers (6, 7) are of the sampling and holding type. 5. System according to claim 3, characterized in that said reference level (R) of the comparator (21) of the extraction circuit (3) is provided by the output of said amplifier differential (12).   6. System according to claim 2, characterized in that said timer (24) of the extraction system (3) controls, in succession over time, a first and a second multivibrator 260 888 0   monostable (26, 25) which are respectively assigned to the control of the first and of the second sampler of the amplitude measurement circuit (2), said timer (24) being chosen so as to activate said first multivibrator (26) in coincidence with the trough level of the frame synchronization pulses and said   second multivibrator (25) coinciding with the level of sup-   pressure of frame synchronization pulses.   7. System according to claim 6, characterized in that said timer (24) is chosen so as to activate said first multivibrator (26) with a predetermined time delay relative to the falling edge of the synchronization pulse weft.   8. System according to claim 1, characterized in that the output of said comparator (21) from the extraction circuit (3) is adapted to drive a circuit (31) intended for the suppression of the dispersion signal which is introduced during the transmission, said suppression circuit (31) comprising a locking switch (32) controlled by said comparator output (21)   via a timer (33).   9. System according to claim 1, characterized in that the output of said amplitude measurement circuit is used as a variable reference level for a comparator (42) belonging to another extractor circuit (41) which works in parallel with said extraction circuit (3).   10. System according to claim 9, characterized in that the output of said other extractor circuit (41) controls another locking switch (45) placed in parallel with respect to   a television signal transmission line.