GB1575776A - Method for the remote synchronization of a colour television synchronizing generator in accordance with ccir-pal standards - Google Patents

Abstract

The burst from the remote FBAS signal is separated via a burst strobe (1) and fed to a first phase comparator circuit (2). The regulating voltage of this first phase comparator circuit controls a first reference oscillator (4). The synchronisation signal contained in the FBAS is diverted by an amplitude filter, and separated into its horizontal and vertical components by separators (7) and (10). In a second phase comparator circuit (12), the horizontal pulse (11) from the horizontal separator (10) is compared with an internal horizontal pulse (14) received from a divider (17). The regulating voltage which is derived in this way controls a second reference oscillator (13), which oscillates at double the horizontal frequency (2fH), and provides clock pulses for the divider (17). The synchronisation pulses generated in the divider are fed to the picture signal sources to be synchronised via a transit time compensator (18). The divider (17) is set by a reset pulse (15) which is gained from a reset pulse circuit (9). The colour television clock generator can be perfectly synchronised even by semi-professional video recorders, which usually leads to unsatisfactory results because of timing errors and dropouts. It is also possible to implement a short synchronisation time. <IMAGE>

Description

(54) METHOD FOR THE REMOTE SYNCHRONIZATION OF A COLOUR TELEVISION SYNCHRONIZING GENERATOR IN ACCORDANCE WITH CCIRPAL STANDARDS (71) We, GRUNDIG E.M.V. ELEK TRO-MECHANISCHE VERSUCHS- ANSTALT MAX GRUNDIG a German Corporate Body of Kurgartenstrasse 37, D--8510 Fuerth, Germany, 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: The invention relates to a method for the remote synchronization of a colour television synchronizing generator in accordance with CCIR-PAL standards.

If various FBAS signals are to be mixed with one another, then it is necessary to operate the FBAS signal sources in synchronism. The synchronization of these picture-signal sources is generally effected from a synchronizing generator centre which delivers the appropriate synchronizing signals.

If semi-professional video recorders (which cannot be horizontal-frequency synchronized because of their excessive time error) or the public television network are used as FBAS signal sources, then the synchronizing generator centre must itself be able to be remotely synchronized. In this case, the synchronization of the synchronizing generator centre is effected through the public television network or the video recorder, while the picture-signal sources are synchronized through the synchronizing generator centre.

In known arrangements for black-and-white television installations, the incoming synchronizing signal is compared with an inr ternally derived, horizontal-frequency pulse train in a phase discriminator provided for this purpose and the regulating voltage is used for the further control ob the internal timingfrequency oscillator. Thus phase equality of the horizontal-frequency pulses is achieved.

For the vertical synchronization, either a phase comparison of the vertical-frequency pulses is carried out, with corresponding influence of the timing frequency, or the vertical counter is set by a vertical-frequency pulse obtained from the synchronizing signal.

These methods cannot, however, simply be transferred to colour television installations, because here there must also be the correct phase position for chrominance carrier and PAL switching voltage.

The object of the invention is to provide a simple system for the synchronization of a PAL colour television synchronizing generator, wherein the correct correlation in time is assured for horizontal and vertical frequency and also for chrominance carrier and PAL switching phase.

This invention provides a method for the remote synchronization of a colour television synchronizing generator in accordance with CCIR-PAL standards, in which an FBAS signal is used for the synchronization, in which horizontal and vertical pulses as well as burst are separated out of such an FBAS signal, in which burst and horizontal pulses are used to control reference oscillators through phase comparison circuits, which reference oscillators produce respectively the chrominance carrier and double the horizontal frequency from which are derived, through a frequency divider, synchronized horizontal and vertical pulses, and in which the frequency divider is set by a specially obtained reset pulse which contains the information for the correct field correlation and also for PAL switching phase.

This invention also provides a circuit for the remote synchronization of a colour television synchronizing generator in accordance with CCIR-PAL standards, comprising an input for an FBAS signal, means for separating out horizontal and vertical pulses and burst from said FBAS signal, reference oscillators arranged to be controlled by the burst and horizontal pulses through phase comparison circuits, said reference oscillators being arranged to produce respectively the chrominance carrier and double the horizontal frequency from which are derived, through a frequency divider, synchronized horizontal and vertical pulses, and means for producing a special reset pulse, containing the information for the correct field correlation and for PAL switching phase, said reset pulse being arranged to set the frequency divider.

The particular advantage of the invention in comparison with the prior art is to be seen in the fact that by suitable construction of the horizontal phase comparison and of the circuit arrangement for obtaining the reset pulse, the colour television synchronizinggenerator centre can also be satisfactorily synchronized by semi-professional video recorders, which normally only leads to unsatisfactory results because of the time errors and drop-outs.

Embodiments of this invention will now be delscribed, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a block circuit diagram of a circuit for carrying out the method according to the invention; Figure 2 shows an example of a circuit for obtaining a special reset pulse; Figure 3 shows pulse diagrams to explain the circuit of Figure 2; Figure 4 shows an example of a circuit for equalizing the transit time of the FBAS signal synchronizing the centre; and Figure 5 shows pulse diagrams for the circuit of Figure 4.

According to the circuit of Figure 1, illustrated as a block circuit diagram, the burst is separated out of an FBAS signal through a burst gate 1 and supplied to a first phase comparison circuit 2, the regulating voltage of which controls a first reference oscillator 4. In addition, the synchronizing signal S contained in the FBAS signal is provided at 6 by means of an amplitude filter 5 and then split into its vertical and horizontal components by separators 7 and 10. The horizontal pulse H at 11, obtained by means of the H-separator 10, is compared with an internal horizontal pulse 14 taken off from a divider 17, in a second phase comparison circuit 12. The regulating voltage obtained in the course of this controls a second reference oscillator 13 which oscillates at double the horizontal frequency 2 fH and delivers the timing pulses for the divider 17.

All the pulses necessary for synchronizing picture-signal sources are produced in the divider 17 by frequency division and logical combination. The synchronizing pulses thus obtaned are then supplied to the various picture-signal sources to be synchronized, via a transit-time equalization means 18.

The various transit times of the synchronizing and FBAS signals, depending on the cable length are compensated for by this transittime equalization means 18, in such a manner that all synchronizing signals for picturesignal sources with shorter cable lengths are delayed according to the delay for the longest cable length. Therefore, all FBAS signals of the synchronized picture-signal sources have a difference in delay in comparison with the synchronizing FBAS signal, which is equalized by delay of the synchronizing FBAS signal in order to ensure a satisfactory mixing of all FBAS signals.

The expenditure on circuitry for the delay of a video signal is not inconsiderable, however, and can only be effected through correspondingly broad-band delay lines. In order to avoid this, a delay equalization 19 is introduced into the supply line for the internal horizontal pulse taken off from the divider 17 to the second phase comparison circuit 12.

This can be effected in a simple manner by means of integrated circuits.

With an appropriately delayed pulse, the effect is achieved that the timing frequency 2 fH and hence all the output signals of the divider 17 lead the horizontal pulse 11 or the synchronizing FBAS signal by an adjustable value.

In order to ensure the correct field correlation and the correct PAL switching phase, the divider 17 is set by a special reset pulse 15 which is obtained in a reset-pulse circuit 9. One example of an embodiment of such a reset-pulse circuit 9 can be built up with integrated switching circuits as shown in Figure 2.

For the selection of the reset pulse 15, the frequency of the horizontal pulse 11 is first divided with a 1:2 divider 21, the 1:2 divider 21 being set by the PAL switching voltage 3 derived from the burst 40. The output pulses at half the horizontal frequency are supplied, through a pulse shaper 22, to a coincidence gate 25 and compared with a verticalfrequency pulse 23 which is obtained by integration of the synchronizing signal 6 and pulse shaping through a monostable multivibrator 30. As a result of the nature of the logical combination, coincidence is only possible after every fourth field (Figure 3). This has to mean that the coincidence gate 25 only delivers an output pulse in the field 1, 5, 9 etc.

Since the divider 17 begins the pulse counting at the moment t2 of the field 2, it must also be set by a pulse which corresponds to this field. Accordingly, a flip-flop 26 is set by the output pulse of the coincidence gate 25, which is produced at the moment t, of the field 1, which flip-flop then releases a 1:155 divider 28. After 155 pulses at half the horizontal frequency, this divider 28 delivers an output pulse at the moment t2, which output pulse delivers the reset pulse 15 at a quarter of the vertical frequency through a pulse shaper 29. The 1:155 divider 28 is blocked via the flip-flop 26.

In order to prevent disturbances in the synchronizing FBAS signal, for example drop-outs in video recorders, from leading to a false selection of the reset pulse. 15, the coincidence gate 25 is blocked by a vertical pulse 16 taken off from the divider 17. Thus a reset pulse. 15 is produced when an input to gate 25 is provided from pulse shaper 22 once the vertical pulses of the synchronizing FBAS signal and of the divider 17, have become out of phase.

Finally, Figure 4 shows a circuit arrangement for the delay equalization in which the internal horizontal pulse 14 is differentiated through a capacitor 31 or an inverter 30 and a capacitor 32 and supplied to an AND-gate 33. A monostable multivibrator 35 is triggered by the pulses 34 appearing at the output of the AND-gate 33. The output pulses 36 of the monostable multivibrator time a flipflop 38 which is set by the negative edge of the input signal so that a correspondjngly delayed signal is taken off at the ouput Q of this flip-flop. The delay which can be achieved is variable by adjusting a time-determining resistor 37 connected to the monostable multivibrator 35. The correlation of the individual pulses in time is illustrated in Figure 5.

WHAT WE CLAIM IS: 1. A method for the remote synchronization of a colour television synchronizing generator in accordance with CCIR-PAL standards, in which an FBAS signal is used for the synchronization, in which horizontal and vertical pulses as well as burst are separated out of such an FBAS signal, in which burst and horizontal pulses are used to control reference oscillators through phase comparison circuits, which reference oscillators produce respectively the chrominance carrier and double the horizontal frequency from which are derived, through a frequency divider, synchronized horizontal and vertical pulses, and in which the frequency divider is set by a specially obtained reset pulse which contains the information for the correct field correlation and also for PAL switching phase.

2. A method as claimed in Claim 1 in which, for the selection of the special reset pulse, first the horizontal pulses derived from the synchronizing FBAS signal are divided by a 1: 2 divider (21), which 1: 2 divider is set by a switching voltage derived from the burst, in which the output of this 1:2 divider is connected, through a monostable multivibrator working as a pulse shaper, to one input of a coincidence gate to the second input of which a vertical-frequency pulse is supplied which is obtained by integration of the synchronizing signal separated out of the synchronizing FBAS signal after pulse shaping via a monostable multivibrator, in which the output of this coincidence gate is connected to the timing input of a flip-flop which sets a 155 counter, in which the timing input of this counter is connected to the output of said 1:2 divider and in which the output of the 155 counter is connected to the reset input of the flip-flop and the timing input of a pulse shaper.

3. A method as claimed in Claim 2, in which a vertical-frequency blocking pulse is supplied to a third input of the coincidence gate.

4. A method as claimed in Claim 1, in which, in order to equalize the transit time of the synchronizing FBAS signal, the in ternal horizontal pulse supplied to a phase comparison circuit is correspondingly delayed.

5. A method as claimed in Claim 4, in which needle pulses are produced from lead ing and trailing edge of the pulse to be delayed, by differentiation, which needle pulses trigger a monostable multivibrator, the output of which is connected to the timing input of a flip-flop which is set by the negative edge of the input signal.

6. A method as claimed in Claim 1 and substantially as herein described.

7. A circuit for the remote synchronization of a colour television synchronizing generator in accordance with CCIR-PAL standards, comprising an input for an FBAS signal, means for separating out horizontal and vertical pulses and burst from said FBAS signal, reference oscillators arranged to be controlled by the burst and horizontal pulses through phase comparison circuits, said reference oscillators being arranged to produce respectively the chrominance carrier and double the horizontal frequency from which are derived, through a frequency divider, synchronized horizontal and vertical pulses, and means for producing a special reset pulse, containing the information for the correct field correlation and for PAL switching phase, said reset pulse being arranged to set the frequency divider.

8. A circuit as claimed in Claim 7, and substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. a false selection of the reset pulse. 15, the coincidence gate 25 is blocked by a vertical pulse 16 taken off from the divider 17. Thus a reset pulse. 15 is produced when an input to gate 25 is provided from pulse shaper 22 once the vertical pulses of the synchronizing FBAS signal and of the divider 17, have become out of phase. Finally, Figure 4 shows a circuit arrangement for the delay equalization in which the internal horizontal pulse 14 is differentiated through a capacitor 31 or an inverter 30 and a capacitor 32 and supplied to an AND-gate 33. A monostable multivibrator 35 is triggered by the pulses 34 appearing at the output of the AND-gate 33. The output pulses 36 of the monostable multivibrator time a flipflop 38 which is set by the negative edge of the input signal so that a correspondjngly delayed signal is taken off at the ouput Q of this flip-flop. The delay which can be achieved is variable by adjusting a time-determining resistor 37 connected to the monostable multivibrator 35. The correlation of the individual pulses in time is illustrated in Figure 5. WHAT WE CLAIM IS:

1. A method for the remote synchronization of a colour television synchronizing generator in accordance with CCIR-PAL standards, in which an FBAS signal is used for the synchronization, in which horizontal and vertical pulses as well as burst are separated out of such an FBAS signal, in which burst and horizontal pulses are used to control reference oscillators through phase comparison circuits, which reference oscillators produce respectively the chrominance carrier and double the horizontal frequency from which are derived, through a frequency divider, synchronized horizontal and vertical pulses, and in which the frequency divider is set by a specially obtained reset pulse which contains the information for the correct field correlation and also for PAL switching phase.

2. A method as claimed in Claim 1 in which, for the selection of the special reset pulse, first the horizontal pulses derived from the synchronizing FBAS signal are divided by a 1: 2 divider (21), which 1: 2 divider is set by a switching voltage derived from the burst, in which the output of this 1:2 divider is connected, through a monostable multivibrator working as a pulse shaper, to one input of a coincidence gate to the second input of which a vertical-frequency pulse is supplied which is obtained by integration of the synchronizing signal separated out of the synchronizing FBAS signal after pulse shaping via a monostable multivibrator, in which the output of this coincidence gate is connected to the timing input of a flip-flop which sets a 155 counter, in which the timing input of this counter is connected to the output of said 1:2 divider and in which the output of the 155 counter is connected to the reset input of the flip-flop and the timing input of a pulse shaper.

3. A method as claimed in Claim 2, in which a vertical-frequency blocking pulse is supplied to a third input of the coincidence gate.

4. A method as claimed in Claim 1, in which, in order to equalize the transit time of the synchronizing FBAS signal, the in ternal horizontal pulse supplied to a phase comparison circuit is correspondingly delayed.

5. A method as claimed in Claim 4, in which needle pulses are produced from lead ing and trailing edge of the pulse to be delayed, by differentiation, which needle pulses trigger a monostable multivibrator, the output of which is connected to the timing input of a flip-flop which is set by the negative edge of the input signal.

6. A method as claimed in Claim 1 and substantially as herein described.

7. A circuit for the remote synchronization of a colour television synchronizing generator in accordance with CCIR-PAL standards, comprising an input for an FBAS signal, means for separating out horizontal and vertical pulses and burst from said FBAS signal, reference oscillators arranged to be controlled by the burst and horizontal pulses through phase comparison circuits, said reference oscillators being arranged to produce respectively the chrominance carrier and double the horizontal frequency from which are derived, through a frequency divider, synchronized horizontal and vertical pulses, and means for producing a special reset pulse, containing the information for the correct field correlation and for PAL switching phase, said reset pulse being arranged to set the frequency divider.

8. A circuit as claimed in Claim 7, and substantially as herein described with reference to the accompanying drawings.