FR2463558A1 - CIRCUIT FOR SYNCHRONIZING AN OSCILLATOR WITH RESPECT TO A TELEVISION SIGNAL - Google Patents

Abstract

CIRCUIT SERVING TO SYNCHRONIZE AN OSCILLATOR 7 OF A TELEVISION RECEIVER OR OF A TAPE APPARATUS FOR RECORDING TELEVISION SIGNALS AND WITH WHICH, IN ORDER TO ACCELERATE THE HANGING, THE SYNCHRONIZATION TAKES PLACE DURING THE RETURN OF THE FRAME AT DOUBLE THE LINE FREQUENCY, ON THE FREQUENCY OF THE PRE-EQUALIZATION AND POST-EQUALIZATION PULSES AND OR OF THE FRAME SYNCHRONIZATION SIGNAL INTERRUPTION PULSES. APPLICATION: TAPE APPARATUS FOR RECORDING TELEVISION SIGNALS AND TELEVISION RECEIVERS.

Description

1. "Circuit for synchronizing an oscillator with respect to

a television signal. "

  The invention relates to a circuit which, in particular

  in a television receiver or in a telephone

  for recording a television signal, synchronizes the frequency of an oscillator with respect to line frequency synchronization pulses contained in a television signal, wherein oscillation resulting from the synchronization pulses and a reference oscillation resulting from the oscillations of an oscillator are supplied to a comparator stage

  which provides the oscillator with a regulating voltage

  ge to adjust the frequency of this oscillator.

  In the case of known circuits, the synchronization is established between bs synchronization pulses separated from the

  television signal, and pulse-frequency pulses

  provided by the oscillator; the oscillator itself may oscillate at a higher frequency, for example at a frequency equal to twice the line frequency; in some band devices for recording video signals, there is an oscillator oscillating

  at a frequency of 625 kHz, that is to say at a frequency of

  the at 40 times the line frequency of 15 625 Hz, oscilla-

  whose ks impulses at line frequency are deducted

using dividing stages.

  Under certain conditions, for example when reading

  video signal recorded on a magnetic tape,

  it occurs at specific times, for example when

  that the band passes from one magnetic head to another, a little before the return frame interval, phase jumps in the position of the synchronization pulses,

  these phase jumps can last up to 16 Vs, that is to say

  say 25% of the duration of the line period. This phase jump must be eliminated quickly so that at the beginning of the next frame reproduction, the lines occupy their correct position. When said oscillator frequency

  equal to 625 kHz serves as the carrier frequency at the time of

  In the case of color signal recording, the restoration of synchronization is also essential, on the one hand, to obtain that the carrier oscillations, preferably converted at the normal frequency of 4.43 MHz (PAL system), have the phase position correct during demodulation

  colored signals and, on the other hand, to avoid

  color blemishes, for example, desaturation.

  Such possible errors are all the smaller as the time constants in the phase control circuits are small. In view of the sensitivity to the signals

  however, it is not possible to decrease

  the said constants of time. This is especially so

  1.5 for the control circuits which are incorporated into a

  television receiver connected to a recording device

  and the constants of time during reproduction

  recorded signals can not usually be

  courcies. The purpose of the invention is to accelerate, in the case of a circuit of the kind mentioned in the preamble, the phase and / or frequency adjustment in the time interval envisaged in the vicinity of the frame synchronization pulse. , this acceleration being possible without it being necessary to proceed in the circuit to changes, for example that of the time constant of a control circuit of

  frequency and / or phase, determined by a low-pass filter.

  For this purpose, the circuit according to the invention is remarkable in that during the appearance of the pulse flanks that the television signal comprises, during

  the frame return interval and whose repetition frequency

  tition is equal to a multiple of the line frequency, a phase discriminator, which at its first input receives the

  synchronization signal and whose output makes

  oscillator a frequency and / or phase adjustment voltage, receives at its second input and preferably by means of a gate circuit, a reference oscillation invariably coupled with the oscillations of the oscillator and whose repetition frequency is equal to said multiple

the line frequency.

  Because the circuit operates with a multiple (one harmonic) of the line frequency, a greater number of comparison times are available, so that an error signal can be formed more rapidly and that on the occasion of a readjustment, this signal can also be

eliminated faster.

  For this purpose, the circuit according to the invention can

  be remarkable in that at the television signal are in-

  impulse flanks whose frequency of repetition

  tition is equal to a multiple of the line frequency, for example three or four times this frequency of

  line. Such an incorporation of impulse flanks is pos-

  when recording in the case of a device

  television signal recording tape.

  It is also possible to use a traffic signal

  The normal television and the circuit according to the invention may be remarkable in that the oscillator is synchronized by at least some of the pre-equalization pulses and / or by post-equalization pulses and / or interrupt pulses. of the synchronization signal of

frame.

  The following description, with reference to the attached drawing,

  all given as an example, will make clear understanding

  the invention can be realized.

  The single figure of the drawing is a block diagram

  of a circuit according to the invention.

  A television signal containing image, suppression and synchronization signals present on a terminal

  1 is supplied to a sync pulse separation stage.

  Chronization 2. Separate sync pulses

  in this way are provided to a stage of impulse formation.

  3 in which these pulses are transformed from

  way that the output of stage 3 delivers, approximately to

  the appearance of the flanks before

  provided in the third floor, narrow impulses

  21 which have the same duration and the same amplitude. The duration of these pulses must be shorter than that of the pre-and post-equalization pulses contained in

  the frame deletion pulse, the duration of said

  pulses being equal to half of that of the line pulses; in the case of a television signal conforming to the OCIR standard, the duration of these forward edge pulses at the output of the stage 3 is thus less than 2.3 us. These

  pulses 21 are provided at a first input 5 of a dis-

  Phase 4 Criminator whose second entry 6 receives

  pulses 22 which have the line frequency and which,

  oscillator 7 are provided at input 6 of the

  criminator 4 through a first frequency divider 8

  and a second frequency divider 9 connected behind the-

  said first frequency divider 8, as well as through the

  first working contact and the central contact of a com-

  mutator 11. The adjustment voltage which occurs at the output terminal 13 of the discriminator 4 is supplied to the oscillator 7 adjusting input through a low-pass filter 14 containing at least one time-constant element. In the circuit envisaged, the phase position of the oscillator 7 is compared at times separated by a line period, at the synchronization signals applied 21, and this gives

to a setting voltage.

  According to the invention, during the appearance of the pulse flanks with a high repetition frequency

  in the vicinity of the frame pulse, it is supplied to the

  criminator 4 a comparison oscillation having the frequency

  quence double, which gives rise to a comparison of the

  phase position and to obtain a control voltage-

  at moments separated by a half-period of line. For this purpose, in the time interval during which the pulse flanks 21 at a frequency equal to twice the line frequency occur in the television signal applied, the switch 11 leaves its home position to acquire its home position. job. With the aid of a gate circuit 12,

  said time interval is detected in the traffic signal.

  the television, and a corresponding signal is provided to the switch 11. Using the first frequency divider 8 and the

  second frequency divider 9, the oscillation frequency

  oscillator 7, for example equal to 625 kHz, is divided by 40 to thereby obtain the line frequency equal to 15 625 Hz. The second frequency divider 9 divides by two the frequency obtained by the first divider 8, which is a divisor by twenty. In this way, it is possible to take from the output of the first frequency divider 8 an oscillation in the form, for example, of pulses of which

  the frequency is equal to twice the line frequency.

  In the working position of the switch 11, said discriminator

  phase 4 therefore receives comparison oscillations

  23 at a higher frequency, so that each flank with frequency

  quence equal to twice the line frequency and present in the television signal, is used to adjust the frequency of the oscillator 7. As a result, the readjustment

  of this oscillator is accelerated significantly.

  In the case where the invention is used for the synchronization of lines in a television receiver, the frequency of the oscillator 7 is equal to twice the

  Line frequency and divider 8 is not necessary.

  In this case, the switch 11 then switches between the input

  and the output of the divider by two 9.

  In the case of a tape device for recording a television signal, the signal can be modified during recording, so that it contains pulse flanks whose repetition frequency is a multiple of the line frequency, for example equal to 3 times or 4 times thereof. Such a signal is thus inserted in the vicinity of the frame synchronization signal, somewhere between the last frame of a frame and the frame.

  first line of image of the following frame.

Claims (5)

  1.- Circuit which, especially in a receiver of   television or in a tape device for recording   television signal, synchronizes the frequency of an oscillator with respect to   line frequency synchronization contained in a   television channel, a circuit in which an oscillation de-   synchronization pulses and a reference oscillation derived from the oscillations of an oscillator   are supplied to a phase comparator stage which furnishes   to the oscillator a tuning voltage for adjusting the frequency of this oscillator, characterized in that during the appearance of pulse flanks that includes the television signal during the frame return interval and 1.5 of which the repetition frequency is equal to a multiple of the line frequency, a phase discriminator, which at its first input receives the synchronization signal and   whose output delivers an oscillating voltage to the oscillator   frequency and / or phase frequency, receives at its second   and preferably using a gate circuit, an oscillator   reference lation invariably coupled with the oscilla-   oscillator and whose repetition rate   is equal to said multiple of the line frequency.   2. Circuit according to claim 1, characterized in that the television signal is incorporated pulse flanks whose repetition frequency is equal to a multiple of the line frequency, for example three times   or four times that line frequency.   3. Circuit according to claim 2, characterized in   what in the case of a tape device for recording   of a television signal, pulse flanks whose repetition frequency is equal to a multiple of   line frequency are added during recording.   4. Circuit according to any one of the claims   1 to 3, characterized in that the oscillator is synchronized by at least some of the pre-equalization pulses and / or by post-equalization pulses and / or by interrupt pulses of the frame synchronization signal . 5. Circuit according to claim 4, characterized in that the line pulses are derived from the signals of the oscillator by frequency division, and that the oscillations used for the synchronization and whose repetition frequency is equal to twice the frequency   of the line are taken from the penultimate floor of in two.