JPS6184979A - Color signal processing circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a signal recording and reproducing circuit suitable for application to a magnetic recording and reproducing device, particularly a video tape recorder (hereinafter abbreviated as VTR).

[Background of the invention]

In general, the video signal recording and reproducing method in home VTRs (for example, VH8 system) uses a method in which a luminance signal is FM modulated and then frequency-multiplexed with a color signal converted to a low frequency to record and reproduce the signal. In this method, a continuous IR signal synchronized with the reproduced color synchronization signal (color burst) is generated as a means for correcting so-called jitter such as frequency fluctuation and phase fluctuation of the color signal during reproduction, and this continuous signal is used. There is a method of correcting jitter by performing frequency conversion on the reproduced color signal. ([Home VTR
Introduction J P, P.

28-32. (Yokoyama et al., 6 Corona Publishing) However, in this method, the range for correcting jitter is limited in the process of creating a continuous signal from the reproduced color synchronization signal, and there is a problem that jitter cannot be sufficiently corrected.

As a way to compensate for this problem, a color synchronization signal or a horizontal synchronization signal frequency n7m (m
, n is an integer) as a pilot signal,
A method is known in which jitter is corrected by frequency-multiplexing the pilot signal, an IFM luminance signal, and a low-frequency conversion color signal, and multiplying and frequency-dividing this pilot signal at the time of reproduction, and converting the frequency with the reproduced low-frequency conversion color signal. It is being (
(Japanese Patent Publication No. 53-45656, Japanese Patent Publication No. 49-2410) FIG. 4 shows an example of a video signal processing circuit using a biloft signal. A bypass filter (
A reproduced luminance signal y is obtained by the HPF>5 and the demodulation circuit 4. A band pass filter (BPF) is applied from the signal a.
A pilot signal d is taken out by a frequency dividing circuit 9 and a transmitting circuit 10, and a jitter correction signal q is obtained by a frequency dividing circuit 9 and a transmitting circuit 10. The jitter correction signal q is converted into a color demodulated signal by a signal g from an oscillation circuit 12 and a frequency conversion circuit (abbreviated as CONV) 11. The reproduced low-pass conversion color signal C is demodulated by the color demodulation signal at C0NV6, and a reproduced color signal 6 is obtained. During frequency conversion in C0Nv6, the jitter component included in the viroft signal d and the jitter component included in the reproduced low-pass converted color signal C cancel each other out, so that jitter can be corrected.

On the other hand, in a VH8 type VTR, recording and reproduction on a magnetic tape is performed by switching a plurality of rotating magnetic disks on a field-by-field basis. Therefore, a discontinuous point occurs in the reproduced signal at the switching point of the magnetic head. Discontinuity also occurs in the reproduced signal due to dropouts caused by scratches on the surface of the magnetic tape.

Therefore, discontinuity also occurs in the pilot signal recorded by frequency multiplexing with the video signal. Since a counter is used to frequency divide the pilot signal, a phase shift occurs in the frequency divided output at each discontinuous point. A state in which a phase shift occurs in the case of the VH8 system will be explained using diagrams.

FIG. 5 shows the pilot signal reproduced by two rotating magnetic heads (hereinafter referred to as heads) and its frequency-divided output. Connect the two heads to head 1. When the head 2 is called, a pilot signal i is obtained from the head 1, and a pilot signal k is obtained from the head 2. The divided outputs of these regenerated pilot signals are respectively 1-frequency-divided outputs j1 frequency-divided outputs j. The pilot signal reproduced by the two heads is
The signals are combined into one pilot signal by a head switching operation. This is illustrated as the biloft signal m1 frequency-divided output n. The pilot signals reproduced from the two heads do not have consecutive phases due to variations in the positional accuracy of the heads, variations in the rotational speed of the heads, etc., resulting in overlapping outputs. Therefore, the phase of the frequency-divided output n of the pilot signal m, which is a combination of these, is the frequency-divided output that should originally be output! is different from the phase of

Furthermore, since the rotational speed of the head varies, the above-mentioned phase shift also varies.

The phase shift due to dropout will be explained using FIG. 6. A frequency-divided output j is obtained from a pilot signal i without dropout. On the other hand, the division output p of the pilot signal O with dropout or dropout causes a phase shift from the normal frequency division output j in the portion where the dropout occurs.

In a jitter correction signal using a pilot signal, the phase shift that occurs in the divided output of the pilot signal becomes the phase shift of the reproduced color signal demodulated from the reproduced low-pass converted color signal, so normal color signal demodulation and jitter There was a problem that could not be corrected.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a color signal recording and reproducing circuit that can eliminate the problems of the conventional method described above and improve the S/N ratio of reproduced color signals.

[Summary of the invention]

In order to achieve the above object, the present invention utilizes the fact that a pilot signal and a horizontal synchronizing signal in a video signal have a certain phase relationship, generates a reset pulse for each horizontal synchronizing signal, and generates a reset pulse for each horizontal synchronizing signal. By resetting the counter that divides the frequency of the high-lot signal, good jitter correction can be performed that eliminates the influence of the phase shift described above.

[Example of invention]

An actual ts example of the present invention will be explained below based on the drawings. 1st
The figure is a block diagram showing an example of a signal reproducing circuit of the present invention. Components corresponding to those of the conventional example in FIG. 4 are given the same reference numerals. The difference from the conventional example in FIG. 4 is that the horizontal synchronizing signal separation circuit 16. Delay circuit 15. Differential circuit 14. The reason is that a waveform shaping circuit @13 is provided. The operation will be explained in detail below using FIG. 2. There is a certain phase relationship between the horizontal synchronization signal r separated by the horizontal synchronization signal separation circuit 16 and the pilot signal d. The horizontal synchronization signal r is sent to a delay circuit 15 in order to match the timing of the reset pulse W.
Therefore, the delayed signal S is obtained. The width of ri77tbars W is
Since the period of the high lot signal d must be smaller than the period of the high lot signal d, the differential output U of the delayed signal S is generated by the differentiating circuit 14.
After taking out the reset pulse W, the waveform shaping circuit 13 obtains the reset pulse W. Pilot signal d and reset pulse W
As shown in Figure 2, the phase relationship between the rising edge of the pilot signal that triggers the frequency divider circuit 90 counter and the next rising edge, or depending on the color/color operation, from the falling edge to the next falling edge. By selecting between the edges, it is possible to stably perform cross-sect operation of the frequency divider circuit. There is also a method of using a multivibrator to obtain the reset pulse.

Next, the principle of correcting the phase shift by resetting the frequency dividing circuit 9 will be explained using FIG. 3, taking as an example the case where a dropout occurs. As described above, when a dropout occurs in the pilot signal d, its frequency-divided output has a phase shift from the normal frequency-divided output C when there is no dropout.

If the counter of the frequency divider circuit 9 is reset by the reset pulse W, the counter will always start counting the pilot signal d for each reset pulse.
Even if a phase shift occurs due to dropout in the frequency-divided output X obtained by adding the reset pulse and the reset pulse, the phase shift is corrected after the subsequent reset pulse. Therefore, jitter correction using the high lot signal can be performed satisfactorily without being affected by dropouts or the like. The above effect can also be obtained with respect to the phase shift caused by the discontinuity of the pilot signal due to the head switching described above.

〔Effect of the invention〕

As described above, according to the present invention, the phase shift of the pilot signal frequency division output caused by the discontinuity of the pilot signal due to dropout etc. can be corrected by the reset pulse generated from the horizontal synchronization signal within the -horizontal scanning period. Can be corrected.

Therefore, the jitter correction of the reproduced color signal using the pilot signal can be performed satisfactorily, resulting in the effect of significantly and stably improving the S/N in recording and reproducing color signals.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the color signal processing circuit of the present invention, FIGS. 2 and 3 are waveform diagrams for explaining the present invention, and FIG. 4 is a reproduction signal using a conventional pilot signal. The block diagrams of the processing circuit, FIGS. 5 and 6, are waveform diagrams for explaining conventional circuits. 13...Waveform shaping circuit, 14...Differentiating circuit. 15...Delay circuit, 16...Horizontal synchronization separation circuit.

Claims (1)

[Claims] 1. Horizontal synchronization is required when dividing the frequency of a pilot signal in a magnetic recording/reproducing device that multiplexes a pilot signal with a video signal, records and reproduces it, and corrects the jitter of the reproduced video signal using the pilot signal. A color signal processing circuit characterized in that a reset pulse generated from a signal resets the operation of a frequency divider circuit at the horizontal synchronization signal period. 2. The color signal processing circuit according to claim 1, wherein the reset pulse generating means comprises a horizontal synchronizing signal separation circuit, a delay circuit, a differentiation circuit, and a waveform shaping circuit. .