JPH0681334B2 - Sync signal separation device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sync signal separation device for extracting a sync signal used for signal processing when a video signal recorded on a magnetic tape or the like is reproduced from the video signal.

Conventional technology Conventionally, when recording and reproducing a video signal on a magnetic tape or the like, a composite signal such as NTSC is separated into a luminance signal and a modulation color difference signal, and the luminance signal is FM-modulated and converted to a low frequency. A so-called low frequency conversion system is used in which a modulated color difference signal is mixed and recorded and reproduced.

However, there are problems such as cross-modulation and phase noise of color difference signals, and they are not suitable for high-quality recording and reproduction. Therefore, three signals of the luminance signal and the two color difference signals are time-axis compressed,
(Japanese Patent Laid-Open No. 53-109423), a method of FM-modulating it and recording / reproducing can be considered.

The problem to be solved by the present invention is that, when such a signal is reproduced and demodulated and restored to the original three signals, if the reproduced signal contains jitter, the restored signal appears as a double of the expansion rate. . Also, it is stored in the memory at the time of decompression, but at this time, if a demodulation synchronization signal is used as a reference signal for setting the start address and clock generation,
The jitter of the restored signal has a great influence on the SN ratio of the synchronization signal.
Also, during FM modulation, the sync signal is located at the lower frequency side, and the falling edge of the sync signal is located at a lower frequency due to the pre-emphasis circuit, which easily causes carrier leakage during demodulation. , High SN ratio cannot be expected. Therefore, it is difficult to reduce the jitter of the restored signal when the demodulation synchronization signal is used for the start address setting and the clock generation reference signal.

The present invention has been made in view of the above points, and an object of the present invention is to provide a sync signal separation device used for video signal processing that can obtain a restored signal with small jitter.

Means for Solving the Problems In order to solve the above problems, the present invention superimposes a sine wave burst signal on a level higher than the pedestal level between a horizontal sync signal lower than the pedestal level and a signal compressed on the time axis. A horizontal sync separation circuit that outputs only a horizontal sync signal and a delay circuit that delays the horizontal sync signal in order to obtain a sync signal that matches a predetermined edge of this sine wave burst signal during recording and reproduction. And a bandpass filter that outputs only a sine wave burst signal from the reproduction signal, and a waveform shaping circuit that makes the output a square wave,
The output of this waveform shaping circuit is used as the clock input, and the output of the delay circuit is used as the reset input.A shift register is provided, and the square wave obtained from the sine wave burst signal coincides with the edge of the shift register. The synchronization signal is obtained from the output of the shift register.

Effect The present invention, as described above, because the sine wave burst signal is at a higher level than the horizontal synchronizing signal, if the FM signal is modulated so that the horizontal synchronizing signal has a low frequency due to frequency deviation, Will occupy the higher
The demodulated sine wave burst signal has less carrier leak, and a higher signal-to-noise ratio can be obtained by passing it through a bandpass filter that allows the frequency of the sine wave burst signal to pass. It is possible to reduce the jitter of the restored signal by taking out the synchronizing signal that coincides with the above and using it for the start address setting of the memory and the clock generation reference. A method of extracting the sync signal that coincides with the predetermined edge of the sine wave burst signal will be described. With the above-described configuration of the present invention, a signal obtained by waveform-shaping a sine wave burst signal is used as a clock input of the shift register, and a horizontal synchronization signal delayed is used to reset the shift register immediately before the sine wave burst signal. As a result, a pulse corresponding to the edge of the wave of the sine wave burst signal at the stage number-th wave of the shift register is obtained at the output of the shift register.

Embodiment A sync signal separating apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of an embodiment of the present invention. In FIG. 1, 1 is a video signal a including a horizontal synchronizing signal and a sine wave burst signal.
, A horizontal sync separation circuit for outputting only the horizontal sync signal b, a delay circuit 2 for delaying the horizontal sync signal b, and a bandpass filter 3 for inputting the video signal a and passing the frequency of the sine wave burst signal ( BPF), 4 is a waveform shaping circuit that makes the output waveform of the output d of the bandpass filter 3 a square wave, and 5 is a shift that uses the output e of the waveform shaping circuit 4 as a clock input and the output c of the delay circuit 2 as a reset input. It is a register. The sync signal separation device configured as described above will be described.

FIG. 2 is a waveform diagram of a time-axis compression multiplexed video signal, and FIG. 3 is a waveform diagram of each part of FIG. FIG. 3a shows the sync signal and the sine wave burst signal of FIG. 2 in a time-enlarged manner. HS is a horizontal sync signal, PD is a pedestal level, CB is an achromatic level, and BS is a sine wave burst signal. is there.

In this figure, since it is a reproduced signal, it is assumed that the falling portion of the horizontal synchronizing signal HS has jitter due to carrier leak or the like (thick line portion).

The output of the sync separation circuit 1 is shown in FIG.
The delay circuit 2 shifts this to the front of the sinusoidal burst signal as shown in FIG. Further, the input video signal also passes through the band pass filter 3 and a sine wave burst signal is taken out as shown in FIG. This sine wave burst signal d becomes a waveform d'in the amplifier inside the waveform shaping circuit 4, and this signal is slice level Vth 2
A square wave e is obtained by digitizing, and this becomes a clock signal input to the shift register 5. The horizontal synchronizing signal at the front of the square wave e is always generated as is apparent from the relationship between the waveform d'and the set level Vth. Then, the output of the shift register 5 is reset by the output c of the delay circuit 2 as shown in FIG. 5F, and the waveform e obtained based on the sine wave burst signal is at the edge of the number of stages of the shift register 5. A synchronized sync signal is obtained.

The horizontal synchronizing signal b is shifted to the front of the sine wave burst signal by the delay circuit 2 in order to avoid an obstacle due to the horizontal synchronizing signal in the front part of the waveform e when the synchronizing signal f is obtained by the shift register 5. Is.

Since the rising edge of the synchronizing signal f shows an accurate phase regardless of the jitter of the horizontal synchronizing signal, if this is used as the reference signal, the jitter of the restored signal can be reduced.

As described above, the present invention provides a horizontal sync separation circuit that outputs only a horizontal sync signal, a delay circuit that delays the horizontal sync signal, and a bandpass filter that passes the frequency of a sine wave burst signal from a video signal. , A signal obtained by converting the output into a square wave through a waveform shaping circuit is used as a clock input, and the output of the delay circuit is used as a reset input to obtain a synchronization signal output that is not affected by jitter. If this is used as the reference signal, it is possible to reduce the jitter of the signal restored by expanding the time axis.

[Brief description of drawings]

FIG. 1 is a block diagram of a sync signal separating apparatus according to an embodiment of the present invention, FIG. 2 is a waveform diagram of an example of a time-axis compression multiplexed video signal, and FIG. 3 is a waveform diagram of each part of FIG. 1 ... Horizontal sync separation circuit, 2 ... Delay circuit, 3 ... Bandpass filter, 4 ... Waveform shaping circuit, 5 ... Shift register.

Claims (1)

[Claims] 1. A horizontal sync separation circuit which inputs a video signal including a horizontal sync signal and a sine wave burst signal and outputs only the horizontal sync signal, a delay circuit which delays the horizontal sync signal, and the video signal which is input. A bandpass filter that passes the frequency of the sine wave burst signal, and a waveform shaping circuit that makes the output waveform of the bandpass filter a square wave,
A synchronizing signal separation circuit, comprising: a shift register having an output of the waveform shaping circuit as a clock input and an output of the delay circuit as a reset input.