JPS6350283A - Noise removal circuit - Google Patents

Abstract

PURPOSE:To remove noise entering a synchronizing separator circuit due to the omission of a signal by logically comparing an output from a variable delay circuit, which is obtained by delaying a horizontal synchronizing signal period TH, with a synchronizing signal. CONSTITUTION:An output signal from a synchronizing separator circuit 2 is logically compared with the output signal from the variable delay circuit 7, which is obtained by delaying the horizontal synchronizing period TH by about TH + DELTAt, and phase-compared with a reference horizontal synchronizing signal from an oscillator 4, thereby obtaining a phase comparison error signal. In such a way a horizontal synchronizing section including noise due to the omission of a signal is logically compared with a horizontal synchronizing section, which is delayed by about TH + DELTAt to exclude noise, thereby obtaining a noise- free horizontal synchronizing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a noise removal circuit for synchronizing signals included in video signals, and relates to a video disc.

”/TR and other video recording and reproducing devices.

Conventional technology In recording and reproducing video signals for video disks, VTRs, etc., a synchronizing signal is extracted from a reproduced video signal and delayed by falling or rising information of the synchronizing signal to obtain a burst gate signal. Alternatively, the phase of the horizontal synchronization signal is compared with all reference oscillation frequencies to obtain the time axis error signal 2, and all time axis correction control is performed. In a conventional video disc player, the circuit configuration for obtaining the time axis error signal is shown in Figure 3. show.

In FIG. 3, 1 is an input terminal for a video signal reproduced from a recording medium such as a video disk, 2 is a synchronization separation circuit that extracts a synchronization signal 2 from an input video signal, and 3 is a signal from an oscillator 4 that generates a reference oscillation frequency. a phase comparator for generating a phase error signal by comparing the phases of the signal and the synchronization signal;
is an output terminal that outputs a phase error signal.

Generally, in a video signal reproduced from a video disk or the like, a portion of the signal is dropped due to a defect in the recording medium, and the video signal jumps significantly to the white level or black level in the missing section. Such an example is shown in FIG. In FIG. 4, a is an input video signal, and b is a sync-separated output waveform when the input video signal is sync-separated at a voltage near the center of the sync signal, which has a negative polarity. As shown in a, the signal missing section jumps out below the black level or jumps out above the white level. When a noise component due to signal loss is extracted by the synchronization separation circuit, a large phase error is output when comparing the phases of the synchronization signal and the reference oscillation frequency, causing a malfunction in time axis correction.

Problems to be Solved by the Invention In the configuration of the conventional circuit described above, noise mixed into the synchronization separation output caused by signal dropout greatly impedes time base correction.

The present invention is intended to solve the problems related to the time axis correction and the like. In other words, noise mixed into the synchronization separation output caused by signal loss is removed, and stable time axis correction is provided.

Means for Solving the Problems In order to solve all of the above problems, the present invention changes the horizontal synchronizing signal period TII (TH=+83.5sa71sec) to Tli+
The device is characterized in that it is comprised of at least one variable delay circuit delayed by Δ, a logic multiplication circuit, a phase comparator, a low-pass filter circuit, and a voltage controlled oscillator.

Effect: With the above configuration, a synchronization signal containing noise caused by signal loss, etc. is logically compared with at least one variable delay circuit output signal obtained by delaying the horizontal synchronization signal period T3 synchronized with the synchronization signal by Tyo + Δ. By doing so, noise is removed, and since correct phase information of the synchronized i signal can be extracted, stable operations such as time axis correction control are possible.

Embodiment FIG. 1 is a block diagram showing a phase comparator circuit using an embodiment of the noise removal circuit of the present invention. In Figure 1,
1 is a video signal input terminal, 2 is a synchronization separation circuit that separates the synchronization signal from the input video signal, and 6 is a variable that delays the output signal (negative polarity) of the synchronization separation circuit 2 and the horizontal synchronization signal period T, QT yo + Δ. O logically compares the output signal of the delay circuit 7
R circuit, 3 is the reference oscillation frequency fB (fH=15.734
a phase comparator that generates a phase error signal by comparing the phases of the signal from the oscillator 4 that generates 264KH2) and the synchronization signal;
6 is an output terminal that outputs a phase error signal, 8 is a low-frequency r-wave circuit that waves the output of the phase comparator in a low frequency range, and 9 is a low-pass filter circuit 8
This is an oscillator that suffers from complete voltage control loss.

The output signal of the synchronization separation circuit and the horizontal synchronization signal period T, I are T
A logical comparison is made with the output signal of the variable delay circuit delayed by H+Δt, and the phase of this output signal is compared with the reference horizontal synchronization signal of the oscillator to obtain a phase comparison error signal. The phase comparison error signal is low-pass filtered, and the output of the low-frequency wave circuit is oscillated by voltage control.
The signal output from the variable delay circuit, which is delayed by Δ, is a signal synchronized with the reproduction synchronization signal.

FIG. 2 shows operational waveforms of each part of the present invention. In FIG. 2, a is a reference horizontal synchronizing signal, b is an input video signal, and the signal is missing in the video section. C is a sync-separated output when the input video signal is sync-separated at a voltage near the center of the sync signal. This synchronization signal output includes noise generated due to signal loss. d is the horizontal synchronization signal period TH'eT! ! This is the variable delay circuit output delayed by +Δ. e is an OR circuit output that logically compares the synchronization separation output C and the variable delay circuit output d delayed by Tyo + Δ, and is the output of a horizontal synchronization section containing noise due to signal loss and T
A horizontal synchronization period that does not include noise and is delayed by H+Δt is logically compared, and the period of the horizontal synchronization signal from which noise is removed is determined.

In the unlikely event that noise occurs at the same position in the horizontal synchronization interval delayed by T, noise will be included even after the logical comparison output, but this is extremely rare in practice.

Effects of the Invention According to the present invention, noise mixed into the output of the synchronization separation circuit due to signal loss etc. can be removed by logically comparing the output of the variable delay circuit with the horizontal synchronization signal period T□ and the synchronization signal. is possible. Furthermore 2xT11,
More stable noise removal is possible by adding a variable delay circuit, such as 3x'I'Yo.... As described above, the present invention is extremely useful in practice.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a noise removal circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing main part waveforms of the noise removal circuit of the present invention, and FIG. FIG. 4 is a block diagram showing the configuration, and a waveform diagram showing main part waveforms of a conventional phase comparator circuit. 1... Video signal input terminal, 2... Synchronization separation circuit, 3... Phase comparator, 4...
・Oscillator, 6... Phase error output terminal, 6...
...OR circuit, 7...Variable delay circuit, 8...
...Low frequency r-wave circuit, 9...Voltage controlled oscillator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (Figure 3 Figure 4)

Claims (1)

[Claims] The period T_H of the reproduction synchronization signal separated from the video signal reproduced from the recording medium and the reference horizontal synchronization signal is T_H+
at least one variable delay circuit that delays by Δt; a circuit that logically multiplies the reproduction synchronization signal and the output of the variable delay circuit; and a phase comparator that compares the phases of the output of the logical multiplication circuit and the output of the reference horizontal synchronization signal of the oscillator. and a low-pass filter circuit that low-pass filters the phase comparison output, and an oscillator that performs voltage-controlled oscillation using the output of the low-pass filter circuit, and inputs the output of the voltage-controlled oscillator to the variable delay circuit and generates the reproduction synchronization signal. A noise removal circuit characterized in that noise contained in a reproduced synchronization signal after synchronization separation is removed by logically multiplying the output of the variable delay circuit.