JPS6235787A - Noise eliminating circuit - Google Patents

Abstract

PURPOSE:To extract only phase information on a synchronizing signal by remov ing noises which do not synchronize with the synchronizing signal by a monostable multivibrator which pulses shorter than the synchronizing signal and generate pulses having pulse with a little bit shorter than horizontal synchro nizing periods. CONSTITUTION:A pulse width selecting circuit 6 removes noises which have pulse width shorter than the synchronizing signal from a synchronous signal separation output. For example, the selecting operation is performed on the basis of pulse width of about 4.5musec shorter than the pulse width of the synchro nizing signal. The monostable multivibrator 7 being to pulse from the waveform leading or trailing edge information on the synchronizing signal from which short impulsive noises are removed to generate pulses with pulse width a little bit shorter than the horizontal synchronizing periods TH. At this time, when the selection pulse width of the pulse width selecting circuit 6 is set to T1(musec), the pulse width T2(musec) of the monostable multivibrator 7 is so set that TH> T2>=TH-T1, thereby removing noise components completely.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention removes noise from synchronization signals contained in video signals, and is mainly used for noise removal in video recording and reproducing devices such as video tape recorders and video discs. It is related to circuits.

Conventional technology When recording and reproducing video signals in video tape recorders, video disk players, etc., a synchronization signal is extracted from the reproduced video signal, and a burst gate signal is obtained with a delay from the rising or falling information of the synchronization signal, or a horizontal synchronization signal A time axis correction signal is obtained by comparing the phase with the reference oscillation frequency. Figure 3 shows a phase comparator circuit that compares the phase of a synchronization signal and a reference oscillation frequency, which are used for time axis correction in a conventional video disc player. 2 is a sync separation circuit that extracts a sync signal from the input video signal; 3 is a sync separation circuit that compares the phase of the sync signal with a signal from an oscillator 4 that generates a reference excavation frequency to generate a phase error signal. Phase comparator, 5
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 lost 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) shows the input video signal, and (b) shows the sync-separated output waveform when the input video signal is sync-separated at a voltage near the center of the sync signal.

As shown by (-), the signal missing section jumps out below the black level or jumps out above the white level.

If noise components due to signal loss are also extracted by the synchronization separation circuit 2, a large phase error will be output in the phase comparison with the reference oscillation frequency, and the time axis correction will malfunction.

Problems to be Solved by the Invention However, in such conventional circuits, noise mixed into the synchronization separation output caused by signal loss poses a major obstacle to time base correction, etc.

The present invention has been made in view of the above points, and an object of the present invention is to provide a noise removal circuit that uses a simple configuration to remove noise mixed into the synchronization separation output caused by signal dropout or the like.

Means for Solving the Problems In order to solve the above problems, the present invention eliminates pulses shorter than the synchronization signal by using a pulse width selection circuit that selectively removes pulses shorter than the horizontal synchronization signal, and also removes pulses shorter than the horizontal synchronization signal. A device that correctly extracts only the phase information of the synchronization signal by removing noise that does not match the synchronization of the synchronization signal by using a monomulti that generates a pulse with a pulse width slightly shorter than TH (TH = e 3.sss, xsec). It is.

With the above-described configuration, the present invention can eliminate noise that enters the synchronization separation circuit caused by signal loss, etc., and extract correct phase information of the synchronization signal. Therefore, the phase of the synchronization signal is compared with the reference oscillation frequency. The burst gate circuit that generates the burst gate signal with a delay from the time axis control and synchronization signal will not malfunction.

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 FIG. A sync separation circuit 6 is a pulse width selection circuit that removes noise having a pulse width shorter than the sync signal from the sync signal separation output. For example, in 07, which is selected when the pulse width is around 4.5μ which is shorter than the synchronization signal pulse width, the pulse is started from the waveform rising or waveform falling information of the synchronization signal from which short pulse-like noise has been removed, and the horizontal synchronization period TH This is a monomulti that generates a pulse with a slightly shorter pulse width. At this time, if the selection pulse width of the pulse width selection circuit 60 is T1 (7 IScc), the pulse width T2 (/lsa::) of the monomulti 7 is TH>T2≧TH−T.

The noise component is completely removed. Furthermore, the horizontal synchronization signal from which noise due to signal loss etc. has been removed by the monomulti 7 is the reference oscillation frequency fH of the reference oscillator 4 (fH = 15.734264kHz)
The phases are compared by the phase comparator 3, and a phase error signal is extracted and output from the output terminal 5.

FIG. 2 shows operational waveforms of each part of the present invention. In FIG. 2, (-) is an input video signal, which has noise due to wide signal dropouts and noise due to narrow signal dropouts in the video signal section. (b) shows the synchronous separation output when the input signal is synchronously separated at a voltage near the center of the synchronous signal. This synchronization separation output includes wide pulses and narrow pulses due to signal loss. (C) is the output of the pulse width separation circuit, in which pulses narrower than the synchronizing signal are removed, leaving only the wide pulses due to signal loss. (d) is a monomulti output, and since the monomultiple becomes insensitive by a pulse width slightly shorter than the horizontal synchronization period from the falling edge of the synchronization signal, only the signal having the same period as the horizontal synchronization signal is extracted. In other words, only the horizontal synchronization signal information can be extracted accurately.

Effects of the Invention As described above, according to the present invention, with an extremely simple circuit configuration, it is possible to stably remove noise that mixes into the output of the synchronization separation circuit due to signal loss, etc., and is extremely useful in practice.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a phase comparison circuit using a noise removal circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram of main parts of the noise removal circuit of the invention, and FIG. 3 is a conventional phase comparison circuit. FIG. 4 is a block diagram illustrating a waveform diagram of a main part of a conventional phase comparator circuit. 1... Video signal input terminal, 3... Phase comparator, 4... Excavator, 5... Phase error output terminal, 6... Pulse width selection circuit. , 7...Mono multi. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure No. 2121 cd-)

Claims (1)

[Claims] a pulse width selection circuit that selects and removes pulse widths shorter than the synchronization pulse width from a synchronization signal separated from a video signal reproduced from a recording medium; a noise removal circuit for removing unnecessary pulse noise of the synchronization signal separated from the video signal; .