JPS62108682A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To evade the occurrence of a buzz and the black sedated state of a picture in the specific reproduction state of a VTR by detecting the omission period of a video signal, and inserting another pulse from a pulse generator provided separately in the period. CONSTITUTION:The video signal and a horizontal synchronizing signal separated at a reproduction porocessing circuit 3 are supplied to a clamping circuit 24, and at the circuit, the sync chip of the video signal is clamped at a prescribed DC level. Also, the horizontal synchronizing signal is supplied to an AFC circuit 22 as a pulse generating means, and a pulse signal P synchronized with the horizontal synchronizing signal is outputted. Meanwhile, a detecting means 21 which detects the omission part of the video signal at the reproduction processing circuit 3 is provided, and a signal Sc which represents and omission from the detecting means 21 and the pulse signal P are given to an AND circuit 25. And when the omission part is recognized, a switching circuit 23 is switched by the output of the AND circuit 25, and a regulated DC voltage 26 set at the sync chip level is outputted.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is suitable for application to special reproduction of signals from a VTR (magnetic recording/reproduction device) such as slow reproduction or still reproduction on a monitor receiver. Related to signal processing circuits.
□ [Summary of the Invention] The present invention detects the missing period of the video signal in a special playback state such as slow or still playback of a VTR, and detects the K/'P pulse generation means within the missing period of the video signal.・By inserting a mother pulse signal), it is possible to avoid the generation of a buzz sound caused by the noise signal during this missing period, and also to avoid the phenomenon of darkening of the screen.

[Conventional technology]

For magnetic tapes where video signals are recorded diagonally with respect to the running direction of the magnetic tape, when playing video signals using a rotating magnetic head device, the running of the magnetic tape is stopped for still playback, and the running of the magnetic tape is stopped and In picture playback,
When the tape speed is set slower or faster than during metering, that is, in the above-mentioned special playback state, the magnetic tape is set at a speed different from that during recording.

And the male signal from the VTR mentioned above? For example, the tl or unmodulated playback signal that is modulated by a two-channel carrier wave signal and input from the antenna terminal of a television receiver (monitor receiver) is input to the video signal input terminal of the monitor receiver (of course, the audio signal is the audio signal). By supplying the signal directly to the input terminal of the monitor receiver, it is possible to view not only normal reproduced images but also special reproduced images such as sweeps and stills.

FIG. 3 shows an example of the connection relationship between a portion of such a VTR and a monitor receiver. To briefly explain this, (1) is the VTR, (2) is its rotating magnetic head, and (3) is the VTR.
) is a reproduction processing circuit for the video signal from the magnetic head, (4)
is an audio magnetic head, (5) is an audio signal processing circuit, (
6) and (7) are their output terminals. Further, (8) is a modulation circuit that modulates the above-mentioned signal into, for example, a two-channel television signal. (9) is its output terminal. In addition, mute switch α1 is installed in the audio signal output system.
During normal playback, the position is switched to the position shown by the solid line, and during other special playback, the position is switched to the position shown by the dotted line, so that the sound is not output to the outside.

α1) It is a Fi monitor receiver, where A is its antenna input terminal, and (to) is the A of the high frequency system connected to the next stage.
GC circuit, α→ is the demodulation circuit at the next stage, α is the input terminal of the video signal, αQ is the changeover switch that selects the video signal from this input terminal αυ or the video signal from demodulation circuit Q4, α is this The AGC circuit 0→ connected to the next stage of the switch αQ is a circuit for separating the luminance signal SY and the color signal Sc, and the luminance signal SY is supplied to the synchronization separation circuit (A) through the clamp circuit α field, and horizontal synchronization is performed. The signal S) I and the vertical synchronization signal Sv are obtained, and the horizontal synchronization signal SH is sent to the AGC circuit α.
It is planned that they will be returned to the country.

Then, the high frequency output terminal (9) of the vTRll) is connected to the antenna terminal α'4VC of the monitor receiver α, or the video output terminal (6) of the VTR (1) is connected to the monitor receiver α'4VC.
It is used by being connected to the video signal input terminal (b) of the

[Problems to be solved by the present invention]

In such a configuration, when special reproduction is performed in the above-mentioned VTR (1), the magnetic head (2) of the rotating magnetic head device scans diagonally across the recording trajectory of the video signal on the magnetic tape. If a guard band is provided between the recording trajectories, the magnetic head (2)
When crossing the video signal band, the video signal is missing and noise is generated, and the signal during the missing period of the video signal, that is, the noise signal, is:
The video signal is biased toward the white level side. This is for the amplification circuit of the signal reproduced by the rotating magnetic head, which has a reproduction characteristic that raises the white level side of the video signal relative to its black level side (sync chip side) in order to improve the image quality. This is because it is an endowment.

Such a video signal is transmitted to the modulation circuit (8)K of the VTR (1).
When the signal is supplied and modulated, the carrier level of the output becomes low in the noise portion, that is, the missing period of the video signal, as shown in FIG. 4AK. When such a modulated signal is input to the antenna of the monitor receiver, the high-frequency AGC circuit has a predetermined dyne during one video signal period, as shown in FIG. During the signal drop period T, an attempt is made to increase this low level signal so that it has a sufficiently high dyne. And this missing period T
Immediately after the process has finished, that is, in the blood M where the noise has disappeared, the high-frequency AGC circuit (to) is in full-dyne mode.At this time, when a modulated video signal is input to the high-frequency AGC circuit αIK, this video signal is The audio signal carrier itself becomes saturated during this full-dyne period, that is, the audio signal carrier is crushed, which causes a problem that a buzz sound is generated.

Furthermore, even if the video signal of the VTR (1) is directly input (without modulation) from the video input terminal α of the monitor receiver α and monitored, the following problems will occur. .

That is, in the AGC circuit α connected after the demodulation circuit α→ in the monitor receiver α, the peak AGC
As mentioned above, if the noise signal is biased toward the white level side of the video signal during the video signal dropout period T, there will be no black level component as a whole during this period, and this will cause The α power of the AGC circuit works in the direction of suppressing the white level component, which causes the problem that the entire screen becomes dark (the entire screen becomes dark).

In addition, due to the deviation of the noise signal towards the white level υ, the level of the sync chip within this period T also changes, and therefore the separation of the sync signal becomes uncertain, causing problems such as synchronization disturbances. The present invention solves these problems.

[Means for solving problems]

In the present invention, a detection means Q1 for detecting a missing period T of a video signal; ) is provided in the insertion means such as a switching circuit for inserting the pulse signal into the above-mentioned video signal dropout period T, and from this K, one pulse signal is inserted into the video signal dropout period T. .

[Effect]

Since this is K, a 9 pulse signal, which is the black level component of the video signal, is inserted within the missing period T of the video signal, so the AG
As a result, C times jI8 (1-13 or cl'i) are not operated in so-called full din even within this missing period T, and therefore are always operated in an appropriate r-in for t, so that the above-mentioned buzz is avoided. It is possible to avoid the occurrence of noise or darkening of the screen.

〔Example〕

An example of a video signal processing circuit according to the present invention will be described below with reference to FIG. 1. (2) and (3) are the above-mentioned rotating magnetic head and video signal reproduction processing circuit.

The video signal (including a luminance signal, a color signal, and a synchronization signal) separated in the reproduction processing circuit (3) is supplied to a clamp circuit (c), and the reproduction processing circuit (3)
The horizontal synchronizing signal sH separated therein is also supplied to this clamp circuit (c), where the above-mentioned sync chip f of the video signal is clamped to a required DC level.

The horizontal synchronizing signal SH mentioned above is supplied to the AFC circuit (AFC circuit), where a pulse signal P synchronized with the horizontal synchronizing signal SH from the reproduction processing circuit (3) is obtained. Due to the so-called flywheel effect of the AFC circuit (incorporated), this pulse signal P is
It is obtained with a period synchronized with the horizontal synchronization signal SH. Therefore, this AFC circuit) becomes the pulse signal generating means referred to in the present invention.

Furthermore, in the present invention, as described above, the video signal missing period T
A detection means Q]) is provided for detecting a dropout period in the video signal, but this is because VTRs are generally provided with a dropout compensation circuit, and this circuit also has means for detecting a dropout period in the video signal. However, when a dropout period is detected, interpolation is performed by inserting the signal of one horizontal period immediately before that period, so in the present invention, the dropout compensation circuit detects a dropout period of the video signal. detection means can be used.

However, in this case, since the dropout compensation circuit is generally provided to compensate for the IH, that is, the video signal during one horizontal period, the output from the detection means for the missing period of the video signal is also during the IH period. Therefore, in this example, a changeover switch (b) is provided, and in the solid line switching state of this changeover switch (b), the time constant of the means (c) is IH.
It is controlled so that it becomes several H in the dotted line state. This switch @ is switched to the solid line side in the normal playback state and to the dotted line side in the special playback state.

The signal Sc from the detecting means (c) for such a missing period T
and the above-mentioned pulse signal P from the AFC circuit (a) are supplied to the AND circuit (c) K, and when both signals become "1", the switching circuit (c) switches the side pressure shown by the dotted line.

This switching circuit (a) is the above-mentioned clamp circuit (
The output signal Sa of the output terminal (c) and the DC voltage of the DC voltage source (c) are switched and supplied to the output terminal (3a), and are normally in the switching position shown by the solid line. Further, the DC voltage of the DC power source (DC power supply) is selected based on the level of the sync chip of the video signal clamped by the clamp circuit (C).

According to this configuration, in the normal playback state, the magnetic head (2) of the rotating magnetic head device normally scans the video signal recording track on the magnetic tape, so that no signal is detected by the missing period detection means (c). Therefore, the switching circuit (in the switching circuit) remains in the state shown by the solid line, so that the output terminal (3a) K obtains a normal video signal power S. In this case, the switch (B) is in the solid line switching state.

Next, in the above-mentioned special reproduction state, the magnetic head crosses the guard band on the magnetic tape, and a video signal missing period 'i' 751 occurs. FIG. 2A shows the output signal S of the clamp circuit (c) in this case, and the period T
is the missing period mentioned above. And reproduction processing circuit (3)
The horizontal synchronizing signal SH obtained from the above is also missing after a missing period TKk as shown in Figure 2B, or this is the case in the A10 circuit)
, so from this A10 circuit (a),
As shown in Fig. 2 DK, it is synchronized with the 1 horizontal opening signal SIf,
Furthermore, a continuous 9 pulse signal P can be obtained.

On the other hand, as shown in FIG.
c is obtained. In the case of this special playback, the switch (C) is set to the dotted line switching shape 11, so the period of this signal Sc is several H, which is K so as to correspond to the missing period T.

Therefore, except for the missing period T of the video signal, the switching circuit (2) is at the solid line switching position, and within the missing period T, when the Noculus signal P is on, that is, "1", the output from the AND circuit (c) is Therefore, from this K, the switching circuit (in synchronization with this pulse signal P) is switched to the dotted line position. When switched to the dotted line position, the voltage of the DC power supply (c) is applied to the output terminal (3a) K, but this voltage is the same as the sync chip level of the video signal obtained from the clamp circuit (c). Therefore, according to the present invention, within the missing period T, the signal is synchronized with the )4 pulse signal P, that is, the horizontal synchronizing signal SH, and the level is the same as the sync chip of the video signal. /4
' will be inserted, and therefore the output terminal (3a
), a signal S8 shown in FIG. 2 EK is obtained.

By inserting the i44 pulse signal even within the missing period T of the video signal, the black level component is not mixed into the signal during this period, so as explained in FIG. 4A. As such, the carrier component does not decrease and the white level component does not become the only component, so the A on the monitor receiver side.
The GC circuit also operates almost normally, which solves problems such as buzzing noise and darkening of the screen.

In addition, the level of the pulse signal inserted within the missing period T is selected to be the same as the sync tip level of the Eirin signal obtained by the clamp circuit (c), and furthermore, this pulse signal is synchronized with the horizontal synchronizing signal SH. Therefore, synchronization disturbance can also be avoided.

〔Effect of the invention〕

According to the present invention described above, it is possible to avoid the generation of the above-mentioned buzz sound in the special playback state of a VTR, and also to avoid problems such as wiJWJ becoming black and synchronization disturbance occurring. It has the characteristics that can avoid

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing an example of a video signal processing circuit according to the present invention, Fig. 2 is a waveform diagram explaining its operation, Fig. 3 is a connection diagram between a conventional VTR and a monitor receiver, and Fig. 4 is a connection diagram showing an example of a video signal processing circuit according to the present invention. FIG. 3 is a waveform diagram illustrating this operation. (3) is a video signal reproduction processing circuit, (2) is a video signal reproduction processing circuit, and (2) is an A10 circuit. Figure 1 The output of the VTR's modified fox card (8) The output of the receiver's RF - AGC (r, 3) The output of the AGC (r, 3) Liquid form diagram 2

Claims (1)

[Claims] Detection means for detecting a missing period of the video signal when a magnetic tape on which the video signal is recorded diagonally with respect to the tape running direction is reproduced using a rotary head at a tape speed different from that during recording; An image comprising a pulse signal generating means for generating a pulse signal and a means for inserting the pulse signal, and the pulse signal is inserted into the missing period of the video signal by detecting the missing period. signal processing circuit.