JPS6057275B2 - Video recording and playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color video recording and reproducing device, particularly a color killer (hereinafter simply referred to as "killer").

) Concerning improvements in signal generation circuits. Conventional color video recording and reproducing apparatus (hereinafter abbreviated as "VTR").

), a killer signal generation circuit using an automatic phase control system is configured during playback, but the automatic phase control system does not operate during recording, and the killer signal generation circuit is usually not configured. Even if a separate circuit was provided, it would still be an amplitude detection waveform. Therefore, there was a drawback that the killer circuit malfunctioned under noise or special electric fields.
This invention was made in view of these points, and it adds a switch circuit to the conventional circuit. During recording, the input signal to the phase detection circuit of the automatic phase control system is switched, and the automatic phase control system continues to operate. By doing so, the purpose is to obtain a phase detection waveform killer circuit with good performance even during recording.

FIG. 1 is a block diagram showing an embodiment of the present invention.
In the figure, 1 is a phase detection circuit of an automatic phase control (N°C) system, 2 is a crystal oscillator, and 3 is a signal that advances the signal phase of point a by 900 to which the output of crystal oscillator 2 is supplied and outputs it to point +
900 phase shift circuit, 4 is a burst signal input terminal, 5 is a variable frequency crystal oscillator, 6 is the output of the variable frequency crystal oscillator 5 +
A switch circuit that can connect the 900 phase shift circuit 3 to the point side,
7 is a drive input terminal of the switch circuit 6, 8 is an output terminal of the variable frequency crystal oscillator 5 to the sub-converter, 9 is a killer phase detection circuit, 1? is the killer signal output terminal to the killer amplifier.

In this embodiment, during reproduction, the crystal oscillator 2 is operating and the switch circuit 6 is in an OFF state.

Therefore, the output of the variable frequency crystal oscillator 5 is the output of the crystal oscillator 2 (phase φ1) and the reproduced burst signal (phase φ2), and the output of the APC phase detection circuit 1 is determined as φ1=φ2−90.
locked in position. On the other hand, the output of crystal oscillator 2 is +90
(b) After passing through the phase shift circuit 3, its phase becomes φ1+90+=φ2, and the killer phase detection circuit 9 detects the phase of the reproduced burst signal to obtain the desired killer signal output. Now, during recording, the crystal oscillator 2 is stopped and the switch circuit 6 is turned on (ON).

At this time, the output of the variable frequency crystal oscillator 5 is +90. Assuming that the signal phase that enters the terminal on the point b side of the phase shift circuit 3, passes through this transfer circuit 3 in the opposite direction, and exits on the point a side as φ1 as shown in the figure, M°C together with the received burst signal (phase φ2) The signal enters the phase detection circuit 1, and the output of the variable frequency crystal oscillator is locked to φ,=φ2-90 as before. Therefore, the output phase φ1+90 of the variable frequency crystal oscillator 6 becomes equal to φ2, and as in the case of reproduction, the phase is compared with the received burst signal in the killer phase detection circuit 9 to obtain the desired killer signal output. FIG. 2 is a circuit diagram in which +90 of this embodiment device embodies the phase shift circuit 3 and the switch circuit 6.
is composed of a coil L1 capacitors Cl, C2, and C3 and a resistor, and a switch circuit 6 is composed of a transistor Q1.
It consists of a diode D1, a resistor R3, and a capacitor C4, and the configurations of both are well known and do not require further explanation. This switch circuit 6 is turned on when a positive voltage is applied to the drive input terminal 7. As detailed above, in this invention, the A
Since the PC phase detection circuit and the killer phase detection circuit are operated also during recording to form a phase detection type killer circuit, a killer operation with good performance can be expected even during recording.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram embodying the main parts of the device of this embodiment. In the figure, 1 is an automatic phase control system phase detection circuit, 2 is a crystal oscillator, 3 is a +90 phase shift circuit, 4 is a burst signal input terminal, 5 is a variable frequency crystal oscillator, 6 is a switch circuit,
9 is a killer phase detection circuit.

Claims (1)

[Claims] 1 A crystal oscillator that oscillates at a predetermined frequency, the signal at the first terminal connected to the output of this crystal oscillator and the signal at the second terminal connected to the burst signal input terminal are compared in phase, and the phase difference is 90 degrees. An automatic phase control system phase detection circuit that controls the oscillation frequency and phase of a variable frequency crystal oscillator so that the signal phase at the second terminal is 90° from the signal phase at the first terminal to which the output of the crystal oscillator is connected. +90° phase shift circuit configured to advance, and this +90°
゜Equipped with a killer phase detection circuit that compares the phase of the signal from the second terminal of the phase shift circuit and the signal from the burst signal input terminal to generate a color killer signal, and stops the oscillation of the crystal oscillator during recording. At the same time, a switch circuit connecting the output terminal of the variable frequency crystal oscillator and the second terminal of the +90° transfer circuit is closed, and the output from the variable frequency crystal oscillator obtained through the switch circuit is transferred to the killer phase. A signal from the variable frequency crystal oscillator, which is supplied to the detection circuit and obtained at the first terminal of the +90° transfer circuit via the switch circuit, is supplied to the first terminal of the automatic phase control system phase detection circuit. A video recording and reproducing device characterized by: