JPH05268536A - Video signal mute circuit for television receiver - Google Patents

Abstract

PURPOSE:To improve a transient change of a white balance or the like and the lightness on a CRT screen due to the transient operation after the start of the operation of an automatic cut-off circuit after the end of video signal muting when a power switch is turned on. CONSTITUTION:As an input to a switching circuit 2 implementing muting of a video signal, a video signal mute pulse from a microcomputer 10 when a power switch is turned on and a masking pulse outputted from a video signal processing IC1 are ANDed and the resulting signal is used. An AND circuit 6 is used for ANDing and then an automatic cut-off control operation is attained even during mute period of a video signal and the consecutive transient operation even after the end of video muting is avoided.

Description

Detailed Description of the Invention

[0001]

The present description relates to a video signal mute circuit of a television receiver.

[0002]

2. Description of the Related Art In recent years, some high grade television receivers are equipped with an automatic cutoff circuit. The auto cutoff circuit will be briefly described.

An auto cut-off circuit means each R (red) / G (green) / B of a CRT (cathode ray tube or cathode ray tube).
(Blue) Changes in the light emission characteristics near the gun cut-off, temperature characteristics of the peripheral video circuit, and changes in the light emission characteristics due to the secular change The level is changed and the correction is performed.

2 and 3 schematically show the circuit configuration and control waveforms. As shown by the waveform 1 in FIG. 2, after the vertical blanking signal of the R / G / B video output signal, the R / G / B signals are time-divided in three horizontal periods, and the signals for the automatic cutoff control are provided. Has been inserted.

As shown in FIG. 3, the beam current I _B flowing through the CRT flows through the transistor 8 to the resistor 9 to generate a voltage corresponding to I _B × resistance value.

This voltage is input to the automatic cutoff control circuit via the switching circuit 7. The switching voltage waveform for controlling the switching circuit 7 is a waveform in which the vertical blanking signal period and the subsequent automatic cutoff control signal period are at a low level, as shown by the waveform 2 in FIG.

As a result, the signal voltage corresponding to the beam current is input to the automatic cutoff control circuit only during the vertical blanking signal period and the automatic cutoff control signal period, and the input signal level for the automatic cutoff control is input. However, the loop circuit is configured by operating so that the DC level of each R / G / B video signal output of the video signal processing IC 1 changes so that it is always constant.

Basically, this automatic cutoff circuit is CR
The purpose is to correct changes in characteristics of T over time, but like when the TV receiver power switch is turned on,
In principle, it also supports changes in CRT characteristics when the CRT heater or the like starts up from a sufficiently cooled state.

In this case, however, the CRT characteristic may be out of the control area of the automatic cutoff control circuit, or the correction may be overcorrected for a certain period due to the corresponding speed.

As a result, the screen brightness and white balance change when the power switch is turned on may be larger than in a conventional television receiver that does not have an automatic cutoff circuit.

Therefore, a video signal mute circuit when the power switch is turned on, which is generally composed of the microcomputer 9 and the switching circuit 2 in FIG. 3, is added.

[0012]

However, in the above circuit configuration, the video signal mute when the power switch is turned on is not yet sufficient.

After the power switch is turned on, by muting the image for a certain period of time, a large change in the brightness and white balance of the CRT screen due to characteristic changes until the heater or the like of the CRT is warmed is taken as a countermeasure.

However, in the video mute having the above circuit configuration, the signal for auto cutoff control is also muted, and the auto cutoff circuit is also turned off during the video signal mute period.

Therefore, at the same time when the CRT screen emits light after the end of the video signal mute, the automatic cutoff circuit also starts to operate at that time.

Therefore, depending on the operating speed of the auto cut-off circuit, the correction may be overcorrected for a certain period, or there may be some convergence period. This causes the CRT screen after the video mute ends. A large change in brightness or white balance may be detected.

In view of the above problems, the present invention provides a video signal mute circuit for a television receiver that improves a large change in the brightness and white balance of the CRT screen after the television receiver power switch is turned on.

[0018]

[Means for Solving the Problems] In order to solve the above problems,
The video signal mute circuit of the television receiver of the present invention is a pulse that includes within its period an auto cutoff control signal behind the vertical blanking signal of the television receiver and does not include the video signal portion within that period. And an AND (logical product) of a video signal mute pulse generated when the power switch of the television receiver is turned on.

[0019]

With the above-described structure, the present invention does not apply the video mute when the power switch is turned on to the signal for auto cutoff control after the vertical blanking signal, and the auto cutoff circuit starts to operate after the video signal mute ends. Instead, the auto cut-off circuit starts operating immediately after the power switch is turned on.

Therefore, due to the operating speed of the automatic cutoff circuit, the correction may be overcorrected for a certain period after the start of operation, or some convergence period may exist.
Large changes in brightness and white balance of the T screen are improved.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is an I for video signal processing.
C, 2 are switching circuits, 4 is a CRT cathode, 7 is a switching circuit, 8 is a transistor, and 9 is a resistor. The switching circuit 7, the transistor 8 and the resistor 9 constitute an automatic cutoff control input circuit. 6
Is an AND circuit, and 9 is a microcomputer.

The operation of the video signal mute circuit of the television receiver configured as above will be described below. In FIG. 1, R / G / B of IC 1 for video signal processing
The output is muted by using the switching circuit 2. The positive pulse for mute when the power switch is turned on is output from the microcomputer 9 and input to the switching circuit 2 via the AND circuit 6. The other input of the AND circuit 6 is connected to the masking pulse of the input signal to the automatic cutoff control circuit of waveform 2 in FIG. The content of this pulse is a pulse in which the vertical blanking signal and the signal period for the automatic cutoff control behind it are at the low level. As described above, the video signal mute of this circuit is applied only to the video signal portion excluding the vertical blanking signal and the signal period for the automatic cutoff control that follows. As a result, the automatic cutoff circuit starts operating immediately after the power switch is turned on.

As described above, according to this embodiment, the AND (logical product) of the video signal mute pulse when the power switch is turned on and the input signal masking pulse to the auto cutoff control circuit is used to obtain the video signal. After the mute ends, the auto cutoff circuit will not start operating. This can improve the phenomenon that a transient abnormal operation immediately after the start of the operation of the automatic cutoff circuit appears on the CRT screen.

[0025]

As described above, according to the video signal mute circuit of the television receiver of the present invention, the signal for the automatic cutoff control after the vertical blanking signal of the television receiver is within the period. After the mute of the video signal is completed, the AND (logical product) of the pulse including the video signal part which does not include within the period and the video signal mute pulse generated when the power switch of the television receiver is turned on is used. It is possible to prevent abnormal operation (overcorrection, having a convergence period of a certain time, etc.) immediately after the start of the operation of the automatic cutoff circuit.

Then, it is possible to improve the transitional large changes such as brightness and white balance appearing on the CRT screen.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a video signal mute circuit of a television receiver according to an embodiment of the present invention.

[Fig. 2] Waveform diagram of the signal for auto-cutoff control and waveform diagram of the masking pulse of the auto-cutoff control circuit input

FIG. 3 is a configuration diagram of a video signal mute circuit of a conventional television receiver.

[Explanation of symbols]

 1 IC for video signal processing 2 Switching circuit 6 AND circuit 7 Switching circuit 9 Microcomputer

Claims (1)

[Claims] 1. A pulse including a signal for automatic cutoff control after a vertical blanking signal of a television receiver within the period and not including a video signal portion within the period, and a power switch of the television receiver. AND with video signal mute pulse generated at ON
Video signal mute circuit of television receiver using (logical product)