JPS63142979A - Video muting circuit for tv tuner - Google Patents

Abstract

PURPOSE:To prevent an unbecoming picture from being generated at the time of switching a channel, by phase-synchronizing a receiver circuit with a synchronizing signal in video muting by muting a video signal part from which a synchronizing signal part is eliminated at the time of switching the channel. CONSTITUTION:An audio mute signal (b) is supplied to a switching circuit SW as a video mute signal via an AND gate G1. Thereby, an image is muted by setting a video signal to be outputted at, for example, a voltage E of pedestal level. At this time, by supplying burst pulses corresponding to a composite sync (horizontal and vertical synchronizing pulses) and a burst sections to the other input of the AND gate 1 via a NOR mate G2, the gate is closed, and in those sections, the switch SW is connected to a video signal side. Therefore, no image is displayed on a receiver 2 in a period of the video muting, however, a synchronous circuit, and a sub carrier circuit, etc., are synchronized with the synchronizing signal and the burst signal of an input.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video muting circuit for a TV tuner.

[Summary of the invention]

When switching channels, video muting is performed by setting the video output to a predetermined DC level for a predetermined period excluding the synchronization signal part, and during the mute period, the receiver circuit locks to the synchronization signal and synchronizes at the same time as muting is released. This is a video muting circuit that allows you to get a picture without any disturbance.

[Conventional technology]

A known TV receiver is one in which the cathode current is cut off when switching channels to prevent inter-office noise from occurring on the screen. Furthermore, when monitoring the reproduced signal of a VTR, etc., there is a system that mutes the audio signal of the receiver until a reproduced RF signal is obtained to prevent unpleasant noise from appearing (for example, 58-83440
(see publication).

[Problem that the invention seeks to solve]

T from the built-in TV tuner of the VTR or a standalone tuner.
When a TV broadcast reception signal is supplied to a V receiver, when a tuner selects a station, inter-station noise produces an unsightly screen and an unpleasant sound. In this case, it is difficult to control the cathode of the picture tube from the TV tuner side. Therefore, it is conceivable to mute the video signal and audio signal on the TV tuner side during channel selection. However, even if muting is canceled when the channel selection operation is completed, synchronization disturbances will occur on the screen until the receiver circuit (synchronous AFC) is synchronized with the input video signal, and subcarrier APC
It was inevitable that the locking would be delayed and color reproduction would be disrupted.

For this reason, in the past, only the audio signal was muted when switching channels, and no measures were taken to prevent image disturbance.

In view of this problem, it is an object of the present invention to prevent image disturbance from occurring when switching channels.

[Means for solving problems]

The video muting circuit for a TV tuner of the present invention includes:
A switch means SW is provided for selectively outputting a video signal and a predetermined DC signal.

When switching channels, the switch means outputs the DC signal for a predetermined period excluding a synchronizing signal portion.

[Effect]

The synchronization signal that continues to be supplied during the video mute period provides phase synchronization of the circuitry of the receiver.

An image without synchronization disturbance can be obtained at the same time as muting is released.

〔Example〕

FIG. 1 shows the main parts of a video muting circuit to which the present invention is applied. This circuit is provided at the video output section of the TV tuner 1 shown in FIG. When switching channels, an audio mute signal is generated with a predetermined time width in synchronization with the channel selection operation pulse a shown in FIG. Therefore, the audio signal delivered from the TV tuner 1 to the TV receiver 2 in FIG. 2 is muted during channel selection.

The audio mute signal is the AND gate G in Figure 1.
Switch circuit SW as a video mute signal via 1
supplied to As a result, the video signal to be outputted is set to a voltage level of, for example, the pedestal level, and the image is muted. At this time, composite sync (horizontal and vertical synchronization pulses) and a burst pulse corresponding to the burst period are applied to the other inputs of AND gate G1 via NOR gate G2 to close this gate, and in these periods, switch SW to the video signal side. Therefore, as shown in video output C in Fig. 3, the synchronization signal S Y
The NC and burst signal BU continue to be supplied to the TV receiver 2.

Therefore, during the video mute period, no image is displayed on the receiver 2, but the synchronous AFC circuit, subcarrier APC circuit, etc. are synchronized with the input synchronous signal and burst signal. Therefore, if video muting is canceled when the channel selection is finished, the image will be displayed immediately without synchronization disturbance or color blurring.

Note that the TV tuner 1 may be of an electronic type, and the image content is switched at a relatively early timing t1 immediately after the channel selection operation pulse (FIG. 3a) is generated. However, the synchronization phase and burst phase of the new station are completely different from the previous station, so
It is preferable to set the muting time so that the video mute and audio mute are performed until the TV receiver 2 is completely synchronized with the synchronization signal phase and the burst signal phase after tuning.

The muting level of the video signal may be any DC level that can be distinguished from the synchronizing signal, but is preferably a pedestal level.

FIG. 4 shows a specific example of the gate circuit shown in FIG.

The audio mute signal is applied to the base of the transistor Q2 through the resistor R1, and during the mute period, the transistor Q2 is turned on, and a low level video mute signal is obtained from the connection point between the collector of Q2 and the resistor R4. Composite shift and burst pulses are resistor R3
, R4 and added to the base of transistor Q1, turning on transistor Q1. Therefore, in the period of the synchronization signal and burst signal, the transistor Q
2 is turned off, the video mute signal returns to high level, and no muting occurs during these intervals.

〔Effect of the invention〕

According to the present invention, as described above (when switching channels, the video signal part except the synchronizing signal part is muted, so that the receiver circuit is phase-synchronized with the synchronizing signal during video miniaturization, and muting is performed. Immediately upon release, an image free from synchronization disturbances can be obtained.In other words, since no video is displayed until phase synchronization is achieved, an unsightly screen does not occur when switching channels.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a video muting circuit to which the present invention is applied, Fig. 2 is a connection diagram of a TV tuner and a TV receiver,
3 is a waveform diagram of each part of FIG. 1, and FIG. 4 is a circuit diagram of the gate circuit of FIG. 1. In addition, in the symbols used in the drawings, 1----------1---...-TV tuner 2-------------- V receiver SW - - - - - - Switch circuit G1 -
・・・〜・・・・−−−−1−−AND GATE G2−・・
-------1---- It is Noah Gate.

Claims (1)

[Claims] 1. A switch means is provided for selectively outputting a video signal and a predetermined DC signal, and when switching channels, the switch means outputs the DC signal for a predetermined period excluding a synchronizing signal portion. Video muting circuit for TV tuner. 2. The video muting circuit for a TV tuner according to claim 1, wherein the synchronization signal portion includes a color burst section.