JPH02215289A - Composite video signal processing circuit - Google Patents

Abstract

PURPOSE:To always input a synchronizing signal to a following stage in any condition by switching the signal to the signal of a synchronizing signal generating circuit and supplying it to the following stage when a composite video signal is eliminated or in the case of a noise. CONSTITUTION:In a composite video signal processing circuit 10, the output of a synchronizing signal generating circuit 12 and a video signal A switched by an input switching circuit are switched by a changeover switch 13, an output signal B is obtained, and it is supplied to the following stage. For the signal to control the switch 13, the signal A is made into an input, and the control is executed by the output of a signal absence detecting circuit 11 to detect the signal absence. Namely, when the input signal does not exist, the switch 13 is switched at a (b) side, only the synchronizing signal is supplied from the circuit 12 to the following stage, and when the input signal exists, the signal is supplied to the following stage as it is in switching the switch 13 at an (a) side.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a composite video signal processing circuit for a television receiver or a video monitor, and more particularly to a circuit for synchronizing and stabilizing video when unattended.

Conventional technology Modern television receivers and video monitors are equipped with many external input terminals, and in actual use, signals are connected to all input terminals and signals are supplied to them. is rare. Furthermore, with recent advances in digital signal processing technology, memory has come to be actively used for processing video signals. Furthermore, an increasing number of TV receivers are equipped with on-screen functions that display channel numbers and input mode switching (e.g. video 1, video 2, etc.) on the screen, display sub-screens on the screen, and stay functions. ing. However, if there is a noise channel where the synchronization signal is unstable, or if the signal is unattended in video input mode, the synchronization signal may be lost, for example, the on-screen display position may become unstable and difficult to see.
Alternatively, the display position may have moved so much that it is no longer visible, causing discomfort to the viewer.

FIG. 4 shows the configuration of a conventional composite video signal processing circuit including an on-screen display section.

In FIG. 4, 1 is an input switching circuit, which connects the received television signal and the external input terminal video 1. Switch between video 2 and video 3 signals. This switched signal A is supplied to the video signal processing circuit 2 and the synchronization signal processing circuit 3. 4 is an on-screen generator, which generates horizontal PALNU H from the synchronization signal processing section.
P, the vertical pulse Vp is used as the reference for the display position. The on-screen output signal is sent to the video signal processing circuit 2 through R, G,
Added with B signal. 5 is a CRT.

Problems to be Solved by the Invention Here, the vertical pulse vP (vertical position) and horizontal pulse HP (horizontal position), which determine the on-screen display position, become unstable when unmanned or on a noise channel.

The present invention attempts to stabilize the synchronization signal even in a noise channel or no signal state, and also to stabilize the on-screen video signal.

Means for Solving the Problems The present invention includes a synchronization signal generator that generates a synchronization signal, a signal detection circuit that detects the presence or absence of a composite video signal, and switches between the output signal of the synchronization signal generator and the composite video signal. The switching circuit is configured to be controlled by the output of the signal detection circuit, and the output of the switching circuit is supplied to the subsequent stage.

According to the above-described configuration, the present invention determines that there is no signal in the noise channel or in the case of no signal, and supplies the output signal of the synchronizing signal generator to the subsequent stage by controlling the switching circuit, thereby detecting the signal. When the signal is correctly input to the circuit, it operates so as to supply the composite video signal as it is to the subsequent stage. In other words, the synchronization signal is always stably input to the subsequent stage in any state.

Embodiment Hereinafter, a composite video signal processing circuit according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall block diagram of a television receiver according to an embodiment of the present invention, FIG. 2 is a block diagram of a composite video signal processing circuit of the present invention, and FIG. 3 is a detailed block diagram of a no-signal detection circuit. and a waveform diagram.

In FIG. 1, a composite video signal processing circuit 10 of the present invention is connected after an input switching circuit 1, and its output is supplied to a conventional video signal processing circuit 2 and a synchronous signal processing circuit 3.

Next, a composite video signal processing circuit, which is a feature of the present invention, will be explained with reference to FIG. In FIG. 2, the television synchronization signal generation circuit 12 may use an IC that is already commercially available. The output of the synchronizing signal generation circuit 12 and the composite video signal A switched by the input switching circuit 1 are switched by a changeover switch 13 to obtain an output signal B, which is supplied to the subsequent stage. The signal for controlling this changeover switch 13 is the output of a no-signal detection circuit 11 which receives the composite video signal A and detects no-signal. In other words, when there is no input signal, selector switch 1
3 is set to the ■ side, only the synchronizing signal is sent from the synchronizing signal generator 12 to the subsequent stage, and when there is an input signal, the switch 13 is set to the ■ side and the synchronizing signal is directly supplied to the subsequent stage.

Next, a specific circuit of the no-signal detection circuit 11 will be explained with reference to FIG. The input signal A is synchronously separated by the synchronous separator circuit 14.■
get the signal. 9) Gar's mono multi 1
6 and obtain @ signal.

The changeover switch 13 is controlled by this signal.

Effects of the Invention As described above, according to the present invention, in the case of noise caused by the loss of a composite video signal, the signal is switched to the signal of the synchronization signal generation circuit and supplied to the subsequent stage, so synchronization is stabilized and on-screen display and memory Stable child screen display using . In addition, transients during input switching and channel switching are stable, and a stable image can always be provided.

[Brief explanation of the drawing]

FIG. 1 is an overall block diagram of a television receiver according to an embodiment of the present invention, FIG. 2 is a block diagram of a composite video signal processing circuit according to an embodiment of the present invention, and FIG. 3 is an example of a no-signal detection circuit. Embodiment Block Diagram and Waveform Diagram FIG. 4 is a block diagram of a conventional television receiver. 1...Input switching circuit, 2...Video signal processing circuit, lean generator, 6...CRT, 1o
...Composite video signal processing circuit, 11...
No signal detection circuit, 12... Television synchronization signal generation circuit, 13... Switching circuit, 14... Synchronization separation circuit, 15... Retrigger mono multi.

Claims (1)

[Claims] means for detecting the presence or absence of an input composite video signal, means for generating a synchronization signal, means for switching between the composite video signal and the synchronization signal, and switching of the switching means using a signal detecting the presence or absence of the composite video signal. A composite video signal processing circuit having control means.