JPS63283281A - Video output device - Google Patents

Abstract

PURPOSE:To output a video signal resistant to external noise even in a case where no signal exists on a master picture and the cycle of whose synchronizing signal coincides with the cycle of an ordinary television signal, by using the synchronizing signal of a slave picture side by detecting the fact of the no signal of the master picture when it occurs, in the case that the slave picture is inserted in the master picture. CONSTITUTION:From inputted master picture and slave picture, the synchronizing signals are extracted by synchronization separating circuits 12 and 15, and are inputted to a synchronizing signal switching circuit 14. The synchronizing signal switching circuit 14 switches the synchronizing signal to that of the slave picture only when no signal exists on the master picture by a master picture no signal detection circuit 13. A signal made into the slave picture by a slave picture conversion circuit 16 is synthesized with the master picture generally at a picture synthesizing circuit 11, and when no signal exists on the master picture, only a slave picture forming signal is outputted. Next, a synchronizing signal detector 21 detects the synchronizing signal from the master picture. The signal is stored in a capacitor, and increases the base potential of a transistor 22, and turns ON the transistor. As a matter of course, the transistor is burned OFF at the time of no signal on the master picture. By turning OFF the transistor, a vertical synchronizing signal VD is switched from a master VD to a slave VD by a synchronizing signal change-over switch 23.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a video output device, and sometimes to an optimal device for two-plane image compositing.

[Conventional technology]

In recent years, the introduction of digital technology into home appliances such as television receivers and videotape recorders has increased significantly.

As an example of this, a device has appeared that employs a method of inserting a child screen in which another screen is reduced by a certain area ratio into a main screen (hereinafter referred to as P in P).

Let us consider a case in which the main screen outputs a child screen when there is no signal in this PinP circuit.

Generally, a period separation circuit for a main screen that controls the entire PinPl path requires a circuit that generates a synchronizing signal even when there is no signal.

If this circuit has an analog circuit configuration, that is, if it has a self-oscillation circuit and synchronizes both the frequency and phase shift when a synchronizing signal is input from the outside, the noise will cause noise when there is not a completely no signal. This is a problem because it causes stable operation.

In addition, if this circuit has a digital circuit configuration, that is, if it uses a method that counts down the clock, the circuit generally makes the vertical period longer than the actual period in order to take synchronization in when there is no signal. Because it is set to , synchronization may not be possible depending on the TV receiver.

Related devices of this type include, for example, Japanese Patent Application Laid-Open No. 6
1-194984 and the like.

[Problem that the invention seeks to solve]

As described above, when using the above conventional technology to output a sub screen when the main screen has no signal, the method using an analog synchronization separation circuit has the problem of being weak against external S noise. Even when a typical sync separation circuit is used, the vertical synchronization period becomes wide (and depending on the TV receiver, the entire period (
There was a problem with synchronization.

An object of the present invention is to provide a device that is resistant to external S noise (and synchronized even with television receivers all over the world) when outputting a sub-screen when there is no signal on the main screen.

[Means for solving problems]

The above objective can be achieved by detecting when there is no signal on the main screen and using the synchronization signal on the sub-screen side.

[Effect]

Detects when the main screen becomes silent and [by using the synchronization signal on the child screen side, the child screen! Only the Ii plane signal is output.

〔Example〕

FIG. 1 shows an overview of the present invention.

The input main screen and child screen are synchronized by the synchronous separation circuits 12 and 15.
Extract the synchronization signal by The extracted synchronization signal is input to the synchronization signal switching circuit 14. The synchronization switching circuit 14 uses the main screen no-signal detection circuit 13 to switch to the sub-screen synchronization signal only when there is no signal on the main screen. The signal converted into a small screen by the small screen conversion circuit 16 is normally combined with the main screen in the screen synthesis circuit 11, but when the main screen has no signal, only the small screen signal is output.

Next, an embodiment of the present invention will be explained with reference to FIG. 2.

First, the synchronization signal detector 21 detects a synchronization signal from the main screen. This signal is applied to the capacitor, raising the base potential of the transistor 22 and turning the transistor on. Naturally, when there is no signal, the transistor is off. By turning off this transistor, a vertical synchronizing signal (hereinafter referred to as Vf) is generated.
2), the synchronization signal changeover switch 23 switches from the parent VD to the child VD.

〔Effect of the invention〕

According to the present invention, by adding a very simple circuit, it is possible to output a video signal that is resistant to external noise even when there is no signal on the main screen (and whose synchronization signal period matches the period of a normal TV signal). .

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the present invention, and FIG. 2 is a diagram showing an embodiment of the present invention. 11... Screen composition circuit, 12... Synchronization separation circuit, 1
5...R screen no signal detection circuit, 14...Synchronization signal switching circuit, 15.-Synchronization separation circuit,
16...Small screen conversion circuit, 21...Sync signal detector, 23...Sync signal changeover switch. Figure 1 High Figure 2

Claims (1)

[Claims] 1. In a device that synthesizes a video signal reduced to the required size with a normal video signal, a period separation circuit for two signals, a no-signal detection circuit that detects when there is no signal of the normal video signal, and a signal that combines the signal when there is no signal. A video output device comprising a synchronization signal switching circuit that switches control of the circuit from a synchronization signal of a normal video signal to a synchronization signal of a reduced video signal.