JPH0450706Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a monitor television, such as a video monitor, which has a function of simultaneously displaying two or more types of video signals.

Conventional technology When switching video signals, conventional monitor televisions, etc. use a vertical synchronization signal as a trigger to provide a certain delay circuit, and while the delay circuit is operating, one video signal is displayed on the screen and the signal is switched. A method was used in which the other video signal was displayed after the end. Hereinafter, a conventional monitor television as described above will be explained using FIGS. 3 and 4.

A conventional monitor television is comprised of analog switches 1 and 2, a monostable circuit 3, a resistor R _O that determines the amount of delay, a capacitor C _O , and a video amplification circuit 4, as shown in FIG.

The specific operation will be explained below. A video signal is supplied to points A and B in FIG. 3, and a vertical synchronizing signal G is supplied to the monostable circuit 3. Monostable circuit 3, as shown in the timing chart in Figure 4, when vertical synchronization signal A is applied, capacitor C _O
The waveform of is as shown in (b), and the output waveform of the monostable circuit 3 is as shown in (c). Also analog switch 1,
When the control terminals a and b become high level, the switch 2 is closed and c, d and a, f are short-circuited, and when the control terminal becomes low level, c, d and e, f are opened.

Therefore, if the circuit configuration as shown in FIG.
d is short-circuited, and e and f of the analog switch 2 are opened, and the video signal supplied to point A is applied to the video amplification circuit 4.

Next, when the delay operation of the monostable circuit 3 ends,
Since the output becomes low level, analog switch 1 is opened and analog switch 2 is shorted, and the video signal supplied to point B is added to the video amplification circuit 4, and the image on the cathode ray tube surface is , the upper part shows the video signal supplied to point A, and the lower part shows the video signal supplied to point B. Note that V indicates the power supply voltage.

Problems to be Solved by the Invention However, in the conventional configuration, the delay amount of the monostable circuit is constant and the video signal is of an interlaced type, so the video signal supplied to point A and
The video signal supplied to point B cannot always be processed within the horizontal retrace period. For this reason, there was a problem in that noise was generated on the surface of the cathode ray tube at the time of signal switching.

In view of the above problems, the present invention provides a monitor television that can easily eliminate this switching noise.

Means for Solving the Problems In order to achieve the above object, the present invention provides a monostable circuit that determines the switching timing of a video signal, and a horizontal retrace pulse for an integral waveform signal that controls the delay amount of the monostable circuit. The configuration includes a horizontal retrace pulse generation circuit that superimposes the horizontal retrace pulse.

Effects With the above-described configuration, the present invention synchronizes the delay amount of the monostable circuit with the horizontal retrace pulse, so that the signal switching timing is performed within the horizontal retrace period, and switching noise is generated on the cathode ray tube surface. It is something that will stop happening.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a monitor television in an embodiment of the present invention, and FIG. 2 is a waveform diagram showing the same operation.

In Figure 1, A and B are video signals, 1 and 2 are analog switches, 3 is a monostable circuit, 4 is a video amplifier circuit, R _O is a resistor C _O is a capacitor, and V is a power supply voltage or higher. It is the same as the configuration. 5 is a horizontal retrace pulse generation circuit, and a resistor R ₁ and a capacitor C ₁ are used to superimpose a horizontal retrace pulse on the capacitor _CO .

The waveform of the horizontal retrace pulse is shown in A of Figure 2.
Due to this pulse, a pulsed charging current is supplied to the capacitor C _O through the resistor R ₁ and the capacitor C ₁ , so the voltage waveform of the capacitor C _O becomes the waveform shown in Figure 2 (b). . Therefore, the delay operation of the output of the monostable circuit 3 ends when the potential of the capacitor C reaches a certain level, but when this level is exceeded, it is always synchronized with the horizontal retrace pulse. The signal is shown in Figure 2C. Therefore, signal switching is performed within the horizontal retrace period.

Effects of the invention As described above, according to the invention, switching noise on the cathode ray tube surface due to switching of video signals can be easily removed, and the elements for signal switching are also required to be particularly high-speed. There is no need to use any elements, and the circuit can be constructed at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a monitor television according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing the same operation, FIG. 3 is a block diagram of a conventional monitor television, and FIG. 4 is a waveform diagram of the same. 1, 2... Analog switch, 3... Monostable circuit, 4... Video amplification circuit, 5... Horizontal retrace pulse generation circuit.

Claims (1)

[Scope of utility model registration request] It has means for displaying a plurality of video signals on a cathode ray tube in a time-divided manner, a monostable circuit that determines the switching timing of the video signals, and a monostable circuit that is horizontal to the integrated waveform signal that controls the amount of delay of the monostable circuit. A monitor television comprising: a horizontal retrace pulse generation circuit that superimposes a deflection retrace pulse, and switches the plurality of video signals within the horizontal retrace period.