JPH03206772A - Automatic changeover device for synchronizing signal - Google Patents

Abstract

PURPOSE:To save a trouble of switch changeover by suppressing an internal synchronizing signal separated from a composite signal automatically when an independent synchronizing signal is inputted externally and outputting the external synchronizing signal with priority. CONSTITUTION:A monostable multivibrator 4 having a large time constant which outputs a prescribed high level DC voltage in the input of the external synchronizing signal is provided and an analog switch 5 is thrown to the position of the external synchronizing signal by an output of the monostable multivibrator 4. Thus, as soon as the external synchronizing signal is inputted, the synchronizing signal is switched from the internal synchronizing signal into the external synchronizing signal automatically and a trouble of switch changeover having required in a conventional system is omitted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a synchronization signal switching device that is necessary when displaying a television signal or a high-definition television signal on a video monitor. Conventional technology In general video equipment, a composite signal consisting of a synchronization signal and a video signal is input, and the synchronization signal is separated from the composite signal inside the equipment, but in the case of a video monitor, a completely independent synchronization signal is input from the outside. There is a case to input and adopt it.

Figure 3 shows a signal system diagram used to switch synchronization signals on a conventional video monitor. In FIG. 3, 7 is a current amplification circuit that amplifies a composite signal including a synchronization signal and a video signal, and the negative peak of the output of this current amplification circuit 7 is fixed at a constant DC level by a peak clamp circuit 8. Ru. Reference numeral 9 denotes a voltage comparator which outputs an output when the output of the peak clamp circuit 8 is lower than a reference value. In this case, the internal synchronization signal is extracted from the composite signal by setting the reference value to the cello level. On the other hand, when it is desired to use an external signal as a synchronizing signal, the manual switch Y switch 10 is used to select and switch from the internal synchronizing signal to the external synchronizing signal. Figure 4 is a diagram of voltage waveforms at various parts of the conventional device.
With reference to FIG. 4, the operation of the conventional device shown in FIG. 3 will be explained. Here, a high-definition television signal is set as the input signal.

The composite signal in FIG. 4 fa) is amplified by the current amplification circuit 7,
It is input to the peak clamp circuit 8. At this time, the output of the peak clamp circuit 8 becomes as shown in FIG. 4(b). When this voltage is input to the voltage comparator 9 whose reference value is at zero level, its output becomes an internal synchronization signal separated from the composite signal as shown in FIG. 4(C).

Problems to be Solved by the Invention In the above-mentioned conventional device, the manual switch 10 is used to select whether to use an internal signal separated from the composite signal as a synchronization signal or an external signal input from outside the device. It has the disadvantage that it is extremely time-consuming.

SUMMARY OF THE INVENTION The present invention solves the above problems and aims to provide an automatic synchronization signal switching device that enables automatic switching of synchronization signals. Means for Solving the Problems In order to solve the conventional problems, the synchronization signal automatic switching device of the present invention is a monostable device with a large time constant that outputs a constant high-level DC voltage value when an external synchronization signal is input. A multivibrator is provided, and the output of the monostable multivibrator is used to switch the analog switch to the external synchronization signal side. Effect: With the above configuration, the synchronization signal can be automatically switched from the internal synchronization signal to the external synchronization signal at the same time as the external synchronization signal is input, thereby eliminating the trouble of conventional switch/gamma switch switching. EXAMPLE An example of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram of an automatic synchronizing signal switching device according to an example of the present invention, and FIG. 2 is a voltage waveform diagram of each part of the automatic switching device. Here, as in the conventional technique, a high-definition television signal is set as the input signal.

In Figure 1, 1 is 3! This is a t-current amplifier circuit that amplifies a composite signal including a synchronization signal, and the negative peak of the output of this current amplifier circuit 1 is fixed at a constant DC level in a peak clamp circuit 2.

3 is a voltage comparator that outputs a positive voltage when the output of the peak clamp circuit 2 is smaller than the reference voltage value, and the reference value is set to zero level. In this way, devices 1 to 3 have the same configuration as the conventional device.

On the other hand, when an external synchronization signal is input from outside the device, this external synchronization signal is input to the monostable multivibrator 4 having a time constant longer than the period of the external synchronization signal, and a constant high-level DC current is supplied from the monostable multivibrator 4. Voltage is output. The high level DC voltage value thus obtained is used as a control signal for the analog switch 5 connected to the voltage comparator 3. The analog switch 5 has two switching contacts 5a and 5b, one line in which the internal synchronizing signal output from the voltage comparator 3 is applied to the output terminal 7 via the switching contact 5a, and the other line in which the external synchronizing signal is applied to the switching contact 5b. The switching contact 5a is controlled by the output of the monostable multivibrator 4 which is inverted by the inverter 6, and the switching contact 5b is controlled by the output of the monostable multivibrator 4. It is configured to be directly controlled by. In this way, the output of the monostable multivibrator 5 and its inverted signal are respectively connected to the analog switch 5.
By inputting it as a control signal, it essentially functions as a manual switch in conventional equipment. Next, the operation of each part of the synchronizing signal automatic switching device configured as described above will be explained with reference to FIG. Second
Figures (a) to (C) show the input waveform of the current amplifier circuit 1, the output waveform of the peak clamp circuit 2, and the output waveform of the voltage comparator 3, which are the same as those of the conventional device. Here, when the external synchronization signal shown in Fig. 2 [d] is input from outside the device, the output waveform of the monostable multivibrator 4 with a large time constant will be a constant high level as shown in Fig. 2 [e]. This becomes the DC voltage Vcc and becomes a control signal for the analog switch 5. The output of the monostable multivibrator 4 and the inverted signal obtained by passing it through the inverter 6 cause the switching contact 5 to
By controlling b and 5a, switching contact 5b is turned on,
5a is set to OFFL, and finally an external synchronization signal as shown in Fig. 2ff) is obtained. On the other hand, if there is no external synchronization signal, the output of the monostable multivibrator 4 will be at a low level, the switching contact 5a will be turned on, the switching contact 5b will be turned off, and an internal synchronization signal will be obtained. Effects of the Invention As described above, according to the present invention, when an independent synchronization signal is input from the outside, the internal synchronization signal separated from the composite signal is automatically suppressed by signal processing, and the external synchronization signal is given priority. Since it can be output, it is possible to save a lot of effort compared to the conventional manual switching. Needless to say, this device can also be used for general television signals.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an automatic synchronous signal switching device according to an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of the automatic switching device, and FIG. 3 is a block diagram of a conventional synchronous signal switching device. 4 are waveform diagrams for explaining the operation of the conventional switching device. 1... Current amplification circuit, 2... Peak clamp circuit,
3... Voltage comparator, 4... Monostable multivibrator, 5... Analog switch, 6... Inverter.

Claims (1)

[Claims] 1. An analog switch that switches between the internal synchronization signal separated from the composite signal using a voltage comparator and the external synchronization signal input from outside the device, and an analog switch that has a time constant longer than the period of the external synchronization signal and A synchronous signal automatic switching device comprising a monostable multivibrator triggered by a signal, and configured to switch and control the analog switch using an output obtained from the monostable multivibrator.