JP3019313B2 - Synchronous signal automatic switching device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a television monitor,
The present invention relates to a synchronizing signal switching device required for displaying a high-definition television signal.

In general video equipment, a composite signal consisting of the same yellow signal and video signal is input, and the synchronization signal is separated from the composite signal inside the equipment.In the case of a video monitor, a completely independent synchronization signal is input from the outside. There are cases where it is adopted.

The present invention uses such a video monitor as a synchronization signal.
When an external synchronization signal is input, the synchronization signal is automatically switched from an internal signal to an external signal.

2. Description of the Related Art FIG. 3 shows a signal system diagram relating to synchronization signal switching in a conventional video monitor.

In FIG. 3, 9 is a current amplifying circuit for amplifying a composite signal including a synchronizing signal and a video signal, and 10 is a peak for fixing a positive peak at a constant DC level in the output of the current amplifying circuit 9. The clamp circuit 11, which is a voltage comparison, applies the output of the peak clamp circuit 10 to its comparison voltage input terminal, and installs its reference voltage input terminal. In this case, the internal synchronization signal is extracted from the composite signal by setting the reference value to zero level. On the other hand, when an external signal is to be used as a synchronization signal, the manual switch 12 is used to switch from the internal synchronization signal to the external synchronization signal.

FIG. 4 shows voltage waveforms at various parts of the conventional device. The operation of the conventional apparatus shown in FIG. 3 will be described with reference to FIG. Here, a high-definition television signal is set as an input signal.

4a is amplified by the current amplifier 9 and input to the peak clamp circuit 10. At this time, the output of the peak clamp circuit 10 is as shown in FIG. When this voltage is input to the voltage comparator 11 having a reference level of zero level, the output becomes an internal synchronization signal separated from the composite signal as shown in FIG. 4c.

Problems to be Solved by the Invention In the case of a conventional device, the selection of whether to use an internal signal separated from a composite signal or an external signal input from the outside of the device as a synchronization signal is performed by manually operating a switch. Therefore, there is a disadvantage that it takes much time and effort.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and enables automatic switching of a synchronization signal.

Means for Solving the Problems As a means for solving the conventional problems, the device of the present invention, when an external signal is input, sets a reference value of a voltage comparator to a constant high-level DC voltage value and has a large time constant. It has a vibrator, a voltage dividing resistor for adjusting the reference voltage to a desired value, and two monostable multivibrators having a relatively small time constant and a OR circuit in effect serving as an automatic switch for synchronizing signals. ing.

Operation With the configuration described above, the synchronization signal can be automatically switched from the internal synchronization signal to the external synchronization signal at the same time as the input of the external synchronization signal, so that the conventional switching operation can be omitted.

Embodiment FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows a voltage waveform of each part of the embodiment. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Here, as in the conventional technique, a high-definition television signal is set as an input signal.

In FIG. 1, 1 is a current amplifying circuit for amplifying a composite signal including a ternary synchronization signal, 2 is a peak clamp circuit for clamping a positive peak of the output of the current amplifying circuit 1, and 3 is a voltage comparator. Then, the output of the peak clamp circuit 2 is applied to the comparison voltage input terminal, and the reference voltage is applied to the reference voltage input terminal. In this case, a positive voltage is output when the comparison voltage is higher than the reference value.

On the other hand, when an external synchronizing signal is input to the device, a constant high-level DC voltage is output by the monostable multivibrator 5 having a time constant larger than the period. The high-level DC voltage value thus obtained is used as a reference value of the voltage comparator 3 after being finely adjusted by the resistance voltage divider 4. Here, the reference value of the voltage comparator 3 is a constant high-level DC voltage value, and since the voltage is constantly higher than the output waveform of the peak clamp circuit 2, the output becomes zero. By doing so, the process of separating the internal synchronization signal from the composite signal as performed by the conventional apparatus of FIG. 3 is suppressed.

The output of the voltage comparator 3 and the external synchronizing signal are each a monostable multivibrator 6 and 7 having a relatively small time constant.
To enter. Thereafter, the outputs of both are input to the OR circuit 8 to finally obtain a synchronization signal. Here, the circuit portion constituted by the two monostable multivibrators 6 and 7 and the OR circuit 8 substantially serves as a manual switch in the conventional device.

Next, the operation of each unit of the thus configured apparatus will be described with reference to FIG. 1 and FIG.

2a and 2b show the input waveform of the current amplifier 1 and the output waveform of the peak clamp circuit 2, respectively. here,
When the external synchronization signal shown in FIG. 2c is input from outside the device, the output waveform of the monostable multivibrator 5 having a large time constant becomes a high-level constant DC voltage V _CC as shown in FIG. The voltage is divided by the voltage divider 4 and becomes a reference value of the voltage comparator 3. However, since the output of the peak clamp circuit 2 is always smaller in amplitude than the above-mentioned reference value, the output of the voltage comparator 3 becomes zero, and the internal synchronizing signal is not reproduced from the composite signal.

Further, the output of the voltage comparator 3 and the above-mentioned external synchronizing signal are respectively connected to monostable multivibrators 6 and 7 having a relatively small time constant. The outputs of the monostable multivibrators 6 and 7 become f and g in FIG. 2, respectively, due to the characteristic of reacting when the input waveform rises. Then, the two outputs are input to the OR circuit 8 to finally obtain a synchronization signal as shown in FIG. 2h.

Effect of the Invention As described above, when an independent synchronization signal is input from the outside according to the present invention, the signal is automatically suppressed by the internal synchronization signal separated from the composite signal and signal processing, and the external synchronization signal is output with priority. Therefore, it is possible to save a great deal of trouble in conventional manual switch switching. Needless to say, the present apparatus can be used for general television signals.

[Brief description of the drawings]

FIG. 1 is a block diagram of an automatic synchronization signal switching device according to one embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation thereof, FIG. 3 is a block diagram of a conventional example, and FIG. FIG. 4 is a waveform diagram for explaining the operation. 2 ... peak clamp circuit, 3 ... voltage comparator, 4 ...
Divider, 5,6,7 …… Monostable multivibrator, 8 …… O
R circuit.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/04 H04N 5/08

Claims (1)

(57) [Claims] 1. A synchronizing signal is separated from a decoding signal including a synchronizing signal and a video signal to form an internal synchronizing signal. When an external synchronizing signal is input, the external synchronizing signal is output instead of the internal synchronizing signal. In the switching device, a current amplifier circuit for inputting the decoding signal, a peak clamp circuit for receiving an output of the current amplifier circuit, a voltage comparator for comparing an output of the peak clamp circuit with a reference voltage, A monostable multivibrator having the output of the comparator as an input, and having an external synchronizing signal as an input, having a time constant longer than the period of the external synchronizing signal, and having its output connected to the reference voltage of the voltage comparator through a resistor divider. A monostable multivibrator, a monostable multivibrator having the input of the external synchronization signal as input, and having a time constant shorter than a cycle of the external synchronization signal, and the voltage comparator An output of a monostable multivibrator having an output as an input and an output of a monostable multivibrator having a time constant shorter than the period of the external synchronization signal as an input, and an OR circuit having the output as a final output, Is applied, the reference voltage becomes higher than the output of the peak clamp circuit, the output of the comparator becomes zero, and a signal synchronized with an external synchronization signal instead of the synchronization signal of the decoding signal is output. An automatic synchronization signal switching device for outputting.