JPS631500Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a so-called video switch circuit that supplies or cuts off a video signal to be supplied to video equipment on the supplied side, or switches to another video signal.

There are many cases where it is desired to cut off the video signal in a circuit that supplies the video signal to a video device on the supplied side. In this case, if you simply cut off the video signal and do not supply any signal, it will cause a synchronization disorder in the video equipment on the supplied side, so the video equipment on the supplied side will no longer be synchronized, and then the video switch circuit When the device is turned on and the supply of video signals is restarted, a problem arises in that synchronization is disrupted for a while. In order to prevent such problems, it is necessary to apply only the synchronization signal included in the video signal to the supplied video equipment when the video signal is cut off in the off state. Therefore, the video switch circuit is configured to switch the video signal to a synchronization signal when the video signal is normally cut off. However, it goes without saying that such a video switch circuit must output a synchronization signal that has the same waveform as the synchronization signal included in the video signal that was being output until switching, and each part of that waveform must be The disadvantage is that the configuration is complicated because it is necessary to match the potentials of the two.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a video switch circuit with a simple configuration that can supply and cut off video signals to video equipment on the supplied side without causing synchronization disturbances.

The video switch circuit according to the present invention corresponds to the output of a first clamp circuit that clamps a first predetermined portion of a video signal waveform to a predetermined clamp potential, and corresponds to the first predetermined portion of a synchronization signal waveform separated and extracted from the video signal. It is configured to selectively output one of the output of a second clamp circuit that clamps the second predetermined portion to the predetermined clamp potential and a predetermined potential having a predetermined difference from the predetermined clamp potential.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, a predetermined clamp potential V _A is applied from a first voltage source 1 to first and second clamp circuits 2 and 3.
is supplied to. A video signal A is supplied to each of the clamp circuit 2 and the sync separation circuit 4 via an input terminal IN. In the clamp circuit 2, the pedestal level of the video signal A or the potential at the lowest potential portion of the synchronization signal included in the video signal A (hereinafter referred to as the sync chip level).
is clamped to the clamp potential V _A. In the synchronization separation circuit 4, the synchronization signal is separated and extracted from the video signal A. The separated and extracted synchronization signal is supplied to a clamp circuit 3, where the potential at the highest potential portion of the synchronization signal or the sync chip level is clamped to the clamp potential _VA . A second voltage source 5 that generates a voltage V _B is connected to the output end of the voltage source 1 that generates the clamp potential V _A , and the potential at the output end of the voltage source 5 becomes a predetermined potential V _A +V _B. The predetermined potential V _A +V _B , the output B of the clamp circuit 2 and the output C of the clamp circuit 3 are each supplied to the switch means 6 .

In the switch means 6, a predetermined potential V _A +V _B ,
Each of the outputs C is supplied to each of the X side contact and the Y side contact of the video switch element _SW1 as the first switch element. The movable contact of switch element SW ₁ is the second
It is connected to the Y side contact of the video switch _SW2 as a switch element. The output B is supplied to the X-side contact of the switch element SW ₂ , and the movable contact of the switch element SW ₂ is connected to the output terminal OUT. still,
In each of the switch elements SW ₁ and SW ₂ , when each of the binary signals D and E applied to each of the control input terminals CONT ₁ and CONT ₂ is at a high level, the movable contact of each of them comes into contact with the contact on the X side. However, when each of the signals D and E is at a low level, the movable contact contacts the Y-side contact. The synchronization separation circuit 4 also determines that the amplitude of the separated and extracted synchronization signal, which is the output thereof, is determined by the amplitude of the synchronization signal included in the video signal A, that is, the potential difference V _C between the pedestal level and the sync chip level in the video signal A. are constructed to be equal.

The operation of the above configuration will be explained using FIG. 2. When the sink chip level is clamped to the clamp potential V _A in clamp circuits 2 and 3, the input terminal IN is
When a positive video signal in which the pedestal level and the sync chip level fluctuate as shown in _FIG . At this point, the pedestal level is the potential
It becomes V _A + V _C. At the same time, a synchronously separated synchronous signal is supplied from the synchronous separator 4 to the clamp circuit 3, and the output C of the clamp circuit 3 is a synchronous signal whose sync chip level is clamped to the clamp potential V _A as shown in FIG. 2c. Become. Output C at this time
The potential at the low potential portion of is the clamp potential V _A , and the potential at the high potential portion is higher than the clamp potential V _A by a potential difference V _C corresponding to the amplitude of the synchronization signal.

Now, voltage V _B of voltage source 5 is applied to clamp circuits 2 and 3.
When a high potential signal and a low potential signal are applied to each of the input terminals CONT ₁ and CONT ₂ after adjusting the potential difference to be equal to the potential difference V _C corresponding to the actual amplitude of the synchronization signal output from the switch element. SW ₁
The movable contact in switch element SW2 contacts the contact on the X side, and the movable contact in switch element _SW2 contacts the contact on the Y side. As a result, the signal F supplied to the output terminal OUT becomes a constant level signal equal to the potential V _A +V _C at the pedestal level of the signal B output from the clamp circuit 2. This operation turns off the video switch circuit so that unstable video signals and synchronization signals are not supplied to the supplied video equipment during the period from when the supplying video equipment is turned on until it reaches a steady state. This is done when the video equipment on the supply side is in a steady state and outputs stable video signals and synchronization signals, thereby preventing more level fluctuations than necessary (section f in FIG. 2).

Next, when a low potential signal is applied to each of the input terminals CONT ₁ and CONT ₂ , the switch elements SW ₁ and SW ₂
The movable contacts in each contact the Y-side contacts. As a result, the signal F at the output terminal OUT becomes only the same signal as the output C of the clamp circuit 3, that is, a synchronous signal (section f in FIG. 2).

Furthermore, when a high potential signal is applied to the input terminal CONT ₂ , the movable contact in switch element SW ₂ contacts the contact on the X side, and regardless of the state of switch element SW ₁ , the sink chip level of signal F becomes the clamp voltage.
It is the same signal as the video signal clamped to V _A , that is, the output B of the clamp circuit 2 (Fig. 2 f
Section Q).

The above is the clamping potential of the sync chip level.
Although this is the operation when the pedestal level is clamped to the clamp potential V _A , _{the same operation can be obtained by adjusting the voltage V B of} the voltage source 5 to be zero. However, in this case, the sync chip level of each of the signals B, C, and F becomes V _A - V _C. In addition, the DC potential output in section P in Figure 2 f does not necessarily have to be the pedestal potential, but can be set to any optimal potential that meets the requirements of the supply side and the supplied side. The voltage V _B of the source 5 may be adjusted.

As detailed above, the video switch circuit according to the present invention has a simple structure consisting of two clamp circuits, two video switch elements, two voltage sources, and one synchronous separation circuit. Furthermore, since the video switch circuit according to the present invention has a configuration in which the output of the sync separation circuit 4 is not directly output but is output via the clamp circuit 3, the potential of the voltage source 5 is actually output from the clamp circuits 2 and 3. Since the amplitude is set equal to the amplitude of the synchronization signal, the pedestal level and sync chip level of the signal F supplied to the output terminal OUT are stable when the switch is switched, and the synchronization of the video equipment on the supplied side is not disturbed. do not have. Furthermore, since the video switch circuit according to the present invention has a configuration that can be easily integrated into the same integrated circuit, by integrating it, it is possible to uniformly suppress variations in each element and fluctuations due to temperature, etc., and output signals. can be made stable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a waveform diagram showing the operation in FIG. 1. Explanation of symbols of main parts, 1, 5... Voltage source,
2, 3... Clamp circuit, 4... Synchronous separation circuit,
_SW1 , _SW2 ...Video switch elements.

Claims (1)

[Claims for Utility Model Registration] (1) A first clamp circuit that clamps the potential at a first predetermined portion of the video signal to a predetermined clamp potential, and a synchronization separation circuit that separates and extracts a synchronization signal included in the video signal; a second clamp circuit that clamps a potential at a second predetermined portion corresponding to the first predetermined portion in the separated and extracted synchronization signal to the predetermined clamp potential; a first voltage source that supplies a potential; a second voltage source that generates a predetermined potential having a predetermined difference from the predetermined clamp potential; and any one of the outputs of the first and second clamp circuits and the predetermined potential. and switch means for selectively supplying video to an output terminal. (2) The switch means includes a first switch element that selectively outputs either the predetermined potential or the output of the second clamp circuit, and an output of the first switch element and the output of the first clamp circuit. 2. The video switch circuit according to claim 1, further comprising a second switch element that selectively supplies one of the outputs to the output terminal.