JPH0434616Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a video signal switching circuit, and particularly to a video signal switching circuit for a television signal transmission device.

[Conventional technology]

Conventionally, this type of video signal switching circuit has a plurality of first switching devices 2, a plurality of second switching devices 3, and a control circuit that switches at the leading edge of a switching clock pulse, as shown in FIG.

[Problem that the invention attempts to solve]

The conventional video signal switching circuit described above has a plurality of first and second switching devices, and switches at the leading edge of the switching clock pulse, so this problem occurs when switching the cross point of the first switching device. The disadvantage is that the switching noise and the switching noise generated when switching the cross point of the second switch overlap, resulting in an increase in the absolute value level of the switching noise that appears at the output of the video signal switching circuit. .

[Means for solving problems]

The video signal switching circuit of the present invention includes a plurality of first switching devices each including a plurality of cross points, a second switching device whose input terminal receives the outputs of the plurality of first switching devices, The first switch has a control circuit that switches on the leading edge of the switching clock pulse, and the second switch has a control circuit that switches on the trailing edge of the switching clock pulse.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a system diagram of an embodiment of the present invention. 1
2 is a video signal switching circuit, 2 is a first switch, 3 is a second switch, 4 is a control circuit, 5 is an inverter in the control circuit, and 6 is an output terminal.

If the output terminal of each cross point is an emitter output as shown in FIG. 3, a constant current load, a resistive load, etc. are required. The timing when switching the crosspoint in the first switch is as shown in FIG. 4 when switching from crosspoint A to crosspoint B. When switching, the two crosspoints momentarily turn on, and 1/2 current flows to the output terminals of the two crosspoints. 1/2 current flows through cross point A, which should be OFF.
This is the cause of switching noise, but if the timing is set such that the two crosspoints are in the OFF state at the time of switching, as shown in Figure 5, no crosspoints will be taken at any moment, which poses a practical problem. Therefore, if the output resistance of the cross point A is R (including the emitter resistance of the transistor), switching noise of 1/2R occurs. A similar phenomenon occurs when the cross point of the second switch 3 in FIG. 1 is switched.

Therefore, when switching from cross point A of the first switch 2 to cross point B' of the first switch 2', the cross point in the first switch 2'
Switching noise occurs due to switching from A' to cross point B', and switching noise occurs due to switching from cross point a to cross point b in the second switch 3. These two switching noises are caused by the switching timing of the cross points (A' to N') in the first switch 2' and the switching timing of the cross points (a to n) in the second switch 3. In the same case, the two switching noises overlap as shown in FIG.
This value is twice the switching noise caused by switching between the two.

In the present invention, in the control circuit in the video signal switching circuit, the switching timing of the plurality of first switching devices (2 to 2 ⁿ ') and the switching timing of the second switching device 3 are inverted by the inverter 5. There is. In this way, the plurality of first switches 2 to 2 ⁿ ' are switched at the leading edge of the switching clock pulse, and the second switch 3 is switched at the trailing edge of the switching clock pulse, thereby reducing switching noise. appears twice as shown in Figure 7, but the absolute value can be suppressed.

[Effect of idea]

As explained above, in the present invention, the switching timing of the plurality of first switching devices and the second switching device in the video signal switching circuit is set such that the plurality of first switching devices are set at the leading edge of the switching clock pulse. By switching the second switch at the trailing edge of the switching clock pulse,
This has the effect of suppressing an increase in the absolute level of switching noise that occurs during switching.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of an embodiment of the present invention, Fig. 2 is a conventional system diagram, Fig. 3 is a circuit diagram of the cross point output terminal, and Figs. 4 and 5 are the cross point switching timing. 6 is a waveform diagram of switching noise according to the conventional method, and FIG. 7 is a waveform diagram of switching noise according to the present invention. DESCRIPTION OF SYMBOLS 1... Video signal switching circuit, 2... First switching device, 3... Second switching device, 4... Control circuit, 5...
...Inverter, 6...Output terminal.

Claims (1)

[Scope of utility model registration request] a second switch comprising a plurality of first switches each including a plurality of cross points, the second switch receiving the output of the plurality of first switches at an input terminal; the plurality of first switches; and a control circuit for switching a second switch, wherein the plurality of first switches switch at the leading edge of the switching clock pulse, and the second switch switches at the trailing edge of the switching clock pulse. Features a video signal switching circuit.