JPH0360213A - High frequency signal switching system 2 - Google Patents

Abstract

PURPOSE:To obtain the signal switcher of good isolation in high frequency by cutting off an input signal at the time of the off state of an analog switch. CONSTITUTION:A decoder 13 decodes inputs 14,15 of two bits, and generates the switching signal of the analog switches 8 to 11, and a switched signal is outputted from an output driver 15. Then, the output of the decoder 13 is connected to input butters 5' to 7', and in the input buffer not switched, the signal comes to be cut off. Since the input signal is cut off at the time of the off state of the analog switch, the unnecessary signal level of the analog switch being in the off state is lowered. Thus, the isolation of a whole system can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal switch that switches a plurality of signals to output one signal, and particularly relates to a signal switch that switches high frequency signals.

[Prior Art] Conventional signal switching devices have been based on switching by relays or analog switches.

[Problems to be solved by the invention] Regarding the conventional technology, those using relays have good isolation at high frequencies, but the operation time and recovery time are long, each requiring several times, and the ones using analog switches have a long operation time. Although it is short at only a few ions, it has the disadvantage of poor isolation at high frequencies.

The present invention aims to improve this problem and provide a signal switching device with short operating time and good isolation at high frequencies.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a device that switches a plurality of input high-frequency signals and obtains one output signal, and is provided with a circuit that cuts or turns off each input signal. , the input signal is cut and turned off when the analog switch is turned off.

[Effects of the Invention] With the above configuration, the unnecessary signal level of the analog switch that is turned off is reduced, so that the isolation of the entire system is improved. Also, the switching time is several 10
．． Since it can be made as short as ns, it is easy to synchronize the switching timing with other signals.

[Example] Examples will be described with reference to the drawings.

FIG. 1 is a block diagram of a part of a conventional signal switcher that switches between a video signal, a synchronization signal, and an audio signal, and shows a video signal switching section.

1, 2, and 3 are high frequency signal inputs, and 4 is an output. 5
．． 6.7 is an input buffer.

8.9.10.11 is an analog switch, and 12 is an output amplifier. 13 is a decoder, 2-bit input 14
．． 15 to decode the analog switch 8.9.10.
11 switching signals are generated. The switched signal is output from the output driver 15.

One of the outputs of the decoder 13 becomes "0" due to the 2-bit signal 14.15. Inverters 16, 17, and 18 are connected to the output of the decoder 13, and the output becomes the control input of each analog switch, and the output of the decoder 13 becomes "0". One of the analog switches turns on. Therefore, the inputs 1, 2, 3 and the ground (one of the unmanned cans are connected to the output amplifier 12, and outputted from the output 4).

FIG. 2 is a block diagram of a part of a signal switcher for switching between a video signal, a synchronization signal, and an audio signal according to the present invention, and shows a video signal switching section.

The difference from the conventional example is that the input buffers -5, 6', 7'
The output of the decoder 13 is connected to the output buffer, and the signal is cut off at input buffers that are not selected. Figure 3 is a wiring diagram showing an example of an input buffer, in which 20 is a video input, a resistor 22 and a transistor 23 are connected to the output 21 of the emitter follower, and the midpoint 24 is connected to the output 21 of the emitter follower.
and the input 25 of the output amplifier.

When the switching signal 27 is "1", the output of the inverter 28 is "O" and the analog switch is turned off. At this time, the transistor 23 is turned on, and the input 24 of the analog switch 26 is short-circuited by the transistor 23.

When the switching signal 27 is 0", the output of the inverter 28 is "1", and the analog switch is turned on. At this time, the transistor 23 is turned off, and the input 24 of the analog switch 26 is not short-circuited by the transistor 23.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a part of a conventional signal switcher that switches between a video signal, a synchronization signal, and an audio signal, showing the video signal switching section. FIG. 2 is a block diagram of a part of a signal switcher for switching between a video signal, a synchronization signal, and an audio signal according to the present invention, and shows a video signal switching section. FIG. 3 is a wiring diagram showing an example of an input buffer.

Claims (1)

[Claims] A high-frequency signal switching system in which a device that switches multiple input high-frequency signals and obtains one output signal is provided with a circuit that cuts or turns off each individual input signal, and is configured so that the input signal is cut or turned off when an analog switch is turned off.