This multiplexer switch circuit is built with the IC 4066 and was designed to switch multiple signal sources into a single common output and can be used as a replacement for the conventional mechanical switches.
Conventional multiplexer switches hava an annoying disadvantage that the video signals mix over when the source is changed but this circuit avoids this problem by disabling the inactive signal line.
The heart of the switch is a digitally controlled analog switch 4066. The switches are ES1 … ES8 and each 4066 contains 4 switches. When channel 1 is selected, ES1 and ES2 are closed and ES3 is open. Channel is suppressed at this moment since ES5 and ES6 are open and ES7 prevents cross-over between the two channels by grounding the channel 2 line.
The bandwidth of the multiplexer sw circuit is around 8 MHz. The current consumption is 1 mA. A high level power supply voltage level is required since the input impedance level of the circuit drops with higher voltage levels.
When the multiplexer circuit is connected to a 75 Ω impedance load, some signal losses will result due to the internal resistance of the switches. This can be compensated by connecting a video amplifier at the output.
Article submitted by Michael Gregory – Romania.