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what is "MOSFET bidirectional analogue gate"?


Fritz Schlunder

Jan 1, 1970
nick said:

I presume you are talking about products like the 74VHC4066 for instance.
Datasheet here:

These devices are quite similar electrically to mechanical switches in many
ways. They can pass current in either direction, and they do not
significantly interfere with analog voltages. A regular CMOS digital gate
will normally convert any analog voltage not right at the switching
threshold and produce logic level outputs.

The same basic functionality can be obtained but with superior (for some
purposes) specifications using things like two discrete MOSFETs wired back
to back and their gates bias properly. A practical implementation could be
made by connection the gates together of each device. Both sources would
also be connect together. The drain pins would function as bidirectional
input and output. Somehow you have to drive both gates, and one of the
easiest and more versatile ways would be with a photovoltaic optical
isolator. These devices differ from regular transistor output optical
isolators in that they contain solar cells which actually output a small
amount of useable power.