Analog Multiplexer?

A big difference between analog and digital multiplexers is that the former can be used bidirectionally, while the latter are unidirectional. That means that analog multiplexers can also be used as demultiplexer, while for digital you need separate ICs for that.
There are also several types, depending on the number of in/outputs:

multiplexers (non-exhaustive)
8-input: 74HC151, 74HC251,
dual 4-input: 74HC153, 74HC253,
quad 2-input: 74HC157, 74HC257.

demultiplexers (non-exhaustive)
3-to-8 inverting: 74HC138,
3-to-8 non-inverting: 74HC238,
dual 2-to-4: 74HC139.

You can probably use an analog multiplexer as a digital one.

In actuality, in many cases you can use some types of “digital” multiplexor as an analog one, too. People build extremely high performance radios using digital bus switches as commutating RF mixers.

There are basically two ways to do a multiplexor – one is as a choice made of passive switches, basically MOSFET “pass gates” which ideally alter the signal as little as possible when passing through them.

The other is to build a multiplexor using logic gates (or PLD LUT’s) to implement a truth table. This would most likely have the usual logic-gate property of non-linear amplification, ie, an input which just barely qualifies as a 1 or a 0 becomes an output which is quite strongly and unambiguously that value, restoring noise margins.

Leave a Comment