CMOS gate as linear amp?

[KX4QC]

Not ideal, but if one has a left-over logic gate and a small signal linear amp is needed, the temptation is great:

Microcontroller Group, Moorabbin, Melbourne
Ref: http://melbmcu.weebly.com/cmos-gate-as- ... ifier.html

CMOS gate as a linear amplifier
By David Stonier-Gibson

There are times when you are making an essentially all-digital circuit, but need a little bit of linear amplification. Examples of this would be a microphone pre-amp for a sound triggered switch, or a photodiode pulse pre-amplifier. I have used this several times throughout my career, when a left over gate can be used instead of having to add another chip to the design. It works with any inverting gate, meaning NAND, NOR or NOT (usually called inverter). NAND and NORs have more than one input. Use one of the inputs, then tie the others to ground for NORs and + supply for NANDs.

Note: This trick will only work with unbuffered CMOS gates or inverters. That means, for 4000-series chips, the ones with a …login to view the rest of this post