Self on Audio, 3rd Edition

Chapter 13Electronic analogue switching, Part II: discrete FETs

(Electronics World, February 2004)

The signal handling capabilities of 4000-series analogue gates is limited to about half of what is needed in an opamp-based signal path. You will also have seen from the previous article that good linearity and the ability to handle a full op-amp output swing with these ICs requires the use of current-mode, with a virtual-earth (shunt-feedback) amplifier. This lands with you with an extra op-amp for each switch, which needs power and board space, and gives added noise and distortion in return. It also, crucially, introduces a phase inversion which usually needs to be immediately undone with another op-amp, because the preservation of correct phase ...