FET switches

[Davor]

When FETs are used as switches, there is a difference between mixing-fast switches and power on/off switches. In both cases there is a small charge injected from gate to the channel, but it becomes bothersome only in mixing switches. CMOS switches are usually a bit better because of the charge injection cancelling between the N-channel and a P-channel MOSFETs involved. Sadly, it works well only if the common mode voltage is around the middle between Vdd and Vee.
So for mixing purposes it is good to use some kind of balanced mixer scheme, because charge injection gets cancelled in those.