Common source does not saturate in the way that a common emitter does. The latter has a real problen with minority carrier strorage that means that it latches ON for a long time when you try to turn it OFF. This can be controlled by a schottky diode base-collector to prevent the collector going too low.
Vertical mosfets have their own problem with a parasitic bipolar transistor that is capacitavily driven. This has to be taken into account in models of mosfets used in rf amplifiers.
Vertical mosfets have their own problem with a parasitic bipolar transistor that is capacitavily driven. This has to be taken into account in models of mosfets used in rf amplifiers.
Lo impedance active linear gate drive circuitry ie (a biased pushpull lo power emitter follower) usually can drive most vfets to allow 1 mhz zero gain unity> As long as the amplifiers main input is bandlimited at the input stage to something reasonable say -3 db @ 150 khz, audio signals, including a full power 20 khz square wave, wont activate the parasitic varactor(s) in terms of catastrophic failure or unusable stability. It is interesting though that the much higher and non linear Drain to Gate feedback capacitance does actually show up in the THD reading usually to a larger extent than crossover distortion @ 20 khz. A typical all N-ch output stage biased at a quiescent operating current of 50 mA with +/- 50 v rails operating closed loop with say 90 dB of loop correction might deliver roughly (mainly xover thd) .01% thd @ 20 Khz say 3 volts below full rail to rail to swing and rise to a still usable .025 % thd (mainly varactor effect thd) right at the onset of clipping.
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