05-11-2016, 11:39 PM
It's an unfortunate choice of words, really, 'saturation!'
Saturation in FETs refers to the region above the Id / Vd 'knee," the opposite of bipolar! And if the FET is driven hard on, as Mike Watterson says, it behaves like a low-value resistor and is (confusingly but, perhaps justifiably) referred to as the "linear region." If you operate the FET so that it enters the linear region, you get clipping on the negative output peaks!
But for valves, BJT's, or FET's, whatever we call it when the , we can't stop it being what it is. And when the thing starts clipping on the negative output peaks, we want to know the details! Bipolar junction transistors tend to clip with the thing dropping maybe a volt, maybe even just 50mV (less than the emitter-base drop!); FET's behave just like a low-value resistor, thus the voltage drop is small but load-current dependent; pentodes and beam tetrodes are even soggier but crudely, 20-40V is not unreasonable.
![[Image: Je7va.png]](http://i.stack.imgur.com/Je7va.png)
Saturation in FETs refers to the region above the Id / Vd 'knee," the opposite of bipolar! And if the FET is driven hard on, as Mike Watterson says, it behaves like a low-value resistor and is (confusingly but, perhaps justifiably) referred to as the "linear region." If you operate the FET so that it enters the linear region, you get clipping on the negative output peaks!
But for valves, BJT's, or FET's, whatever we call it when the , we can't stop it being what it is. And when the thing starts clipping on the negative output peaks, we want to know the details! Bipolar junction transistors tend to clip with the thing dropping maybe a volt, maybe even just 50mV (less than the emitter-base drop!); FET's behave just like a low-value resistor, thus the voltage drop is small but load-current dependent; pentodes and beam tetrodes are even soggier but crudely, 20-40V is not unreasonable.
