What is the difference between linear and saturation regions in field effect transistor?
In the linear region, the transistor has an almost linear I
versus V curve, which means that as you increase drain-source
voltage, current changes proportionally, e.g. to a loose
approximation, the FET behaves like a resistor, whose resistance is
set by the gate-source voltage. In the saturation region, the I vs
V curve looks like a horizontal line (almost) so it acts like more
like a switch (neither of these analogies is exact, but they give
the general idea).