JFET as an amplifier

JFET can be applied as an amplifier. A small change in the reverse bias on the gate produces a large change in drain current. Therefore, this makes a JFET capable of raising the strength of a weak signal.

Operation of a JFET as an amplifier



During the positive half cycle of the input signal, the reverse bias voltage on the gate decreases which increases the channel width and hence the drain current.
During the negative half cycle of the input signal, the reverse bias voltage on the gate increases which decreases the channel width and hence the drain current.
The result is that a small change in the voltage at the gate produces a large change in drain current. These large variations in drain current produces large output across the load R_L.
In summary, this is how a JFET (Junction Field Effect Transistor) acts an amplifier.