Q.Briefly explain the working of n channel JFET.

The n-channel JFET works by letting the reverse gate-source voltage control the width of the channel and hence the drain current. …

[!TLDR]

In an n-channel JFET the reverse gate-source voltage widens the depletion regions and narrows the channel, so $I_D$ falls from its maximum $I_{DSS}$ (at $V_{GS} = 0$) to zero at pinch off $(V_{GS} = V_P)$.

An n-channel JFET is operated with the drain-to-source supply $V_{DD}$ making the drain positive with respect to the source, and the gate-to-source supply $V_{GG}$ keeping the two gate-channel pn junctions reverse biased. The reverse bias creates depletion regions that extend into the n-type channel.

When $V_{GS} = 0$ (gate at source potential), the depletion regions are narrow, the channel is widest and the drain current is maximum; this maximum current is called $I_{DSS}$ and flows from drain to source. As the reverse gate-to-source voltage is increased, the depletion regions grow and reach further into the channel, reducing its effective width and increasing its resistance, so the drain current $I_D$ decreases. On increasing the reverse bias still further, a stage is reached where the two depletion regions touch each other and completely close the channel; this gate voltage is the pinch off voltage $V_P$, and here the drain current falls to zero. Hence the drain curren …