Q.What is transfer characteristics?

A JFET is described by two families of characteristic curves, both plotted from a single test circuit in which one supply sets the gate-source voltage $V_{GS}$ and another sets the drain-source voltage $V_{DS}$, while the drain current $I_D$ is measured.

Drain characteristics show the relationship between the drain current $I_D$ and the drain-source voltage $V_{DS}$ at a constant gate-source voltage $V_{GS}$. Keeping $V_{GS}$ fixed, $I_D$ is recorded for various $V_{DS}$ and plotted with $V_{DS}$ on the x-axis; repeating for several gate voltages gives a family of curves. A single curve reveals three regions: the ohmic region, where $I_D$ rises almost proportionally with $V_{DS}$; the pinch-off / saturation region, where $I_D$ stays nearly constant; and the breakdown region, where $I_D$ rises steeply due to avalanche effect. The maximum current on the $V_{GS}=0$ curve is $I_{DSS}$. …