The transconductance g_m of a JFET is equal to:

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RSMSSB JE Electrical Engineering (Degree) 19 May 2022 Official Paper

Answer 1

Junction Field Transistor

F1 Savita Engineering 2-7-22 D29

JFET is a unipolar voltage-controlled semiconductor device with three terminals: source, drain, and gate.
In JFET, the current flow is due to the majority of charge carriers.
Since only the majority of charge carriers are responsible for the current flow, JFETs are unidirectional.

The transconductance of a JFET is given by:

\(g_m = {Δ I_d \over Δ V_{GS}}\)

where, g_m = Transconductance

I_d = Drain current

V_GS = Gate to source voltage

The drain current in a JFET is:

\(I_d =I_{dss}(1-{V_{GS}\over V_P})^2 \)\(I_d= I_{DSS}({1-{V_{GS}\over V_{p}}})^2\)

Differentiating I_d with respect to V_GS, we get:

\({Δ I_d \over Δ V_{GS}} = 2 I_{DSS}({1-{V_{GS}\over V_{p}}})({-1\over V_p})\)

\(g_m = ({-2 I_{DSS}\over V_p})({1-{V_{GS}\over V_{p}}})\)