The channel of a JFET is between the _________

Question

Examoogle · Accepted Answer

Drain and source

Explanation: In a Junction Field-Effect Transistor (JFET), the conducting channel is the semiconductor path through which charge carriers (electrons or holes) flow from the source to the drain. The gate-to-channel junction is reverse-biased to control the width of this channel and thus the current.

Working Principle: The JFET operates by varying the depletion region width at the gate-channel interface. By adjusting the reverse bias voltage $V_{GS}$, the depletion region extends into the channel, narrowing the effective cross-sectional area available for conduction between the drain and the source terminals.

Key Formulas: $I_D = I_{DSS} \left( 1 - \frac{V_{GS}}{V_P} \right)^2$ — Shockley's equation for drain current in saturation region; $g_m = \frac{2I_{DSS}}{|V_P|} \left( 1 - \frac{V_{GS}}{V_P} \right)$ — Transconductance of the JFET

Key Points: The drain-source path forms the resistive channel of the JFET.; The gate electrode controls the channel width via an electric field.; JFETs are voltage-controlled devices, unlike BJTs which are current-controlled.; The channel is formed between the source (S) and drain (D) terminals.

Advantages: High input impedance; Low noise performance; Negative temperature coefficient (prevents thermal runaway)

Disadvantages: Lower gain-bandwidth product compared to BJTs; Sensitive to static discharge (ESD)

Applications: Low-noise amplifiers; Buffer amplifiers; Voltage-controlled switches

Additional Info: A JFET is inherently a depletion-mode device.. Option A is incorrect because the gate acts as the control electrode, not a terminal for the main conduction path.

Answer: B is correct — The channel in a JFET is defined as the conduction path existing between the drain and the source terminals.

Exam Tip: Remember that in FETs, the main current flows through the channel between drain and source, while the gate terminal is strictly used for controlling this flow via electric fields.

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