JFET cutoff definition: Is VGS(OFF) the magnitude of gate-to-source voltage required to reduce the JFET drain current essentially to zero (turn the device off)?

Introduction / Context:Key JFET parameters include IDSS and VGS(OFF). Together they describe the transfer characteristic and are used in bias calculations. VGS(OFF) is the gate-to-source voltage at which the channel is fully pinched off and the drain current approaches zero (cutoff).

Given Data / Assumptions:

• Normal operation keeps the gate-channel junction reverse-biased.
• VGS(OFF) has opposite polarity to IDSS sign convention (e.g., negative for n-channel).
• Shockley equation applies in the saturation region.
• “Essentially zero” means only leakage remains.

Concept / Approach:The depletion regions from the gate junction widen with increasing |VGS|, narrowing the channel. At VGS(OFF), the channel is pinched off across its entire length, stopping conduction apart from leakage. This is the end-point on the transfer curve opposite IDSS (at VGS = 0 V).

Step-by-Step Solution:

Verification / Alternative check:Datasheet transfer curves mark cutoff at VGS(OFF) where ID is near the leakage floor, confirming the interpretation.

Why Other Options Are Wrong:

Common Pitfalls:Confusing VGS(OFF) with MOSFET threshold; missing sign conventions; using ID ≈ 0 without accounting for leakage in precision designs.

Final Answer:Correct