Difficulty: Easy
Correct Answer: reverse-biased
Explanation:
Introduction / Context:Unlike BJTs, a JFET is a voltage-controlled device with a reverse-biased gate junction (for JFETs with p-n junction gates). This creates a depletion region that modulates the channel cross-section and allows linear small-signal control of drain current by gate-source voltage without significant gate current.
Given Data / Assumptions:
Concept / Approach:A reverse-biased gate-source junction widens the depletion region, controlling channel conduction without injecting carriers across the junction. Small variations in vgs around the bias point vary the channel conductance, producing a proportional change in drain current id = gm * vgs (small-signal), with gm determined by the bias point.
Step-by-Step Solution:
Bias the gate negative relative to source (for n-channel) or positive (for p-channel) to ensure reverse bias.Set the quiescent point so that vgs is below pinch-off but not too close to cutoff, to allow signal swing.Confirm minimal gate current (practically zero in reverse bias), ensuring high input impedance.Operate within the ohmic-to-saturation region appropriate for the chosen topology.Verification / Alternative check:Measure gate current with a sensitive meter; in proper reverse bias it will be microamps to nanoamps. Any forward bias will increase gate current dramatically and distort the signal.
Why Other Options Are Wrong:
forward-biased / neutral: would allow significant gate current, destroying the high input impedance and linearity.either forward-biased or reverse-biased / forward-biased only at high frequency: incorrect; proper linear operation requires reverse bias regardless of frequency.Common Pitfalls:Confusing MOSFET insulated-gate behavior with JFET p-n gate junction behavior. A MOSFET gate is insulated; a JFET gate is a diode junction that must be reverse-biased.
Final Answer:reverse-biased
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