JFET control characteristic: A junction field-effect transistor (JFET) is best described as a device that is:

Introduction / Context:
FETs differ fundamentally from BJTs. In a JFET, the gate-source voltage controls the channel conductivity, and because the gate junction is reverse-biased in normal operation, the input current is extremely small—leading to very high input resistance compared with BJTs.

Given Data / Assumptions:

• JFET used in its linear region for amplification.
• Gate-channel junction reverse-biased (except at breakdown).
• Signal applied as gate-source voltage variation.

Concept / Approach:
The drain current I_D is primarily a function of V_GS (and V_DS), summarized by transfer characteristics I_D = f(V_GS). Since V_GS sets the depletion width and channel cross-section, the device is voltage-controlled and presents very high input impedance at the gate, making it attractive for sensor front-ends and high-impedance nodes.

Step-by-Step Solution:

Verification / Alternative check:
Datasheets specify gate leakage currents in the nanoampere range and input resistance in megaohms to gigaohms, consistent with voltage-controlled behavior.

Why Other Options Are Wrong:

• Current-controlled: Describes BJTs (base current controls collector current).
• Low input resistance: Opposite of the JFET's hallmark property.
• Always forward-biased: Gate is normally reverse-biased; forward bias risks damage.

Common Pitfalls:
Driving the gate positive on an n-channel JFET and inadvertently forward-biasing the junction; always respect V_GS(max) ratings.

Final Answer:
is a voltage-controlled device