Naming the gain parameters for BJT versus JFET devices In low-frequency small-signal models, the current gain of a bipolar junction transistor (BJT) is typically denoted by beta (β), whereas the primary gain parameter used for a junction field-effect transistor (JFET) is called ________.

Introduction / Context:Although BJTs and JFETs are both transistors, they are modeled with different primary gain parameters. BJTs are current-controlled devices, while JFETs (and MOSFETs) are voltage-controlled devices modeled by transconductance. Recognizing these parameters helps in predicting amplifier behavior and in translating between BJT and FET design techniques.

Given Data / Assumptions:

• BJT small-signal model uses base current and collector current with β = ic / ib.
• JFET small-signal model uses gate-source voltage to modulate drain current with gm = di_d / dv_gs.
• Low-frequency, midband, small-signal conditions are assumed.

Concept / Approach:BJT: β (also h_fe) is the ratio of collector current to base current. It captures how effectively base current controls collector current. JFET: transconductance gm defines how much the drain current changes for a given small change in gate-source voltage, making it the dominant parameter for voltage-to-current conversion in gain calculations.

Step-by-Step Solution:

Verification / Alternative check:In hybrid-pi models, BJT’s transconductance g_m,BJT = IC / VT also exists, but β remains the familiar current gain parameter. For JFETs, the equivalent “β” is not standard; gm is the central descriptor.

Why Other Options Are Wrong:

Common Pitfalls:Equating β across devices; FETs are controlled primarily by gate voltage and characterized by gm.

Final Answer:beta, transconductance (gm)