The transconductance gm of a BJT in active region with collector current IC and thermal voltage VT is which?
Agm = IC / VT
Bgm = VT / IC always
Cgm = IB / β only
Dgm = VBE / VT only
Answer & Solution
Correct answer: A. gm = IC / VT
Small-signal BJT: gm = ∂IC/∂VBE = IC/VT. At IC=1 mA, gm ≈ 40 mA/V. Key parameter for small-signal voltage gain in CE amp.
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