In a common-emitter BJT amp with emitter degeneration RE, the voltage gain magnitude (ignoring ro) approximates which?
A|A_v| ≈ β/gm always at every bias
B|A_v| ≈ RE/RC always at every bias
C|A_v| ≈ gm·RE only at every bias
D|A_v| ≈ RC/(RE + 1/gm) ≈ RC/RE
Answer & Solution
Correct answer: D. |A_v| ≈ RC/(RE + 1/gm) ≈ RC/RE
With emitter resistor RE unbypassed: A_v = -gm·RC/(1+gm·RE). For gm·RE >> 1: |A_v| ≈ RC/RE. Trades gain for linearity + bandwidth (negative feedback).
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