GATE 2014 EC (EC4) – Question 48
A common-base BJT amplifies a signal from a 50 Ω antenna. With kT/q = 25 mV, find collector bias current (mA) that matches amplifier input impedance to the antenna.
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Correct answer: 0.49 to 0.51
Explanation
The common-base small-signal emitter input resistance is approximately1/gm=VT/IC for high current gain. Set it to50Ωwith VT=25mV:IC=0.025/50=0.0005A=**0.5mA**. This uses the standard neglect of finite-βand external-bias loading corrections.