GATE 2014 EC (EC1) – Question 44
A forward-active BJT has $V_{BE}=0.7$ V, $kT/q=25$ mV and reverse saturation current $I_S=10^{-13}$ A. Find transconductance (mA/V).
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Correct answer: 5.7 to 5.9
Explanation
Use IC=ISexp(VBE/VT)=10⁻¹³exp(0.7/0.025)=0.144626mA. The small-signal transconductance is gm=IC/VT=0.144626/0.025=**5.78503mA/V**. The thermal voltage must be used in volts with VBE.