Consider an n-channel MOSFET of width $W$, length $L$, channel electron mobility $\mu_n$ and oxide capacitance per unit area $C_{ox}$. Given $V_{GS}=0.7$ V, $V_{DS}=0.1$ V, $\mu_nC_{ox}=100\ \mathrm{\mu A/V^2}$, $V_{TH}=0.3$ V and $W/L=50$, the transconductance $g_m$ (in mA/V) is ________.
First identify the region: $V_{GS}-V_{TH}=0.4$ V, larger than $V_{DS}=0.1$ V. The device is in the linear region, not saturation.
The linear-region current is $I_D=\mu_nC_{ox}(W/L)[(V_{GS}-V_{TH})V_{DS}-V_{DS}^2/2]$. Differentiate with respect to $V_{GS}$ at fixed $V_{DS}$ to get $g_m=\mu_nC_{ox}(W/L)V_{DS}$.
Thus $g_m=100(50)(0.1)=500$ μA/V, or **0.50 mA/V**.
More BJT and MOSFET Amplifiers questions
GATE 2017 EC (EC2) Q24– Consider the circuit shown. Assume base-to-emitter voltage V BE=0.8 V and common-base…
GATE 2017 EC (EC2) Q50– Assume the transistors M1 and M2 in the circuit shown are identical and each has threshold…
GATE 2017 EC (EC2) Q51– In the circuit shown, Q1 and Q2 are each biased at collector current 2.6 mA. Assume their…
GATE 2016 EC (EC2) Q24– Resistor R 1 has been adjusted so that I 1=1 mA. Transistors Q1 and Q2 are perfectly…
GATE 2016 EC (EC2) Q25– Which statement is correct about an ac-coupled common-emitter amplifier operating in the…
GATE 2016 EC (EC3) Q24– For the circuit shown, assume V BE1=V EB2=0.7 V. The dc collector voltage V C2 in volts is…