GATE 2024 IN – Question 24
The figure shows an NMOS amplifier. The transistor operates in saturation with $\mu_n C_{ox}=250\ \mu\mathrm A/\mathrm V^2$, $V_T=0.65$ V, and $W/L=4$. Neglect channel-length modulation. Its operating-point drain current is ______ μA (nearest integer).
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Correct answer: 498 to 502
Explanation
No DC gate current flows, so $V_G=V_D=3.3-3300I_D$. The saturation equation is $I_D=\tfrac12(250\times10^{-6})(4)(V_G-0.65)^2$. Substitution of $I_D=500$ μA gives $V_G=1.65$ V and overdrive 1 V, satisfying the equation. Since $V_{DS}=1.65\ge1$ V, saturation is consistent. The other algebraic root has negative overdrive and is invalid.
Answer: **500 μA**.