GATE 2017 EC (EC2) – Question 50
Assume the transistors M1 and M2 in the circuit shown are identical and each has threshold voltage 1 V. The states of M1 and M2, respectively, are
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Correct answer: (C) Linear, Saturation
Explanation
Let v be the common node: the drain of M1 and source of M2. For M1, $V_{ov1}=2-1=1$ V, so saturation would require $v\ge1$ V.
For conducting M2, $V_{ov2}=1.5-v$ and $V_{DS2}=3-v$. Its saturation inequality is automatically satisfied. If M1 were also saturated, equality of the two currents would give $1=(1.5-v)^2$, hence v=0.5 V on the conducting branch, contradicting $v\ge1$.
The consistent solution instead has M1 linear and M2 saturated. Equating their square-law currents gives $v\approx0.589$ V, which satisfies both regional inequalities. The answer is **C**.