The GATE Grind

GATE 2016 EC (EC2) – Question 22

Electronic Devices · P-N Junction and Semiconductor Devices · 1 mark · Multiple choice

A long-channel NMOS is biased in the linear region with $V_{DS}=50$ mV and used as a resistance. Which statement is NOT correct?

  1. Increasing width W decreases the resistance.
  2. Reducing threshold voltage decreases the resistance.
  3. Increasing length L increases the resistance.
  4. Increasing gate-to-source voltage increases the resistance.

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Correct answer: (D) Increasing gate-to-source voltage increases the resistance.

Explanation

For small $V_{DS}$, the channel conductance is approximately $\mu_n C_{ox}(W/L)(V_{GS}-V_T)$. Resistance is its reciprocal.

Larger W or greater gate overdrive reduces resistance, while larger L raises it. Reducing threshold voltage also raises the overdrive. Therefore increasing $V_{GS}$ decreases, rather than increases, the resistance. The incorrect statement is **D**.

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