The GATE Grind

GATE 2022 EC – Question 28

Digital Circuits · Combinatorial Circuits · 1 mark · Multiple select

Select the correct statement(s) regarding CMOS implementation of NOT gates.

  1. Noise Margin High ($NM_H$) is always equal to the Noise Margin Low ($NM_L$), irrespective of the sizing of transistors.
  2. Dynamic power consumption during switching is zero.
  3. For a logical high input under steady state, the nMOSFET is in the linear regime of operation.
  4. Mobility of electrons never influences the switching speed of the NOT gate.

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Show answer and explanation

Correct answer: (C) For a logical high input under steady state, the nMOSFET is in the linear regime of operation.

Explanation

With a logic-high input the output is pulled to 0 V, so the nMOSFET has $V_{DS}\approx0$ and works in the linear (triode) region: C is correct. $NM_H=NM_L$ only for a symmetric sizing (A is false), switching always dissipates dynamic power $CV^2f$ (B false), and the electron mobility sets the nMOSFET current and hence the speed (D false).