MOSFET

When a MOSFET is used as a switch, which statement correctly describes its on-resistance?

  1. AThe source-drain resistance when the device is off
  2. BThe resistance of the gate electrode itself
  3. CThe source-drain resistance when the device is on; the smaller it is, the lower the loss
Show answer and explanation

Answer: C. The source-drain resistance when the device is on; the smaller it is, the lower the loss

On-resistance is the drain-source resistance while the MOSFET is conducting. A current I causes an I²R loss, so the smaller the on-resistance, the more efficient the switch. Raising the gate voltage increases the carriers in the channel and lowers the on-resistance.

  • A. The resistance when off is very large and is not called on-resistance.
  • B. The resistance of the gate electrode is called gate resistance, a different thing.
  • C. Correct. It is the drain-source resistance while conducting.
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More MOSFET questions

  1. For a typical MOSFET in an integrated circuit, which statement about the source and drain is correct?
  2. What is the condition for a long-channel nMOSFET to operate in the saturation region? (Assume VGS > Vth.)
  3. How does the threshold voltage change when the impurity concentration of the channel region (p-type substrate) of an nMOSFET is increased?
  4. If the gate insulator of an nMOSFET is made thicker with all else unchanged, how does the magnitude of the threshold voltage generally change?
  5. Which generally describes the relationship between a MOSFET's gate length (the length of the gate electrode on the mask or after patterning) and its effective channel length?