MOSFET

What is the condition for a long-channel nMOSFET to operate in the saturation region? (Assume VGS > Vth.)

  1. AVDS = 0
  2. BVDS < VGS − Vth
  3. CVDS ≥ VGS − Vth
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Answer: C. VDS ≥ VGS − Vth

With VGS > Vth and a channel present, once VDS ≥ VGS − Vth the channel pinches off at the drain end and the drain current becomes nearly independent of VDS. This is the saturation region. When VDS < VGS − Vth, the device is in the linear (triode) region.

  • A. With VDS = 0, no current flows.
  • B. VDS < VGS − Vth is the condition for the linear region.
  • C. Correct. This is the condition for pinch-off at the drain end.
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More MOSFET questions

  1. How does the threshold voltage change when the impurity concentration of the channel region (p-type substrate) of an nMOSFET is increased?
  2. If the gate insulator of an nMOSFET is made thicker with all else unchanged, how does the magnitude of the threshold voltage generally change?
  3. 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?
  4. Which correctly describes punch-through in a MOSFET?
  5. In a pass transistor (switch) made of a single nMOSFET with its gate at the supply voltage VDD, how high does the output rise when passing an input of VDD?