MOSFET

When a long-channel MOSFET operates in the saturation region, the drain current ID is roughly proportional to what? (VGS: gate-source voltage, Vth: threshold voltage)

  1. AThe square of (VGS − Vth)
  2. BVGS − Vth
  3. CThe reciprocal of VGS
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Answer: A. The square of (VGS − Vth)

In the saturation region of a long-channel MOSFET, ID = (1/2) μ Cox (W/L) (VGS − Vth)², so the drain current is proportional to the square of (VGS − Vth). In short-channel transistors, velocity saturation and other effects cause deviations from this square law.

MOSFET drain current versus drain voltage Drain-source voltage VDS Drain current ID ,,1 ,,4 ,,9 VGS − Vth = 3 V = 2 V = 1 V Linear Saturation Saturation current ∝ (VGS − Vth)²
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More MOSFET questions

  1. For nMOS and pMOS transistors of the same size, the nMOS generally has a larger drive current. What is the main reason?
  2. In an n-channel MOSFET, what happens to the threshold voltage when a negative voltage is applied to the substrate (body) relative to the source (body bias)?
  3. Which is a characteristic of a depletion-mode MOSFET?
  4. Which value is closest to the theoretical lower limit of a MOSFET's subthreshold swing at room temperature (the gate voltage needed to change the drain current by one decade below threshold)?
  5. How does a MOSFET behave in the linear region, where the drain-source voltage VDS is sufficiently small?