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Given the value of Vgs, Vds and Id for a pmos, how to determine the mode of operation and its Vt

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Generally in case of NMOSFET,

  • Vgs < Vt - Weak Inversion
  • Vgs > Vt - Strong Inversion

In each (Weak or Strong Inversion), if

  • Vds < Vgs-Vt, its in Linear(or Triode) region
  • Vds > Vgs-Vt, its in Saturation Region.

Whereas in PMOS, we have to invert the symbols because the voltage is opposite (Source is positive with respect to Drain). Even Threshold voltage is negative for PMOSFET (-Vt)

So, for PMOSFET:

  • Vsg < Vt - Weak Inversion
  • Vsg > Vt - Strong Inversion

In each (Weak or Strong Inversion), if

  • Vsd < Vsg+Vt, its in Linear(or Triode) region
  • Vsd > Vsg+Vt, its in Saturation Region.
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If Vds < Vgs, its triode (resistive). Otherwise in saturated regions.

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