The depletion mosfet can also operate in enhancement mode when the gate voltage is positive (say for depletion type NMOS).

My question is :

Will the Shockley equation be still valid in the enhancement mode? or Should we use the equations of enhancement NMOS?

Moreover, if i am driving the depletion type MOS to a an enhancement type MOS under a constant drain source voltage (Vds), say for example:

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In the above case, Vgs is positive and the depletion type MOS is in enhancement mode also Vds > gate voltage ,Does that mean the Depletion MOS is in saturation region of the enhancement mode?

If i neglect Vds here and use current equations of NMOS enhancement type , i get:

Resistance =500 ohms.

But am confused about whether its correct or not and if that's the case why should i neglect Vds ?


1 Answer 1


The only difference between an enhancement mode NMOS and a depletion mode NMOS is the value of Vt for which Id = 0, the formulas are the same.

If you understand how an enhancement NMOS works you could just imagine it having a voltage source in series with the gate and the total will behave as a depletion NMOS !

  • \$\begingroup\$ i agree with Vt thing but are the formulas actually same? depletion mosfet is more like jfet when you try to deplete channel out and shockley's equation is used !! \$\endgroup\$ Nov 23, 2015 at 12:52
  • \$\begingroup\$ Also i wont to know whether for the given Vds and Vgs the depletion mos is going behave like a enhancement mode mos in linear region or not ?! \$\endgroup\$ Nov 23, 2015 at 12:53

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