Does anyone know how to model a depletion mode N channel MOSFET in spice?
I have looked online however the majority of resources have shown how to model a depletion type or enhancement type. I specifically want to model a FET that is fully on when there is a 0 Vgs voltage.
Resources i've looked at
Answer
The solution is given in the LTSpice help file you linked:
VTO is positive (negative) for enhancement mode and negative (positive) for depletion mode N-channel (P-channel) devices.
For an NMOS FET, if VTO is positive, you have an enhancement mode device. If VTO is negative, then you have a depletion mode device.
For a depletion mode NMOS FET, with 0 Vgs the channel will conduct. Vgs must be pulled below 0 V in order to cut off the channel. In SPICE this behavior is represented by a negative threshold voltage, controlled by the VTO parameter.
From your comments, though, you want
When Vgs > Vth the channel will close an only leakage will flow.
To get this behavior, you need a p-channel depletion mode MOSFET. An n-channel FET doesn't work this way.
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