# Threshold and pinch-off voltages for N-channel depletion MOSFET

I am confused about the MOSFET parameters. Consider a depletion N-channel MOSFET. Suppose the gate-source (Vgs) threshold is Vth = -2V, in its off position. Suppose we have not reached the threshold and we are at Vgs = -1 V. This means that the MOSFET will conduct when a voltage Vds is applied (let Vds = +3 V to drain). There also exists the pinch-off voltage Vp beyond which saturation occurs.

Actual datasheets seem to suggest that Vth and Vp are independent of each other, yet I have seen statements such as Vds > Vgs - Vth. I am not sure if Vp = Vgs - Vth, as some discussions seem to suggest.

The threshold voltage is the gate-source voltage $$\V_{GS}=V_{Th}\$$ at which drain-source charge flow begins.
The pinch-off voltage is a drain-source voltage $$\V_{DS}=V_{PO}\$$ at which saturation occurs. Definitely independent from $$\V_{Th}\$$.
(updated) However, the pinch-off voltage is dependent on $$\V_{GS}>V_{Th}\$$ as shown in the image clipped from Dr. Bakr's lecture notes below.
• @Roger: Not at all. The voltage $V_{DS}$ has no effect on $V_{GS}$. All $V_{GS}$ does is modulate the channel resistance. There is no $V_{DS}$ unless there is drain current or a supply voltage Commented Nov 23, 2022 at 3:16