# Difference between overdrive voltage and pinch-off voltage

#### Mark_

Oct 20, 2015
4
overdrive voltage Vov = VGS - VT
pinch-off voltage VDSAT is also VGS - VT
are they the same thing or I am making some mistake on the concept?

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
12,898
VGS-VT expresses the voltage difference between gate voltage and threshold voltage.
When VGS-VT is greater than 0V, the gate is driven to more than the required gate voltage to turn on, it is overdriven. See Wikipedia.
Pinch off voltage is the drain voltage where saturation starts, that is where VDS=VGS-VT, see Wikipedia.

The difference is that VOV is measured between gate and source, VDS between drain and source.

#### Mark_

Oct 20, 2015
4
VGS-VT expresses the voltage difference between gate voltage and threshold voltage.
When VGS-VT is greater than 0V, the gate is driven to more than the required gate voltage to turn on, it is overdriven. See Wikipedia.
Pinch off voltage is the drain voltage where saturation starts, that is where VDS=VGS-VT, see Wikipedia.

The difference is that VOV is measured between gate and source, VDS between drain and source.
Thanks a lot!

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