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Is it necessary for an NMOS to satisfy Vds>=Vgs - Vth to be in saturation

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sumanth gudaparthi

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Hello,
I was doing some circuit in cadence and i suddenly noticed that the NMOS is in saturation but the condition of saturation Vds>= Vgs-Vth is not met..
Instead Vds is less than Vgs-Vth and still it is in saturation.

My Vds = 0.4617 V
Vgs = 1.16
L = 180nm
W = 240nm

Please some one help me in this problem.
 

A bipolar transistor is saturated when it is turned on hard. But a Mosfet is called "ohmic" or "linear" when it is turned on hard and is called "saturated" when it is active.
So maybe your Mosfet is turned on hard and is not saturated.
 

i think your old mosfet is short try a new one... or connect a resistor 10k with gate and other terminal of reistor is connect to ground ...... ur problem will solve ....
 

Re: Is it necessary for an NMOS to satisfy Vds>=Vgs - Vth to be in saturation

Audioguru said:
A bipolar transistor is saturated when it is turned on hard. But a Mosfet is called "ohmic" or "linear" when it is turned on hard and is called "saturated" when it is active.
So maybe your Mosfet is turned on hard and is not saturated.
Click to expand...

i've done the same circuit in cadence umc 180nm technology but still it is showing region:2, which to my knowledge is saturation region.
i dont understand the point in this..

https://obrazki.elektroda.pl/2951572500_1384077971.png

The above is the screenshot of my execution in cadence..

- - - Updated - - -
 

Your apparently assuming a Vdsat value given by the basic quadratic MOSFET model. But as shown in your post, the simulator is calculating a different (lower) Vdsat value.

Refer to your MOSFET textbooks and Spectre device model equations to learn how Vdsat is calculated for the respective transistor model.
 

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