What is diference between Vdsat, Vov ,Veffective (Vgh-Vth), and Vds......?

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ASHUTOSH RANE

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HELLO FRIENDS,

I am getting confused with term Vov(ovrdrive voltage) and Veffective (=vgs-vth).......!!
while designing a opamp in cadence i set
Vov of 0.3 for PMOS and
Vov of 0.25 for NMOS.....

the operating point info in Cadence shows Following parameters
Vdasat,
Vds,
Vgs-Vth (can be calculated)
then which i should consider as Vov drive ?:|:?:


The tool shown very different values than the designed one (it is obvious as it Uses BSIM3v3 model )!
 

Overdrige Voltage Vov is identical with effective Voltage Veff and both are equal to Vgs-Vth.

Vdsat is the minimum drain-source voltage needed to ensure that the transistor works in saturation (Vds>Vdsat for sat. otherwise the fet works in triode).

As for Vds i don't think you need explanation...
 
@JIMITO13
Hi friend ,
thank u a lot for reply,
Vds> Veff (book considers this criterion for saturation)
Vds> Vdsat,(tool consider this criterion for saturation ....):roll:
which criterion is most accurate among this?
 

For long channel devices or for devices of older processes with high allowed minimum length Vov(or Veff) equals Vdsat.
Additionally for hand calculations we assume Vdsat=Vgs-Vth for simplicity.
As for simulation and real design the criterion is Vds>Vdsat for saturation.

Take a look at chapter 3.7.3 of David Binkley's excellent book "Tradeoffs and Optimization in Analog CMOS Design" for more in-depth search.
 
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