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Sadegh.j

Sadegh.j

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id = idss (1 - vgs/vp)

What is the EXACT formula of the MOS current when it's in saturation: I know:
I=kn(Vgs'Vt)^2*(1+a*Vds)*.....

Apparantly there is another term in it, could ypu please give me that term?
 

that is the only term i knw..
you can refer this page for more details..

**broken link removed**
 

for the level 1 model of an NMOS,whoch follows the square law,this is the expression,,higher end models,would have a different expression ,check out streetman to find the expression for the 3/2 power law model
 

Sadegh.j said:
What is the EXACT formula of the MOS current when it's in saturation: I know:
I=kn(Vgs'Vt)^2*(1+a*Vds)*.....

Apparantly there is another term in it, could ypu please give me that term?
Click to expand...
Hi
there is no EXACT formula for saturation region.
regards
 

Then let me re-state my question this way, what is the best equation you have seen?
 

I have not seen any coherent description in books.
Below is what I have learned in lectures.

iD=K(vGS-Vp)^2*(1+vDS/VA)

or

iD=IDSS*(1-vGS/Vp)^2 ,

where IDSS=K*Vp^2*(1+vDS/VA)

or

IDSS=IDSSM*[(1+vDS/VA)/( 1+VDSM/VA)]

where IDSSM is the IDSS measured by manufacturer at a specific VDS, VDSM.

IDSSM= K*Vp^2*(1+VDSM/VA)

K= IDSSM/[Vp^2*(1+VDSM/VA)]

Note that for normally-off MOSFETs, IDSS is defined for VGS=2Vt.
 

Interestingly, I found the equation (2.29) given in
the David Hodges's book is quite charming which
unifies and distinguishes the short-channel and long-channel.

I personally prefer to use square law to understand
the behavior of the circuit due to its simplicity and
for design, gm/ID and scaling method.
 

I think the expression depends on the level of modelling au r using and the simplicity u want..
if u want simplicity u can discard lambda effect....provided its long channel device....but here little bit error would b there..
if u want accuracy w/o any problem abt complexity..u can consider that one also..
 

Hi,

if you just want to gain some intuition of a circuit, the equation you posted before is good enough for 1st order analysis.
 

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