how to calculate MOSFET current from spice parameters

[bittersweet]

vdsat mosfet

hi, i want to calculate MOSFET's drain current with hand calculation equations but i must use spice parameters. the problem is spice results and hand calculations are quite different from each other, it is a short channel mosfet (L=0.25 micron) and i calculate kn' and VDSAT wrongly

i use kn'=U0*Eox/Tox
VDSAT=L*Ecritical
Ecritical=VSAT/U0

spice parameters
**************
+ LEVEL=8
+ VERSION=3.1
+ TNOM=27
+ TOX=5.714285714e-09
+ XJ=1e-07
+ NCH=2.3549e+17
+ VTH0=0.3894430714286
+ K1=0.4607149142857
+ K2=0.0044560908571
+ K3=0.001
+ K3B=2.9213062714286
+ W0=1.628242929e-07
+ NLX=2.158731786e-07
+ DVT0W=0
+ DVT1W=0
+ DVT2W=0
+ DVT0=0.4637479857143
+ DVT1=0.5152846714286
+ DVT2=-0.473167907143
+ U0=302.35959485
+ UA=-1.187018e-09
+ UB=2.409610786e-18
+ UC=3.591564071e-11
+ VSAT=148299.19285714
+ A0=1.7430461785714
+ AGS=0.3091595714286
+ B0=-4.28894884e-07
+ B1=3.231547614e-06
+ KETA=-0.00500870045
+ A1=8.867232143e-05
+ A2=0.4381143357143
+ RDSW=151.78334792857
+ PRWG=0.47286105
+ PRWB=-0.199730828571
+ WR=1
+ WINT=0
+ LINT=7.858396571e-09
*+XL=2.785714286e-08
*+XW=-4e-08
+ DWG=-1.45605005e-08
+ DWB=3.402477071e-09
+ VOFF=-0.099706928571
+ NFACTOR=1.7112586714286
+ CIT=0
+ CDSC=0.00024
+ CDSCD=0
+ CDSCB=0
+ ETA0=0.0053021314286
+ ETAB=0.0004532790429
+ DSUB=0.0355151571429
+ PCLM=1.8027351071429
+ PDIBLC1=0.9996565
+ PDIBLC2=0.0026522332857
+ PDIBLCB=-0.071607016786
+ DROUT=0.9301465571429
+ PSCBE1=79836599285.714
+ PSCBE2=5.002775357e-10
+ PVAG=0.0184646143571
+ DELTA=0.01
+ RSH=4.5142857142857
+ MOBMOD=1
+ PRT=0
+ UTE=-1.5
+ KT1=-0.11
+ KT1L=0
+ KT2=0.022
+ UA1=4.31e-09
+ UB1=-7.61e-18
+ UC1=-5.6e-11
+ AT=33000
+ WL=0
+ WLN=1
+ WW=0
+ WWN=1
+ WWL=0
+ LL=0
+ LLN=1
+ LW=0
+ LWN=1
+ LWL=0
+ CAPMOD=2
+ XPART=0.5
+ CGDO=5.611071429e-10
+ CGSO=5.611071429e-10
+ CGBO=1e-12
+ CJ=0.0017497448571
+ PB=0.99
+ MJ=0.4584162428571
+ CJSW=3.934270429e-10
+ PBSW=0.9700637642857
+ MJSW=0.3475086357143
+ CJSWG=3.29e-10
+ PBSWG=0.9700637642857
+ MJSWG=0.3475086357143
+ CF=0
+ PVTH0=-0.008939066929
+ PRDSW=-10
+ PK2=0.0027524210714
+ WKETA=0.0061991008571
+ LKETA=-0.006374305357
+ )

can u help me what is wrong from my calculations

 

[Mahavir]

pspice mosfet parameters

Well, it is not possible to get exactly the same result for current through hand calculations as to the value you get through spice, because spice involves much more complex equations.
I don't know what results are you getting through hand calculations but according to me +- 5% variations to the spice results are okay. Just you need to be careful about the region of operation whether triode or saturation and accordingly consider second order effects as far as possible in the equations for Id.

 

[bittersweet]

mosfet vdsat

unfourtanetly not +-%5 variations in my results, for ex spice result is 733u my hand calculation is 1.6m so they are quite different, is there any mistake for Mn or VDSAT. i use Mn=U0 and VDSAT=VSAT*L/U0

 

[yschuang]

calculate mosfet

In my opinion, it is almost impossible to calculate what you want correctly. You can do that with a simpilfied level. There is a method named gm/id methodology which uses CAD software to help you design.

 

[bittersweet]

how to calculate kn in mos model

I must use Id=k'*W/L*(VGT*Vmin-Vmin2/2)*(1+lambda*Vds) formula for hand analysis Vmin=min(VGT,Vds,VDSAT) VGT=VGS-VT does anybody know a possible way to find k' and VDSAT correctly

 

[tariq786]

calculate kn

**broken link removed**

see how k is calculated