Hi,
I'm miserable on trying to do a hand calculation during design. Most of the time, we try to start determine the proper W/L for a transistor using Id=k/2(W/L)(Vgs-vth)^2 depending the operating region desire to operate at. The problem arise here is, in the model file, the k or betaeff output from spectre is a changing value depending on the W/L of the transistor (or based on model selector). I did tried to make a thorough calculation based on bsim3v3 equation to calculate vth, vdsat etc refering to manual from cadence and bsim, yet still some mismatch arise, is it I miss out the homotopy calculation that simulator did? Can anyone point me out how spectre come out with these values for dc operating points, equation should be great if anyone can share it here. The purpose of matching the value is to aids in first hand calculation to determine the approximate W/L which I feel will increase my confidence on the dimension I had chosen and also countercheck on the result. This is the way designer should work. Any advice to offer? Thanks in advance!
signal            OP("/I0/NM9" "??")
betaeff             414.964u        
cbb                 133.768f        
cbd                   7.22042a      
cbg                 -48.4775f      
cbs                 -85.2974f      
cdb                 -75.4017a      
cdd                   3.80463f      
cdg                  -3.93929f      
cds                 210.058a        
cgb                 -56.412f        
cgd                  -3.76909f      
cgg                 221.473f        
cgs                -161.292f        
cjd                  10.1642f      
cjs                  12.3906f      
csb                 -77.2802f      
csd                 -42.7591a      
csg                -169.057f        
css                 246.38f        
gds                  17.2005n      
gm                   22.5107u