How to extract level 1 DC parameter for MOS

[Blilix]

Hi,
I wonder how analog circuit designers start their design since in the real situation, mos model is not level 1 model. How do analog designers extract level 1 model parameter? I tried to do this one but I have a problem that the value of the Kn' and Kp' are not constant. They vary with the Vds and Vgs and ratio of W/L so I don't know which value I should use for my initial design. We learn from the textbook that always gives us the value of Kn', Kp', lambda, Vth0 for doing hand calculation but in the real case we need to extract these values by ourselves and they are not constant. Please give me some experience or any suggestion about how to start the analog circuit design from hand calculation.

Thank you so much in advance.

 

[kishore2k4]

Just characterise the MOS transistor for a bunch of different W/L's and take an average, 3-sigma etc. The thing is that the accuracy doesn't matter much. As you said it varies all over the place. Once you decided on some values just go ahead and do your hand-calculations. You'll find that the DC-OP values are not exactly what you expected so you start tuning it(chaning W/Ls, resistors, capacitors etc) until your circuit meet all the specs.

Or you can compute(more or less) those values from the BSIM models. You can find Kn, Kp from Tox and mobility etc.