How to measure the total capacitance of mosfets?

[md]

As my graduation project I am designing an on-chip voltage controlled LC oscillator. I am realizing the capacitances using pmos transistors in 0.35um technology. I need to measure the capacitance of the mosfets over a range of control voltages. How can I measure the total capacitance of the mosfets over a range of voltages? I am using A*p*l*a*c 7.60 and O*r*c*a*d 9.2 at home and Cadence Design Framework II at school. All ideas are welcome.

md

 

[Spip4114]

Please PM me, I'll explain it.

 

[rfsystem]

I think to measure the mos capacitance as a function of DC voltage, e.g. the control voltage is supported in most simulators by tracing the internal variables. For oscillators the problem is that if the capacitance curve is nonlinear also the amplitude of the ocillator determinate the frequency. That is most crictical for PMOS caps. At the threshold voltage the cap change by a factor 2x over 100-200mV. If the amplitude varies also the frequency. That is a serious practical problem.