Two different methods give me different curves (Cap. vs DC bias voltage). However, initial value, final value and also the capacitance at zero bias voltage for both methods are the same.
I use ADE L to calculate the capacitance of a varactor in a desired frequency. The first method was to use AC analysis. Taking the imaginary part of the current and dividing by frequency(rad/s) is the capacitance calculated by this method. The other method was to simply using SP analysis and then the imaginary part of Y11 divided by frequency(rad/s) would be the capacitance. I sweep the DC voltage across the capacitor and get the same final and middle values from both methods. However the slope of the curve is about 1.9 times different and I cannot guess why and which one I can trust.
Any idea?