I'm trying to measure the impedance of a 15 pF capacitor with AD5933, but I'm having some problems. I'm using a 220k resistance for RFB and 220k for Z to calibrate. After calibration, I moved the 220k out of Z and leave the 220K still in the RFB. Then, I put the 15 pF capacitor in Z and start the single measurement. The excitation frequency is from 43000 - 48000 Hz.The results I'm obtaining are strange. The phase should be near to -90º and Z should be near to 220 k.The results are in the following images.
Can anyone give me help on this? Thanks.