I had previously asked about the AD7747 in this discussion and would like to follow up with a revised setup.
The bottom side of the variable capacitor ( < 2pF) is grounded but is connected to two resistors (<2 ohms). As the voltage to the resistors is increased from 0 - 1VDC, the plate separation distance decreases and should increase the capacitance. However, I am not seeing any changes in the measurements.
In my previous setup, the grounded side of the capacitor had some serial resistance leading to voltage differences but in this case, it is directly at the ground potential. Is there something with my design that is preventing the measurement to be made?