This is a capacitance sensor with a resolution down to 5fF. The circuit is based on a switched capacitance technique. The modulated signal is amplified and demodulated in following stages to produde a DC level corresponding to the change in capacitance. This then feeds into an MSP430P320 microcontroller unit, which has an inbuilt ADC. Here, the analog data is processed here and the final result displayed using a serial interface to a computer.

 

Attached is the Pspice files for the circuit without the micro-controller unit. 

The same circuit has been simulated in Multisim and results verified.