A high-precision capacitance sensor based on direct digital synthesis technology

This paper demonstrates a high precision capacitance measurement method based on digital modulation and demodulation that are achieved by direct digital synthesis technique. The accuracy of the measurement circuit is limited by the accuracy of the excitation source and the stability of the reference signal of PSD. A high stability excitation source depending on digital modulation is developed by analyzing the factors that influence the waveform, such as, discretization noise, phase shift resolution and performance error of DAC. The digital demodulation based on DDS has significant advantage over the conventional PSD without the problems concerning the amplitude and phase shift stability of the analogue reference signal.