Abstract: Methods of improving a signal to noise ratio using synchronous rejection are enclosed. Also disclosed are various synchronous rejection systems. In one method of synchronous rejection, the method includes correlating a phase of a reference signal to a phase of the interference signal; collecting a first data set during a first period of time using the reference signal; inverting the reference signal and re-correlating the phase of the reference signal to the phase of the interference signal; collecting a second data set during a second period of time using the inverted reference signal; and integrating the first and the second data set.

Abstract: A capacitance measuring device and method including ratio transformers, a reference capacitor(s), multiplying digital-to-analog converters connected to form a bridge, the converters being adjustable to at least partially balance the bridge, digital signal processor (DSP) for driving and control functions, and feedback to the DSP to maintain and to correct in real time desired amplitudes and phase relation of the signals produced by the ratio transformers. Commutation is used to balance or to average feedback signals to enhance precision, accuracy, resolution and stability. The bridge uses DSP generated phase shifted signals and reference capacitors to balance the real part of the unknown impedance.

Abstract: A capacitance measuring device and method including a ratio transformer, a reference capacitor(s), and multiplying digital to analog converters connected to form a bridge, the converter being adjustable to at least partially balance the bridge. The bridge can further include a 90.degree. phase shifter and reference capacitors to balance the real part of the unknown impedance. An internal calibration scheme calibrates various components of the bridge.