High-accuracy circuits for on-chip capacitance ratio testing or sensor readout

Novel CMOS circuits are described for the on-chip measurement of capacitor ratios. They can provide a high-accuracy A/D interface for capacitive sensors, or allow the precise calibration of switched-capacitor DACs, amplifiers and other circuits utilizing ratioed capacitors. Various structures are proposed and the limitations of their accuracy are analyzed. Computer simulations illustrate the operation and verify the anticipated robustness and high accuracy of the system even in the presence of nonidealities.>