A 0.8 V Supply- and Temperature-Insensitive Capacitance-to-Digital Converter in 0.18-mu m CMOS

Abstract

A low-voltage, low-power, capacitance-to-digital converter (CDC) that is insensitive to supply and temperature variations is presented in this paper. The CDC comprises two matched RC oscillators and a counter-based programmable digital converter. The transfer function of the proposed CDC is a scaled ratio of the capacitors having equal drift coefficients, making it insensitive to supply as well as temperature variations. Worst case temperature-dependent drift of +/- 153.4 ppm/degrees C is measured between -40 and +120 degrees C while worst case supply-dependent drift of +/- 1.12% is measured between 0.8 and 1.2 V over full-scale capacitance range. The proposed CDC achieves 2.05 fF resolution, consuming 23 mu A from a 0.8 V supply, at a full-scale range of 3.36 pF. The CDC, realized in 0.18-mu m CMOS process, has an active area of 0.102 mm(2) and offers a scalable resolution within a range of 2-13 b