Low power delta sigma capacitor conversion circuit

Abstract

To accurately measure the micro capacitance, a kind of capacitance conversion circuit that uses a second-order Sigma-Delta modulation technique is introduced, and the measuring range of inductive capacitance is extended by a 4-bit DAC capacitor. The loop oscillator is used to provide the modulator with a 16 kHz square wave signal. Because the circuit has a built-in clock generation circuit, no external clock signal is required outside the chip. Chopping technology is used to reduce the impact of 1/f noise on circuit performance. This capacitance conversion circuit is based on the SMIC 0.18um process, simulated and verified with cadence, MATLAB and other tools. The circuit achieves a capacitance range from 0 to 35pF and consumes 25μA from a 1.2V single supply. The conversion time for one measurement is 15ms, during which the resolution is 4fF and good linearity is achieved.