A closed-loop ΣΔ modulator for micromechanical capacitive sensors

This paper describes a CMOS fully-differential switched-capacitor (SC) single-loop Sigma-Delta (ΣΔ) modulator specialized for highly precise micromechanical capacitive sensors. This design adopts a singleloop, fourth-order, one-bit quantization architecture with feedforward paths for lower nonlinearities and power consumption. Systematic optimization is used to avoid deterioration in conversion accuracy caused by capacitor mismatch. Chopper-stabilization and double-sampling techniques are also employed to enhance performances in noise depression. Manufactured in a standard 0.35μm CMOS process, the ASIC occupies an area of 5.32mm2 including 25 pads. This modulator achieves a signal-to-noise ratio (SNR) of 105.2 dB and dynamic range (DR) of 113.7 dB. The whole chip consumes 12.6mW from a 5V supply.