Inverter-based second-order sigma-delta modulator for smart sensors

Presented is a fully-differential inverter-based switched-capacitor second-order sigma-delta modulator for smart sensor applications. To reduce the supply voltage, the power consumption and the chip area, a simple inverter is used to replace the operational transconductance amplifier in the traditional integrator. The supply voltage can be lower than the summation of the absolute threshold voltages of the PMOS and NMOS transistors in the inverter. The described modulator has been designed and fabricated in AMI 0.5 mu m CMOS process. Measurement shows that it can work under 1.5 V supply voltage and provide 55.39 dB signal-to-noise and distortion ratio (SNDR). Simulation also shows that the modulator can work under 0.7 V supply voltage and provide 59.38 dB SNDR in IBM 180 nm CMOS process.