A 2.7-mW 145dB-SQNR sigma delta modulator

A high resolution low power sigma delta modulator for analog to digital conversion (ADC) over 20 KHz range is presented. The modulator consists of a fourth order design operating at a baseband frequency of 20 KHz with an oversampling ratio (OSR) of 256. A continuous time active RC loop filter based design is implemented, which achieves a Signal to Quantization Noise Ratio (SQNR) of 145dB leading to a 24 bit resolution of the ADC. A very low power consumption of 2.7 mW at a supply voltage of 1.8V is achieved in 0.18micron CMOS technology. A CIFB topology is chosen to implement the modulator which supports stable operation at large resolution.