5 mW, 64 dB SNDR, 4/sup th/ order bandpass /spl Sigma//spl Delta/ modulator for 10.7 MHz digital IF

Abstract

A 5 mW 4th order SC bandpass sigma-delta modulator is designed in 0.8-/spl mu/m CMOS process. An SNDR of 64.8 dB over 200 kHz, and image-rejection better than 80 dB are achieved by adapting double-sampling technique in circulating-delay-type resonator. The resonator is built using a high performance gain-boosted folded-cascode opamp. An improved SC-CMFB circuit is proposed to support double-sampling requirements. The opamp achieves 106 dB of DC gain, 180 MHz GBW with 750 mA at 3 V supply.