An 80 MHz 8th-order bandpass /spl Delta//spl Sigma/-modulator with a 75 dB SNDR for IS-95

Abstract

A fully-differential 8th-order cascade bandpass /spl Delta//spl Sigma/-modulator is presented. The circuit is implemented using only two opamps and operates at a sampling frequency of 80 MHz. The circuit can be used in an IF-receiver to combine frequency downconversion with analog to digital conversion by directly sampling an input signal from an intermediate frequency of 60 MHz to a digital intermediate frequency of 20 MHz. The measured peak SNDR is 75 dB for a 1.25 MHz bandwidth (IS-95). The circuit is implemented with a 0.35 /spl mu/m CMOS technology and consumes 37 mW from a 3.0 V supply.