A quadrature direct digital downconverter

Abstract

A quadrature direct digital down converter (DDD) is presented. The converter has a continuous time /spl Delta//spl Sigma/ noise shaping loopfilter with a quadrature bandpass characteristic. Through the integration of mixers in the AD converter, RF input signals in the range 0.3-1.6 GHz can be downconverted to a digital I and Q output stream at a bit rate of 128 MHz. The circuit is designed as a front-end for low power receivers with a 2 MHz wide IF bandwidth centered around 4 MHz. The converter, integrated in a 0.25 /spl mu/m CMOS technology, consumes 14 mW from a 2 V supply.