A Switchable-Order G$_{m}$-C Baseband Filter With Wide Digital Tuning for Configurable Radio Receivers

Abstract

A master/slave technique which allows digital tuning of a G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> -C filter's cut-off frequency is proposed. It relies on an accurate transconductance division technique, fixing the reference frequency independently from the filter cut-off frequency. The design of a digitally-tunable G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> -C switchable third/fifth- order Butterworth low-pass filter in a 0.13-mum 1.2-V CMOS process is also proposed. An extended tuning range (above 25:1) is obtained through the design of a linear very widely tunable transconductor. Measured results prove this chip to be compatible with the baseband part of direct-conversion cellular receivers, from GSM to W-CDMA, with a tuning accuracy better than 5% over the entire tuning range.