Wide digitally tunable lowpass filter for biomedical and wireless applications

Abstract

A fully differential Gm-C lowpass filter for wireless and biomedical applications is introduced in this Letter. The proposed filter is based on a highly linear CMOS digital programmable operational transconductance amplifier (DPOTA).The filter consists of a parallel connection of three fourth-order Butterworth sections. Each section is optimised for a specific band of frequencies which can be tuned digitally. Switching between the different sections is achieved by controlling the corresponding DPOTAs' transconductance values, hence, this filter design eliminates the need for switches. Simulation results for a 90 nm CMOS technology are given. The third-order harmonic distortion (HD3) of the DPOTA remains below -60 dB up to 0.5 V differential input voltage at 1.2 V supply voltage. The proposed filter exhibits a wide cutoff frequency tuning range, from 100 Hz to 12 MHz, thus it covers many biomedical and wireless communication standards.