Design of a programmable and low-frequency filter for biomedical signal sensing applications

Abstract

A programmable low-frequency filter for biomedical signal sensing application is presented here based on the principle of fifth-order Bessel transconductance capacitor (Gm-C) ladder filter. Current division and current cancellation techniques are used to achieve ultra-low Gm for operation transconductance amplifier (OTA) design. Active inductor is designed through a gyrator structure composed of an OTA and a capacitor. In order to achieve tunable cutoff frequency for the filter, constant Gm and variable capacitor structures are utilized in the design. The cutoff frequency can thus be adjusted as 35Hz, 150Hz and 250Hz through two digital control bits CTRSA and CTRSB. Gm is also adjustable to compensate frequency drift caused by the process and temperature variation. The filter was designed with 0.18μm 1P6M CMOS technology and achieves a THD of 61.2dB and consumes 12.38μW under 1.8V supply voltage.