Open Access OJAB A Low-Power CMOS Analog Front-End IC with Adjustable On-Chip Filters for Biosensors

Copyright © 2013 Donald Y. C. Lie et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper presents a low-power CMOS analog front-end (AFE) IC designed with a selectable on-chip dual AC/DC-coupled paths for bio-sensor applications. The DC-coupled path can be selected to sense a biosignal with useful DC information, and the AC-coupled path can be selected for sensing the AC content of the biosignal by attenuating the unwanted DC component. The AFE IC includes a DC-coupled instrumentation amplifier (INA), two variable-gain 1st-order low pass filters (LPF) with tunable cut-off frequencies, a fixed gain 2nd-order Sallen-Key high-pass filter (HPF) with tunable cut-off frequencies, a buffer and an 8-bit differential successive approximation register (SAR) ADC. The entire AFE channel is designed and fabricated in a proprietary 0.35-µm CMOS technology. Excluding an external buffer needed to properly drive the ADC, the measured AFE IC consumes only 2.37 µA/channel with an input referred noise of ~40 µVrms in [1 Hz, 1 kHz], and successfully displays proper ECG (electrocardiogram) and electrogram (EGM) waveforms for QRS peaks detection. We expect that the low-power dual-path design of this AFE IC can enable it to periodically record both the AC and the DC signals for proper sensing and calibration for various bio-sensing applica-tions