A low-power 84-dB dynamic-range tunable Gm-C filter for bio-signal acquisition

Abstract

Abstract —A tunable Gm-C filter is presented for bio-signal acquisition application. It incorporates linear tunable trans-conductors utilizing MOSFETs biased in the triode region. Both the filter architecture and transconductor circuit design are optimized for good tuning, linearity and noise performance with low power consumption. The filter was fabricated in a 0.6 μ m BiCMOS process, occupying 0.17 mm 2 . Measurement results show a tuning range of cut-off frequency from 2.5 kHz to 10 kHz. At 5 kHz cut-off frequency, the filter achieves a dynamic range of 85 dB with 1% THD, and consumes 75.9 μ W from 3.3 V supply. Keywords— Gm-C filter, transconductor, bio-signal acquisition I. I NTRODUCTION Bio-potential signals provide vital information about the patient for disease diagnosis and health monitoring. Fig. 1 shows the block diagram of a typical bio-signal acquisition system. In the analog frontend, the ac-coupled low-noise amplifier (LNA) and the programmable-gain amplifier (PGA) provides gain to reduce noise contribution of subsequent blocks [1] [2]. They are followed by a low-pass filter to eliminate the out-of-band noise. In addition, this filter acts as anti-aliasing filter for the ADC backend. In biomedical applications, it is often desirable to have a filter with tunable cut-off frequency as the bio-signal can range from sub-Hz to a few kHz [3]. In a wearable or implantable system, low power consumption is imperative to extend the battery life and avoid heating of nearby tissue. Furthermore, as the bio-signal amplitude can range from several microvolts to tens of millivolts, high dynamic range (high linearity with low noise) is required to maintain fidelity of the acquired signal. All these requirements place challenges on the filter design. The filter function can be integrated in the LNA by adding load capacitors at the output of the amplifier [4]. This approach is not economic in terms of chip area because the LNA is normally placed in a feedback loop and has large trans-conductance (