A Voltage Swing Robust Pseudo-Resistor Structure for Biomedical Front-end Amplifier

This paper proposes an improved pseudo-resistor structure with wide operation voltage. In bio-potential signal acquisition system, pseudo-resistors are always employed to realize very large RC time constant to suppress the input electrode DC offset voltage. With simple combination of two complementary back-to-back pseudo resistors, the resistance lifting across operating voltage is reduced. According to the simulation result with standard 0.18 μm CMOS process, the proposed pseudo-resistor provides robust resistance within 1.2 V voltage swing. A bandwidth tunable AC-coupled instrumentation amplifier which adopts a programmable resistor using the proposed pseudo-resistor is designed and simulated to verify the proposed structure.

I. Introduction

Typical bio-potential signal acquisition front-ends include the electrodes, instrumentation amplifiers and the following analog-to-digital converters. The electrode, actually, operates in an electrode-electrolyte interface environment. The chemical reaction at the interface and the electrode-body contact mismatch will result in an electrode DC offset (EDO), which may reach up to several hundred millivolts, varying slowly over time [1]. Therefore, the bio-potential readout circuit should exhibit high-pass filter (HPF) characteristic to attenuate the input EDO.