High-Input-Impedance Amplifiers Design for Dry-Electrode Biopotential Acquisition: A Review

Wearable health monitoring devices are becoming more and more popular due to their improved user comfort and long-term measurement capability. Dry-electrode based interfaces are often limited by skin-electrode impedance, leading to signal attenuation and CMRR degradation. In order to solve these problems, the analog front-end amplifier must be designed with ultra-high input impedance. To achieve this target while maintaining balanced overall performance, it is necessary to investigate both optimized amplifier architectures and input-impedance boosting techniques. This paper reviews the key limiting factors to realize an ultra-high input impedance biopotential amplifiers, dominated by on-chip and off-chip parasitic capacitance from both circuit and system perspectives. We summarize and compare a number of high-impedance biopotential amplifier architectures, as well as various impedance boosting techniques, as the guidelines to develop the next generation dry-electrode biopotential signal acquisition ASICs and systems.