A 250MΩ Input Impedance a-IGZO Front-End for Biosignal Acquisition from Non-Contact Electrodes

This paper presents a high impedance, low noise, and low offset Analogue Front-End (AFE) designed to readout biosignals using non-contact electrodes. The circuit is fabricated in an amorphous InGaZnO (a-IGZO) technology. An autozeroing technique is used to reduce both 1/f noise and AFE offset while minimizing the charge required from the input, leading to a high input impedance. The AFE circuit makes use of two voltage buffers operated in a ping-pong configuration to ensure a continuous time operation. Measurement results reveal that, when autozeroing each 100μs, the AFE input impedance reaches 250MΩ at 50Hz, which is about 6x larger compared to the current state-of-the-art in large-area electronics. The Signal-to-Noise ratio estimated for non-contact electrodes with a 200MΩ series impedance remains above 20dB, while achieving a bandwidth of 1kHz, a power consumption of 0.22mW and an area per channel of 2.94mm
²
. Thanks to its versatility, the proposed AFE architecture in combination with the mechanical properties offered by the TFTs on foil, can be exploited to develop a new generation of wearable patches that are conformable, lightweight, and cost-effective. These devices could be employed in home health-monitoring applications to acquire biosignals such as sEMG (surface electromyography), while providing a great level of comfort to the patient.