A 2.55 NEF 76 dB CMRR DC-Coupled Fully Differential Difference Amplifier Based Analog Front End for Wearable Biomedical Sensors.

High input impedance, low noise, high common mode rejection ratio (CMRR), and ultralow power are the most important performance indicators in the design of analog front end (AFE) for wearable biomedical sensors. This paper presents a fully differential difference amplifier based AFE that employs dc-coupled input stage to increase the input impedance and improve CMRR. A parasitic capacitor reuse technique is proposed to improve the noise/area efficiency and CMRR. An on-body dc bias scheme is introduced to deal with the input dc offset. Implemented in 0.35 μm CMOS process with an area of 0.405 mm, the proposed AFE consumes 0.9 μW at 1.8 V and shows excellent noise effective factor of 2.55, and CMRR of 76 dB. Experiment shows the proposed AFE not only picks up clean ECG signal with electrodes placed as close as 2 cm under both resting and walking conditions, but also obtain the distinct α-wave after eye blink from EEG recording.