Research And Design Of Preamplifier In Ultra Low Power Sensor Interface

A pre-amplifier, proposed in this paper, which is used in ultralow power sensor interface circuits and is mainly applied to monitor biopotential of human body such as Electrocardiography (ECG) and Electroencephalography (EEG) employs fully differential capacitor-coupled chopper-stabilized structure and achieves ultralow power, ultralow noise and high common mode rejection ratio.This work complete the whole design flow including specification determination, system architecture analysis and design, module optimization, tape out and chip test. The major contributions and innovations are as following:1. Determine the specification of pre-amplifier according to the signal characteristic of human body biopotential (ECG/EEG) and different interferences;2. Propose the structure of fully differential capacitor-coupled chopper-stabilized amplifier adapting to the application environment and design specifications, improve DC offset cancellation(DCOC) capability, power and noise performance;3. Analysis and optimization design for the power, noise and offset of major amplifier, determine optimization methods under power limit;4. Analysis and design of DCOC loop which achieves high DC offset cancellation, solve the design problem of filter with large time constant and leakage of gate;5. Design second order Gm-C low pass filter which can filter out ripples and spikes, solve the conflict between implementation of large time constant and chip area;6. Propose a digital ripple reduction loop which employs digital method to reduce output ripples and can effectively save power, area and lower noise.The design which is fabricated in0.13-μm SMIC CMOS process occupies0.285mm2with a1.2V supply. Experimental results yield a1.96μA current consumption, a40dB gain with bandwidth from0.17Hz to189Hz and a2.2μVrms in-band input referred integrated noise voltage. The common mode rejection ratio at50Hz is92dB while the power supply rejection ratio is100dB. DCOC capacity is±60mV. This work achieves design specifications completely and demonstrates the ECG signal monitoring.