低噪声、低纹波头皮脑电信号采集的前端电路-《中国医学物理学杂志》

文章信息/Info

Title:: A low noise and low ripple front-end circuit for collecting scalp EEG signals

Author(s):: LI Hao; WANG Yuhan; XUE Kailong; YUAN Yi; LI Xiaolong; Department of Electronics and Information, Jiangsu University of Science and Technology, Zhenjiang 212003, China

Keywords:: Keywords: scalp EEG acquisition preamplifier chopping technology ripple rejection circuit programmable-gain amplifier

摘要:: 基于SMIC 0.18 μm CMOS工艺设计了一种由前置放大器、纹波抑制电路、增益可编程放大器和外置低通滤波器组成的低噪声头皮脑电信号采集前端电路。其中前置放大器采用斩波技术来降低低频噪声和失调电压，其结构为电容耦合的斩波稳定放大器，其有源放大部分由折叠式共源共栅级和共源级构成的两级全差分放大器构成，以获得较高的开环增益；同时在前置放大器后引入了阻容耦合电路来抑制在斩波频率处产生的纹波。可编程增益放大器采用可调电容阵列构成的电容负反馈放大器以实现增益逐级可调。Spectre后仿真结果表明，前置放大器的增益为40 dB，共模抑制比可达131 dB，电源抑制比90 dB，输入等效噪声772 nV/sqrt(Hz)@100 Hz；可编程增益放大器的增益分别为12、20、25 dB；低通滤波器的截止频率为1 kHz；纹波抑制电路对在斩波频率处的纹波具有400倍的抑制效果。该前端电路的总增益为40~65 dB，通频带为1 Hz~1 kHz。

Abstract:: Abstract: Based on the SMIC 0.18 μm CMOS process, a front-end circuit for low noise scalp EEG acquisition, which composes preamplifier, ripple rejection circuit, programmable-gain amplifier (PGA) and low-pass filter, is proposed. The preamplifier employs the chopper technology to reduce the low-frequency noise and offset voltage. It is a capacitive-coupled chopper-stabilized amplifier, and its active amplification is a two-stage amplifier consisting of a differential folded-cascode stage and a differential common source stage in order to achieve a higher open-loop gain. At the output of the preamplifier, a parallel resistor-capacitor circuit is introduced to suppress the ripple at the chopping frequency. The PGA is a capacitive negative-feedback amplifier combined with an adjustable array, aiming to realize that the gain can be adjusted step by step. The results of Spectre post-simulation show that the preamplifier can achieve a voltage gain of 40 dB, a common mode rejection ratio (CMRR) of 131 dB, a power supply rejection ratio (PSRR) of 90 dB, and an equivalent input noise of 772 nV/sqrt (Hz) @ 100 Hz. The gain of the PGA can be set as 10 dB, 20 dB, 25 dB, respectively. The cut-off frequency of the low-pass filter is 1 kHz. The ripple at the chopping frequency can be suppressed 400-fold. As a result, the total gain of the front-end circuit is variable from 40 dB to 65 dB, and the passband is 1 Hz-1 kHz.