Performance summary.

This paper presents a low-power, second-order composite source-follower-based filter architecture optimized for biomedical signal processing, particularly ECG and EEG applications. Source-follower-based filters are recommended in the literature for high-frequency applications due to their lower power consumption when compared to filters with alternative topologies. However, they are not suitable for biomedical applications requiring low cutoff frequencies as they are designed to operate in the saturation region. The major contribution in this work are the filter is made to operate in the weak inversion zone to reduce the area needed for the capacitor and the amount of power dissipated. Process variation is one of the major issues in the weak inversion regime. To overcome this, a unique method of compensating against fluctuations in process, voltage, and temperature is put forth based on magnitude comparison is another contribution. Key findings from post-layout simulations and experimental measurements demonstrate that the filter achieves a tunable cutoff frequency range of 0.5 Hz to 150 Hz, with a total power dissipation of only 6nW at 150 Hz. The design occupies a compact silicon area of 0.065 mm2 and offers a dynamic range of 75 dB. The measured results indicate that for a 300 mVpp signal swing, the top bound on THD is -40 dB. The filter’s robustness against process, voltage, and temperature variations is validated through on-chip tuning using a current steering DAC, ensuring stable performance across different operating conditions. These results make the proposed filter a promising candidate for low-power biomedical devices. The recommended filter is developed and implemented using UMC-0.18μm CMOS technology with a 1.0V supply, and the IC is tapped out using an MPW run of Euro practice IC services.

本文提出了一种基于源跟随器（source-follower）的低功耗二阶复合滤波器架构，专为生物医学信号处理场景优化，尤其适用于心电图（ECG）与脑电图（EEG）应用。现有研究文献表明，相较于其他拓扑结构的滤波器，基于源跟随器的滤波器因功耗更低，被推荐用于高频应用场景。但这类滤波器通常设计为工作于饱和区，无法满足对截止频率要求较低的生物医学应用需求。本研究的核心贡献在于两点：其一，将滤波器的工作区域调整至弱反型区，以缩减电容所需面积并降低功耗；其二，针对弱反型区中工艺偏差这一核心挑战，提出了一种基于幅值比较的工艺、电压与温度波动补偿方案。布局后仿真与实验测试的关键结果显示，该滤波器的可调截止频率范围为0.5 Hz至150 Hz，在150 Hz工况下总功耗仅为6nW。该设计的硅片面积仅为0.065 mm²，动态范围可达75 dB。测试结果表明，当信号摆幅为300 mVpp时，总谐波失真（THD）的上限为-40 dB。通过电流舵数模转换器（current steering DAC）实现片上调试，验证了该滤波器对工艺、电压与温度变化的鲁棒性，可确保其在不同工作条件下均能保持稳定性能。上述结果表明，本文提出的滤波器是低功耗生物医学设备的极具潜力的候选方案。该滤波器采用UMC 0.18μm互补金属氧化物半导体（CMOS）工艺开发实现，电源电压为1.0V，芯片通过欧洲实践IC服务（Euro Practice IC Services）的多项目晶圆（MPW）流片完成。