IEEE Trans Biomed Circuits Syst. 2024 Oct;18(5):1079-1088. doi: 10.1109/TBCAS.2024.3374891. Epub 2024 Sep 26.
Non-invasive, closed-loop brain modulation offers an accessible and cost-effective means of evaluating and modulating one's mental and physical well-being, such as Parkinson's disease, epilepsy, and sleep disorders. However, wearable EEG systems pose significant challenges for the analog front-end (AFE) circuits in view of µV-level EEG signals of interest, multiple sources of interference, and ill-defined skin contact. This paper presents a direct-digitization AFE tailored for dry-electrode scalp EEG recording, characterized by wide input dynamic range (DR) and high input impedance. The AFE utilizes a second-order 5-bit delta-delta sigma (Δ-ΔΣ) ADC to shape DC electrode offset (DEO) and low-frequency disturbances while retaining high accuracy. A non-inverting pseudo-differential instrumentation amplifier (IA) embedded in the ADC ensures high input impedance (Z) and common-mode rejection ratio (CMRR). Fabricated in a standard 0.18-μm CMOS process, the AFE delivers 700-mV input signal range, 95.3-dB DR, 87-dB SNDR, and 800-MΩ input impedance at 50 Hz while consuming 88.4µW from a 1.2 V supply. The benefits of high DR and high input impedance have been validated by dry-electrode EEG measurement.
非侵入式、闭环脑调制为评估和调节人们的身心健康提供了一种便捷且具有成本效益的手段，例如帕金森病、癫痫和睡眠障碍。然而，可穿戴 EEG 系统对模拟前端 (AFE) 电路提出了重大挑战，因为它需要处理感兴趣的微伏级 EEG 信号、多种干扰源和不明确的皮肤接触。本文提出了一种针对干电极头皮 EEG 记录的直接数字化 AFE，其特点是宽输入动态范围 (DR) 和高输入阻抗。该 AFE 利用二阶 5 位 delta-delta sigma (Δ-ΔΣ) ADC 来塑造直流电极偏移 (DEO) 和低频干扰，同时保持高精度。嵌入 ADC 中的反相伪差分仪表放大器 (IA) 确保了高输入阻抗 (Z) 和共模抑制比 (CMRR)。该 AFE 采用标准的 0.18-μm CMOS 工艺制造，在 50 Hz 时可提供 700 mV 的输入信号范围、95.3 dB 的 DR、87 dB 的 SNDR 和 800 MΩ 的输入阻抗，同时从 1.2 V 电源消耗 88.4µW 的功率。高 DR 和高输入阻抗的优势已通过干电极 EEG 测量得到验证。
