IEEE Trans Biomed Circuits Syst. 2018 Dec;12(6):1267-1277. doi: 10.1109/TBCAS.2018.2883289. Epub 2018 Nov 26.
This paper presents a sub-mW ASIC for multimodal brain monitoring. The ASIC is co-integrated with electrode(s) and optodes (i.e., optical source and detector) as an active sensor to measure electroencephalography (EEG), bio-impedance (BioZ), and near-infrared spectroscopy (NIRS) on scalp. The target is to build a wearable EEG-NIRS headset for low-cost functional brain imaging. The proposed NIRS readout utilizes the near-infrared light to measure the pulse oximetry and blood oxygen saturation (SpO). While traditional photodiodes are supported, the readout also allows the use of silicon photomultipliers (SiPMs) as optical detectors. The SiPM improves optical sensitivity while significantly reducing the average power of two LEDs to 150 μW. On circuit level, a SAR-based calibration compensates maximum 40 μA current from ambient light, while digital DC-servo loops reduces the baseline static SiPM current up to 400 μA, leading to an overall dynamic range of 87 dB. The EEG readout exhibits 720 MΩ input impedance at 50 Hz. The BioZ readout has 3 mΩ/√(Hz) impedance sensitivity by employing dynamic circuit techniques. When EEG, BioZ, and NIRS are enabled at the same time, one ASIC consumes 665 μW including the power of LEDs.
本文提出了一种用于多模态脑监测的亚毫瓦 ASIC。该 ASIC 与电极和光探测器（即光源和探测器）共同集成作为有源传感器，以测量头皮上的脑电图（EEG）、生物阻抗（BioZ）和近红外光谱（NIRS）。目标是构建一个用于低成本功能脑成像的可穿戴 EEG-NIRS 耳机。所提出的 NIRS 读出利用近红外光来测量脉搏血氧饱和度（SpO）和血氧饱和度。虽然支持传统光电二极管，但读出也允许使用硅光电倍增管（SiPM）作为光学探测器。SiPM 提高了光学灵敏度，同时将两个 LED 的平均功率显著降低至 150μW。在电路级，基于 SAR 的校准补偿最大 40μA 的环境光电流，而数字 DC 伺服环路将 SiPM 的基线静态电流降低至 400μA，从而实现 87dB 的整体动态范围。EEG 读出在 50Hz 时具有 720MΩ 的输入阻抗。通过采用动态电路技术，BioZ 读出具有 3mΩ/√(Hz) 的阻抗灵敏度。当 EEG、BioZ 和 NIRS 同时启用时，一个 ASIC 消耗 665μW 的功率，包括 LED 的功率。
