IEEE Trans Biomed Circuits Syst. 2022 Aug;16(4):557-569. doi: 10.1109/TBCAS.2022.3198911. Epub 2022 Oct 12.
The design, development, and experimental validation of an inductively-powered four-channel optical neuro-stimulator system on a chip (SoC) with on-chip neural recording, temperature monitoring, signal processing, and bidirectional wireless data communication are presented. A biologically-inspired optical stimulation approach is employed that extends the limitations on the stimulation pulse-width and frequency (i.e., enabling wirelessly-powered optical stimulation at very low frequencies (e.g., 10 Hz)) while significantly reducing the required on-device storage capacitor size. The biological efficacy of the proposed approach is validated and compared with conventional stimulation through in vitro experiments. The stimulator's energy efficiency is enhanced by employing a high-gain (850 A/A) current amplifier/driver in each channel that steers up to 10 mA into the optical source with an excellent linearity ( 0.5LSB), while 1) yielding the lowest-in-literature required voltage headroom, and 2) being insensitive to large (up to 12%) supply voltage drops, which is ideal for battery-less implantable devices. Additionally, to maximize the percentage of the generated optical power that reaches the targeted cells (thus, further energy efficiency enhancement), inkjet printing is utilized to fabricate custom-designed optical μlenses that are placed directly on top of the silicon SoC to enhance the generated light's directivity by > 30×. An electrophysiological recording channel for real-time monitoring of the stimulation efficacy and a high-precision (0.1 C resolution) temperature readout circuit for shutting off stimulation upon detection of an unsafe temperature increase are also integrated on the chip. Additionally, the SoC hosts an ASK receiver and an LSK transmitter for downlink and uplink wireless data communication, respectively. The SoC is fabricated in a standard 130 nm CMOS process and occupies 6 mm . Measurement results for different sensory and communication blocks are presented, as well as in vitro experimental validation results showing simultaneous optical stimulation, electrical recording, and calcium imaging.
本文提出了一种基于片上系统（SoC）的感应供电四通道光神经刺激器系统的设计、开发和实验验证，该系统具有片上神经记录、温度监测、信号处理和双向无线数据通信功能。采用了一种受生物启发的光刺激方法，该方法扩展了刺激脉冲宽度和频率的限制（即，能够以非常低的频率（例如 10 Hz）进行无线供电的光刺激），同时显著减小了所需的片上存储电容器的尺寸。通过体外实验验证和比较了所提出方法的生物功效与传统刺激方法。通过在每个通道中采用高增益（850 A/A）电流放大器/驱动器，将高达 10 mA 的电流引导到光学源，实现了优异的线性度（0.5LSB），同时 1）产生文献中要求的最低电压裕量，2）对大的（高达 12%）电源电压下降不敏感，这对于无电池植入式设备非常理想，从而提高了刺激器的能量效率。此外，为了最大限度地提高到达目标细胞的光功率百分比（从而进一步提高能量效率），采用喷墨印刷技术制造了定制设计的光学 μlenses，将其直接放置在硅 SoC 上方，以将生成光的指向性提高 >30 倍。该系统还集成了一个电生理记录通道，用于实时监测刺激效果，以及一个高精度（0.1 C 分辨率）温度读取电路，用于在检测到不安全的温度升高时关闭刺激。此外，SoC 还集成了 ASK 接收器和 LSK 发射器，用于下行链路和上行链路无线数据通信。SoC 采用标准的 130nm CMOS 工艺制造，占用 6mm 。本文还介绍了不同传感和通信模块的测量结果，以及体外实验验证结果，包括同时进行的光刺激、电记录和钙成像。
