NeuraPlex - High-density fully-immersible subcortical neural data digitizer based on time-division multiplexing

该研究项目的目标是开发和实现第一个空间分辨率低于50µm的高密度全浸入式CMOS神经探针。目前的技术水平一方面受到传统的有源神经探针的限制，这些探针的电极间距小，但包含一个大的底座和大量的连接导线。另一方面，它提供了一种完全浸入式的CMOS神经探针，具有最小的底座，以大电极间距为代价，需要更少的连接。新探头通过实施针对该应用量身定制的优化信号处理链，推进了最先进的状态。因此，既不需要笨重的连接器，也不需要将复杂的电路集成到底座中，这反过来又产生了具有小电极间距和从尖端到底座均匀宽度的纤细探头。因此，可以节省大量的硅面积和成本。此外，探头可以完全浸入脑组织，从而实现高信噪比、大带宽和适当空间分辨率的单神经元信号的皮质下记录。该目标将通过将“数字”多电极阵列集成到手柄中来实现。然而，由于手柄上每个通道的可用面积有限，多个电极将需要共享一个模数转换器（ADC）。到目前为止，时分复用需要前置放大器和显式抗混叠滤波器来实现，从而导致大面积。为了在手柄的有限面积上实现相同的效果，同时避免组织的过度功耗和温度升高，需要开发专用的ADC架构。该ADC必须满足高密度全浸入式CMOS神经探针所定义的最小面积、最小功耗和超低噪声等规格。因此，将对连续时间增量Delta-Sigma adc的架构进行基础研究。其固有的抗混叠滤波器以及在多路传感器系统中的适用性使其成为神经记录系统的完美候选人。由此产生的高密度神经探针具有同时监测数百个神经元的单个活动的能力，将为神经科学家提供在更深区域进行大脑活动研究和获得对神经网络的理解的新机会。此外，结合神经刺激器，它可以用来实现闭环系统，从而有助于追求缓解神经和心理疾病的症状。由于对超低功耗、高分辨率、多通道adc的需求不断增长，对连续时间增量Delta-Sigma adc架构的基础研究结果对仪器仪表和测量或物联网等其他应用具有重要影响。

The objective of this research project is to develop and implement the first high-density fully-immersible CMOS neural probe with a spatial resolution lower than 50 µm. The state of the art is limited on one hand by conventional active neural-probes with a small electrode pitch but encompassing a large base and a high number of connecting wires. On the other hand, it offers a fully immersible CMOS neural probe featuring a minimal base and requiring fewer connections at the cost of a large electrode pitch. The new probe advances the state of the art by implementing an optimized signal processing chain tailored to this application. Hence, neither a bulky connector is required nor elaborate circuits need to be integrated into the base, which in turn yields a slim probe with a small electrode pitch and a uniform width from tip to base. Thus, substantial silicon area and costs can be saved. In addition, the probe can be fully immersed into the brain tissue whereby subcortical recording of single-neuron signals with a high signal-to-noise ratio, a large bandwidth and an appropriate spatial resolution becomes feasible.The objective will be met by integrating a “digital” multi-electrode-array into the shank. However, since the available area per channel on the shank is limited, multiple electrodes will need to share one analog-to-digital converter (ADC). Time-division multiplexing as performed up to now requires preamplifiers and an explicit anti-aliasing filter to be implemented on the base leading to a large area. To achieve the same on the limited area of the shank and still avoid excessive power consumption and temperature increase of the tissue, a dedicated ADC architecture needs to be developed. This ADC must meet, amongst others, the specifications of smallest-area, minimal-power consumption, and ultra-low-noise as defined by the high-density fully immersible CMOS neural probe. Fundamental research will thus be performed on architectures for continuous-time, incremental Delta-Sigma ADCs. Their intrinsic anti-aliasing filter as well as their applicability in multiplexed sensor systems make them the perfect candidate for neural recording systems.The resulting high-density neural probe with its capability to simultaneously monitor the single activity of hundreds of neurons will provide neuroscientists with new opportunities for performing research on brain activity in deeper regions and for gaining understanding of neural networks. Moreover, combined with a neural stimulator, it can be used to implement a closed-loop system and thus contribute to the pursuit of relieving the symptoms of neurological and psychological diseases.Due to the ever-increasing demand for ultra-low-power, high-resolution, multi-channel ADCs, the outcome of the fundamental research on architectures for continuous-time incremental Delta-Sigma ADCs are of high impact for other applications such as instrumentation and measurement or the Internet of Things.