本論文著重在應用於植入式視覺輔具的多通道電刺激器以及阻抗量測電路。這個動機來自於色素性視網膜炎以及老年性黃斑部退化疾病導致感光細胞退化所引發的視覺障礙。正常的視網膜，透過感光細胞接收光刺激以產生神經訊號得到視覺；在感光細胞退化的視網膜上，則可利用視覺輔具透過視網膜或視覺皮質區上的電刺激，形成視覺感知。在此，我們設計了一個具有六十四通道刺激功能的電刺激器。 電刺激器必須透過電極作為介面才能對神經或肌肉進行電刺激。由於所植入的介面並非為平面，電極－組織介面阻抗可能會因接觸不良、電極大小與材質的差異，又或者電極本體受刺激電流、環境等因素而產生變化。基於以上因素，長期地觀測阻抗變化是必要的。因此，本論文中亦設計了一個使用時間數位轉換器之阻抗量測電路，觀察植入後電極－組織介面的阻抗變化狀況，這將有利於評估刺激成效以及刺激參數的調整。 This thesis aims to design a multi-channel electrical stimulator and impedance measurement system for implanted visual prosthesis. The motivation comes from retinitis pigmentosa (RP) and age-related macular degradation (AMD) both lead to photoreceptor degeneration and result in a significant visual deficit individual. In a healthy retina, the photoreceptors initiate a neural signal in response to light. In a retina with photoreceptor loss, a successful elicitation in visual perception will be possible by using electrical stimulation on retina or visual cortex by the visual prosthesis. In this paper, we design an electrical stimulator which is capable of 64-channel stimulation. The designed electrical stimulator stimulates nerves or muscles using electrodes as the interface. Due to the interface we implanted are not a flat surface, the electrode-tissue interface might have poor contact. Or the electrode size and material differences, electrode-self by stimulus current and environment factors, and so on. The impedance between electrode and tissue will be change. On account of these problems, a long term observation is required. Therefore, we designed an impedance measurement system with time-to-digital converter (TDC) to observe the status of electrode-tissue interface after implantation. It is useful for evaluating the effect on stimulation and adjustment of stimulus parameters.
