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.

[1] W. T. Liberson, H. J. Holmquest, D. Scot, and M. Dow, “Functional electrotherapy: stimulation of peroneal nerve synchronized with the swing phase of the gait of hemiplegic patients,” Archives of Physical Medicine and Rehabilitation, vol. 42, pp. 101-105, Feb. 1961.
[2] A. Kralj, T. Bajd, R. Turk, J. Krajnik, and H. Benko, “Gait restoration in paraplegic patients: a feasibility demonstration using multichannel surface electrode FES,” Journal of Rehabilitation R&D, vol. 20, pp. 3-20, Jul. 1983.
[3] C. W. Caldwell and J. B. Reswick, “A percutaneous wire electrode for chronic research use,” IEEE Transactions on Bio-Medical Engineering, vol. 22, no.5, pp. 429-432, Sep. 1975.
[4] D. R. McNeal, R. J. Nakai, P. Meadows, and W. Tu, “Open-loop control of the freely-swinging paralyzed leg,” IEEE Transactions on Bio-Medical Engineering, vol. 36, no. 9, pp.895-905, Sep. 1989.
[5] M. Mahadevappa, J. D. Weiland, D. Yanai, I Fine, R. J. Greenberg, and M. S. Humayun, “Perceptual thresholds and electrode impedance in three retinal prosthesis subjects,” IEEE Transactions on Neural Systems Rehabilitation Engineering, vol. 13, no. 2, pp. 201-206, Jun. 2005.
[6] A. P. Chu, K. Morris, R. J. Greenberg, and D. M. Zhou, “Stimulus induced pH changes in retinal implant,” IEEE Engineering in Medicine and Biology Society Conference, vol. 2, pp. 4160-4162, Sep. 2004.
[7] L. S. Y. Wong, S. Hossain, A. Ta, J. Edvinsson, D. H. Rivas, and H. Naas, “A very low-power CMOS mixed-signal IC for implantable pacemaker applications,” IEEE Journal of Solid-State Circuits, vol. 39, no. 12, pp. 2446-2456, Dec. 2004.
[8] J. Georgiou and C. Toumazou, “A 126-μW cochlear chip for a totally implantable system,” IEEE Journal of Solid-State Circuits, vol. 40, no. 2, pp. 430-443, Feb. 2005.
[9] S. K. Kelly and J. Wyatt, “A power-efficient voltage-based neural tissue stimulator with energy recovery,” IEEE Solid-State Circuits Conference, pp. 228-230, Feb. 2004.
[10] M. Ghovanloo, “Switched-capacitor based implantable low-power wireless microstimulating systems,” IEEE International Symposium on Circuits and Systems, pp. 2197-2200, May 2006.
[11] M. Sivaprakasam, W. Liu, G. Wang, J. D. Weiland, and M. S. Humayum, “Architecture tradeoffs in high-density microstimulators for retinal prosthesis,” IEEE Transactions on Circuits and Systems, Reg. Papers, vol. 52, no. 12, pp. 2629-2641, Dec. 2005.
[12] https://www.blindness.org
[13] http://webvision.med.utah.edu
[14] J. D. Weiland and M. S. Humayun, “Intraocular retinal prosthesis,” IEEE Engineering Medicine and Biology Magazine, vol. 25, pp. 60-66, Sep. 2006.
[15] J. D. Weiland, D. Yanai, M. Mahadevappa, R. Williamson, B. V. Mech, G. Y. Fujii, J. Little, R. J. Greenberg, E. de Juan Jr., and M. S. Humayun, “Electrical stimulation of retina in blind humans,” IEEE Engineering in Medicine and Biology Society Conference, vol. 3, pp. 2021-2022, Sep. 2003.
[16] P. Hossain, I. W. Seetho, A. C. Browning, and W. M. Amoaku, “Artificial means for restoring vision,” BMJ, vol. 330, pp. 30-33, Jan. 2005.
[17] K. Cha, K. W. Horch, R. A. Normann, and D. K. Boman, “Reading speed with a pixelized vision system,” Journal of the Optical Society of America. A, vol. 9, no. 5, pp. 673-677, May 1992.
[18] R. W Thompson, G. D. Barnett, M. S. Humayun, and G. Dagnelie, “Facial recognition using simulated prosthetic pixelized vision,” Investigative Ophthalmology and Visual Science, vol. 44, no. 11, pp. 5035-5042, Nov. 2003.
[19] M. Sivaprakasam, W. Liu, M. S. Humayun, and J. D. Weiland, “A variable range bi-phasic current stimulus driver circuitry for an implantable retinal prosthetic device,” IEEE Journal of Solid-State Circuits, vol. 40, no. 3, pp. 763-771, Mar. 2005.
[20] J. D. Weiland and M. S. Humayun, “A biomimetic retinal stimulating array: design considerations,” IEEE Engineering Medicine and Biology Magazine, vol. 24, no. 12, pp. 14-21, Sep. 2005.
[21] S. C. DeMarco, W. Liu, P. R. Singh, G. Lazzi, M. S. Humayun, and J. D. Weiland, “An arbitrary waveform stimulus circuit for visual prostheses using a low-area multibias DAC,” IEEE Journal of Solid-State Circuits, vol. 38, no. 10, pp. 1679-1690, Oct. 2003.
[22] B. Razavi, Design of Analog CMOS Integrated Circuits. New York: McGraw-Hill, 2001.
[23] D. A. Johns and K. Martin, Analog Integrated Circuit Design. New York: Wiley, 1997.
[24] W. Liu, K. Vichienchom, M. Clements, S. C. DeMarco, C. Hughes, E. McGucken, M. S. Humayun, E. Juan, J. D. Weiland, and R. Greenberg, “A neuro-stimulus chip with telemetry unit for retinal prosthetic device,” IEEE Journal of Solid-State Circuits, vol. 35, no. 10, pp. 1487-1497, Oct. 2000.
[25] A. B. Majji, M. S. Humayun, J. D. Weiland, S. Suzuki, S. A. D’Anna, and E. de Juan Jr., “Long-term histological and electrophysiological results of an inactive epiretinal electrode array implantation in dogs,” Investigative Ophthalmology and Visual Science, vol. 40, no. 9, pp. 2073-2081, Aug. 1999.
[26] A. S. Sedra and K. C. Smith, “Microelectronic circuits,” 5th ed. New York: Oxford, Aug. 2007.
[27] A. Harb and M. Sawan, “New low-power low-voltage high-CMRR CMOS instrumentation amplifier,” IEEE International Symposium on Circuits and Systems, vol. 6,pp. 97-100, May 1999.
[28] P. E. Allen and D. R. Holberg, CMOS Analog Circuit Design. New York: Oxford University Press, 2002.
[29] C. H. Kuo, S. L. Chen, and S. I. Liu, “Magnetic-field-to-digital converter using PWM and TDC techniques,” IEE Proceedings of Circuits, Devices and Systems, vol. 153, no. 3, pp. 247-252, Jun. 2006.
[30] P. Chen, S. L. Liu, and J. Wu, “A CMOS pulse-shrinking delay element for time interval measurement,” IEEE Transactions on Circuits and Systems, vol. 47, no. 9, pp. 954-958, Sep. 2000.
[31] S. Rajapandian, K. Shepard, P. Haxucha, and T. Karnik, “High-tension power delivery： Operating 0.18μm CMOS digital logic at 5.4V,” IEEE Solid-State Circuits Conference, vol. 1, pp. 298-599, Feb. 2005.
[32] C. T. Chiang and C. Y. Wu, “Implantable neuromorphic vision chips,” IET Electronics Letters, vol. 40, pp. 361-363, Mar. 2004.
[33] I. T. Mohammad, S. Pepe, and W. A. Gregory, “Implantable CMOS-based Stimulator/Reader Design for Retinal Prosthesis,” Conference on Microtechnology in Medicine and Biology, 3rd IEEE/EMBS, pp. 94-97, May. 2005.
[34] P. Nadeau and M. Sawan, “A flexible high voltage biphasic current-controlled stimulator,” IEEE International Symposium on Circuits and Systems, pp. 206-209, Nov. 2006.
[35] G. Lesbros and M. Sawan, “Multiparameters monitoring for long term in-vivo characterization of electrode-tissues contacts,” IEEE International Symposium on Circuits and Systems, pp. 25-28, Dec. 2006.
[36] A. Harb, Y. Hu, M. Sawan, A. Abdelkerim, and M. M. Elhilali, “Low-power CMOS interface for recording and processing very low amplitude signals,” Analog Integrated Circuits and Signal Processing, vol. 39, pp. 39-54, Mon. 2004.
[37] C. C. Wang, C. C. Huang, Y. C. Liu, V. Pikov, and D. Shmilovitz, “A mini-invasive multi-function biomedical pressure measurement system ASIC,” IEEE International Symposium on Circuits and Systems, pp. 2936-2939, May 2010.
[38] W. Qu, S. K. Islam, M. R. Mahfouz, M. R. Haider, G. To, and S. Mostafa, “Microcantilever array pressure measurement system for biomedical instrumentation,” IEEE Sensors Journal, vol. 10, no. 2, pp. 321-330, Feb. 2010.
[39] P. Napolitano, A. Moschitta, P. Carbone, “A survey on time interval measurement techniques and testing methods,” IEEE Transactions on Instrumentation and Measurement, pp. 181-186, May. 2010.