隨著時代與科技的發展，生醫電子越來越受到人們的重視，其中功能性電刺激被研究出可以用來治療許多身體的殘疾或是神經方面疾病，而仰賴半導體技術的提升，這一方面的醫療器材得以積體化成植入式裝置來取代受損部位或隨時監控並治療神經方面疾病。深層腦部刺激就是其中一種用來以電刺激來抑制腦部不正常放電的治療方式，可以用來治療帕金森氏症或癲癇等腦神經相關疾病。
而近年來，在電刺激的刺激波形的研究方面，有別於以往常見的方波波形刺激，許多團隊開始研究該種刺激的效益並與非方波式刺激的比較，許多研究成果都得出或提到指數下降式電流刺激在能成功誘發神經動作電位的情況下能有較好的能量效益表現。

本論文提出一個可應用在深層腦部刺激的高能量效益指數電流刺激電路，使用1V供給電壓並可輸出最大300uA指數電流至20kohm等校阻抗的電極。有別於常見之固定高電壓供給輸出電流路徑方式，本研究在第一版中提出一個回授架構使得升壓電路的輸出電壓會隨著輸出的刺激電流大小調整以減少在輸出電流非峰值時所浪費的功耗而達到高能量效益。而在第二版本設計中提出了可以操作在此種變動高電壓下的耐高壓開關電路及其控制、偏壓電路。而在實際情形，電極的阻抗可能並非理想值，所以如何因應該阻抗變化以避免輸出電流失真或能量效益不理想的問題也在本研究的第二版本設計中考量並提出解決方式。所提出的電路架構皆以標準TSMC 0.18um CMOS製程來模擬並實現，而電路方面也設計了一些方式來使標準的電晶體可以承受高壓，而在第二版本的設計中可以完整的輸出雙相指數電流刺激，並且降低40%的能量消耗。

關鍵字：、、

With the development of technology, Bio-medical Electrics has drawn more attention then before. Researches had shown that Functional electrical stimulation(FES) can be used to cure or replace function loss of human body and can even treat some neuron-related diseases. And thanks to the improvement of semi-conductor technology, these bio-medical devices can be integrated into small implant devices, which can replace damaged function on human body in daily life or detect and cure neuron-related problems whenever necessary. In recent years, many research groups has started to compare conventional rectangular stimuli with non-rectangular ones, and most groups has mentioned or concluded the high energy-efficiency of exponentially deceasing current stimuli.

A high energy-efficiency current stimulator that can be applied to deep brain stimulation(DBS) has been proposed in this study. A maximum 300uA output stimulation can be generated to electrode of 20kohm equivalent impedance with 1V supply voltage. In order to reduce energy consumption while delivering stimulation, exponential current pulses are used due to their higher energy-efficiency when inducing action potential on tissue than conventional rectangular pulses. However, conventional exponential stimulators use a fixed high voltage source to drive the output stimulation path, this causes energy waste while exponential stimulation is not at its peak current.Therefore, a technique is proposed to make the output high voltage tracing the output stimulation current to reach high energy-efficiency. A high voltage tolerant switch array is also proposed to sustain the mentioned varying high voltage. The proposed work is simulated and fabricated using standard TSMC 0.18 um process and the circuit is designed with consideration of high voltage issue on transistors. The second proposed design is measured to have 40\% of energy consumption reduction and can generate a full biphasic exponential pulse.

[1] 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.
[2] S. K. Kelly and J. Wyatt, “A power-efficient voltage-based neural tissue stimulator
with energy recovery,” in 2004 IEEE International Solid-State Circuits
Conference (IEEE Cat. No.04CH37519), Feb 2004, pp. 228–524 Vol.1.
[3] M. Sivaprakasam, W. Liu, G. Wang, M. Zhou, J. D. Weiland, and M. S.
Humayun, “Architecture tradeoffs in high density microstimulators for retinal
prosthesis,” in Conference Proceedings. 2nd International IEEE EMBS
Conference on Neural Engineering, 2005., March 2005, pp. 466–469.
[4] I. Williams and T. G. Constandinou, “An energy-efficient, dynamic voltage
scaling neural stimulator for a proprioceptive prosthesis,” IEEE Transactions
on Biomedical Circuits and Systems, vol. 7, no. 2, pp. 129–139, April 2013.
[5] T. G. Constandinou, J. Georgiou, and C. Toumazou, “A partial-currentsteering
biphasic stimulation driver for vestibular prostheses,” IEEE Transactions
on Biomedical Circuits and Systems, vol. 2, no. 2, pp. 106–113, June
2008.
[6] C. Y. Lin, W. L. Chen, and M. D. Ker, “Implantable stimulator for epileptic
seizure suppression with loading impedance adaptability,” IEEE Transactions
on Biomedical Circuits and Systems, vol. 7, no. 2, pp. 196–203, April 2013.
[7] M. Monge, M. Raj, M. H. Nazari, H. C. Chang, Y. Zhao, J. D. Weiland, M. S.
Humayun, Y. C. Tai, and A. Emami, “A fully intraocular high-density selfcalibrating
epiretinal prosthesis,” IEEE Transactions on Biomedical Circuits
and Systems, vol. 7, no. 6, pp. 747–760, Dec 2013.
[8] E. Noorsal, K. Sooksood, H. Xu, R. Hornig, J. Becker, and M. Ortmanns, “A
neural stimulator frontend with high-voltage compliance and programmable
pulse shape for epiretinal implants,” IEEE Journal of Solid-State Circuits,
vol. 47, no. 1, pp. 244–256, Jan 2012.
[9] S. Jezernik and M. Morari, “Energy-optimal electrical excitation of nerve
fibers,” IEEE Transactions on Biomedical Engineering, vol. 52, no. 4, pp.
740–743, April 2005.
[10] M. Sahin and Y. Tie., “Non-rectangular waveforms for neural stimulation
with practical electrodes.” in Journal of neural engineering, May 2007, pp.
227–233.
[11] A. Wongsarnpigoon, J. P. Woock, and W. M. Grill, “Efficiency analysis of
waveform shape for electrical excitation of nerve fibers,” IEEE Transactions
on Neural Systems and Rehabilitation Engineering, vol. 18, no. 3, pp. 319–328,
June 2010.
[12] Foutz, TJ, and C. McIntyrem., “Evaluation of novel stimulus waveforms for
deep brain stimulation.” in Journal of neural engineering, Dec 2010, p. 066008.
[13] S. Ethier and M. Sawan, “Exponential current pulse generation for efficient
very high-impedance multisite stimulation,” IEEE Transactions on Biomedical
Circuits and Systems, vol. 5, no. 1, pp. 30–38, Feb 2011.
[14] M. H. Maghami, A. M. Sodagar, and M. Sawan, “Biphasic, energy-efficient,
current-controlled stimulation back-end for retinal visual prosthesis,” in 2014
IEEE International Symposium on Circuits and Systems (ISCAS), June 2014,
pp. 241–244.
[15] B. Fotouhi, “All-mos voltage-to-current converter,” IEEE Journal of Solid-
State Circuits, vol. 36, no. 1, pp. 147–151, Jan 2001.
[16] M. Quarantelli, M. Poles, M. Pasotti, and P. Rolandi, “A high compliance
cmos current source for low voltage applications,” in Circuits and Systems,
2003. ISCAS ’03. Proceedings of the 2003 International Symposium on, vol. 1,
May 2003, pp. I–425–I–428 vol.1.
[17] M. Ghovanloo and K. Najafi, “A compact large voltage-compliance high
output-impedance programmable current source for implantable microstimulators,”
IEEE Transactions on Biomedical Engineering, vol. 52, no. 1, pp.
97–105, Jan 2005.
[18] M.-D. Ker, S.-L. Chen, and C.-S. Tsai, “Design of charge pump circuit with
consideration of gate-oxide reliability in low-voltage cmos processes,” IEEE
Journal of Solid-State Circuits, vol. 41, no. 5, pp. 1100–1107, May 2006.
[19] M. K. Hati and T. K. Bhattacharyya, “A power efficient and constant-gm
1.8 v cmos operational transconductance amplifier with rail-to-rail input and
output ranges for charge pump in phase-locked loop,” in 2012 International
Conference on Devices, Circuits and Systems (ICDCS), March 2012, pp. 38–43.
[20] C. Y. Lin, Y. J. Li, and M. D. Ker, “High-voltage-tolerant stimulator with
adaptive loading consideration for electronic epilepsy prosthetic soc in a 0.18-
m cmos process,” in 10th IEEE International NEWCAS Conference, June
2012, pp. 125–128.
[21] J. Liu, L. Ye, Z. Deng, J. Zhao, and H. Liao, “A 1.8v to 10v cmos level
shifter for rfid transponders,” in 2010 10th IEEE International Conference
on Solid-State and Integrated Circuit Technology, Nov 2010, pp. 491–493.
[22] V. Valente, A. Demosthenous, and R. Bayford, “A tripolar current-steering
stimulator asic for field shaping in deep brain stimulation,” IEEE Transactions
on Biomedical Circuits and Systems, vol. 6, no. 3, pp. 197–207, June 2012.
[23] M. E. Halpern* and J. Fallon, “Current waveforms for neural stimulationcharge
delivery with reduced maximum electrode voltage,” IEEE Transactions on Biomedical Engineering, vol. 57, no. 9, pp. 2304–2312, Sept 2010.
[24] 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, March 2005.
[25] X. Liu, A. Demosthenous, and N. Donaldson, “An integrated implantable
stimulator that is fail-safe without off-chip blocking-capacitors,” IEEE Transactions
on Biomedical Circuits and Systems, vol. 2, no. 3, pp. 231–244, Sept
2008.
[26] K. Khare, N. Khare, and P. K. Sethiya, “Analysis of low voltage rail-torail
cmos operational amplifier design,” in 2008 International Conference on
Electronic Design, Dec 2008, pp. 1–4.
[27] B. Lee and T. Higman, “1.2v constant-gm rail-to-rail cmos op-amp input stage
with new overlapped transition regions technique for ecg amplifier,” in 2013
35th Annual International Conference of the IEEE Engineering in Medicine
and Biology Society (EMBC), July 2013, pp. 3451–3454.
[28] P. S. Motta and J. W. Judy, “Multielectrode microprobes for deep-brain
stimulation fabricated with a customizable 3-d electroplating process,” IEEE
Transactions on Biomedical Engineering, vol. 52, no. 5, pp. 923–933, May
2005.
[29] J.-T. Wu and K.-L. Chang, “Mos charge pumps for low-voltage operation,”
IEEE Journal of Solid-State Circuits, vol. 33, no. 4, pp. 592–597, Apr 1998.
[30] D. McCreery, A. Lossinsky, V. Pikov, and X. Liu, “Microelectrode array for
chronic deep-brain microstimulation and recording,” IEEE Transactions on
Biomedical Engineering, vol. 53, no. 4, pp. 726–737, April 2006.
[31] H. M. Lee, H. Park, and M. Ghovanloo, “A power-efficient wireless system
with adaptive supply control for deep brain stimulation,” IEEE Journal of
Solid-State Circuits, vol. 48, no. 9, pp. 2203–2216, Sept 2013.
[32] R. Rieger, A. Demosthenous, and J. Taylor, “A 230-nw 10-s time constant
cmos integrator for an adaptive nerve signal amplifier,” IEEE Journal of
Solid-State Circuits, vol. 39, no. 11, pp. 1968–1975, Nov 2004.
[33] S. Ethier, M. Sawan, and M. El-Gamal, “A novel energy-efficient stimuli
generator for very-high impedance intracortical microstimulation,” in Proceedings
of 2010 IEEE International Symposium on Circuits and Systems,
May 2010, pp. 961–964.
[34] B. Tahayori and S. Dokos, “Optimal stimulus current waveshape for a
hodgkin-huxley model neuron,” in 2012 Annual International Conference of
the IEEE Engineering in Medicine and Biology Society, Aug 2012, pp. 4627–
4630.
[35] ——, “Optimal stimulus profiles for neuroprosthetic devices: Monophasic
versus biphasic stimulation,” in 2013 35th Annual International Conference
of the IEEE Engineering in Medicine and Biology Society (EMBC), July 2013,
pp. 5978–5981.
[36] L. F. New, Z. A. bin Abdul Aziz, and M. F. Leong, “A low ripple cmos charge
pump for low-voltage application,” in 2012 4th International Conference on
Intelligent and Advanced Systems (ICIAS2012), vol. 2, June 2012, pp. 784–
789.
[37] M. H. Huang, P. C. Fan, and K. H. Chen, “Low-ripple and dual-phase
charge pump circuit regulated by switched-capacitor-based bandgap reference,”
IEEE Transactions on Power Electronics, vol. 24, no. 5, pp. 1161–1172,
May 2009.
[38] A. Homayoun and B. Razavi, “On the stability of charge-pump phase-locked
loops,” IEEE Transactions on Circuits and Systems I: Regular Papers, vol. 63,
no. 6, pp. 741–750, June 2016.
[39] C. Hangmann, C. Hedayat, and U. Hilleringmann, “Stability analysis of
a charge pump phase-locked loop using autonomous difference equations,”
IEEE Transactions on Circuits and Systems I: Regular Papers, vol. 61, no. 9,
pp. 2569–2577, Sept 2014.
[40] P. K. Hanumolu, M. Brownlee, K. Mayaram, and U.-K. Moon, “Analysis of
charge-pump phase-locked loops,” IEEE Transactions on Circuits and Systems
I: Regular Papers, vol. 51, no. 9, pp. 1665–1674, Sept 2004.