本論文提出一個多差動輸出差動輸入轉導電容濾波器(Multiple-Output Differential-Input Operational Transconductance Amplifier-C Filter, MODI OTA-C Filter），主要應用於近身端心電訊號擷取裝置。為減少濾波器係數對於製程、電壓以及溫度變異之靈敏度以及訊號失真的影響，濾波器組態採用五階巴特沃茲低通濾波器。為滿足生醫系統所需低功耗與高解析度需求，此研究採用連續時間OTA-C架構來實現類比濾波器，透過將運算轉導放大器操作於弱反轉區，以達到低功率消耗的目的，此外，為了簡化近身端系統架構及提高電路之線性度，此低功率濾波器提出一多差動輸出差動輸入電路，將過去文獻之OTA架構中使用電流分流技術之電流設計為另一差動輸出對，並保有原先降低轉導值之特性，而將整體電流重新分配後，可設計出二組輸出轉導值相同之輸出差動對。將此多差動輸出差動輸入運算轉導放大器配合系統簡化技巧，可將原本五階轉導電容式低通濾波器所需之運算轉導放大器個數由11個降至6個，直接減少了硬體成本與功率消耗，並提高整個濾波器的線性度(此架構在2015/2016年分別取得美國與中華民國發明專利、架構與電路實現測試在今年四月被IEEE TCAS II接受)，量測結果且考量功率消耗與動態範圍已證明具有全世界較佳的技術指標(Figure of Merit, FOM)。不過經由電路雜訊分析，此種多差動輸出差動輸入運算轉導放大器所產生之雜訊較傳統運算轉導放大器架構大，並限制整個類比前端電路之訊號雜訊比(Signal-to-Noise Ratio, SNR)，為了在不使用大電容減少濾波器雜訊考量下，我們引用了阻抗縮放電路(Impedance Scaler Circuit)技術，進一步提升類比濾波器的性能(已完成量測與論文撰寫，並投稿IEEE TBioCAS期刊)，相較於前一版本(2017/4 accepted by IEEE TCAS II)，技術指標可再進一步提升一個階數(order)。此晶片已由TSMC 0.18μm製程製作並量測，其核心面積為0.135 mm2。由量測結果顯示，在供應電壓1 V下，其功率消耗為390 nW，動態範圍為58.44 dB；當差動輸入訊號振幅為100 mV時，其總諧波失真低於-59 dB，而頻寬量測結果為250 Hz可以濾除心電訊號以外的雜訊干擾。

This study proposes a fifth-order Butterworth operational transconductance amplifier-C (OTA-C) low-pass filter (LPF) with multiple-output differential-input (MODI) OTA structure and metal–insulator–metal capacitors for electrocardiography applications. The current division technology is used as an alternative output pair to provide multiple outputs and achieve high linearity. This technique reduces the number of OTAs of the fifth-order LPF from 11 to 6 as compared with the conventional structure. The design issue of linearity and noise are also considered in the implementation of LPF. In order to achieve a filter with large-time constant and low noise, linearized MODI OTA structures with reduced transconductance and impedance scaler circuits for capacitors are used. OTA-based circuits is operated in the subthreshold region and supply voltage of 1V to conserve power consumption due to the battery life of the portable device and the critical area of the digital processor required in the circuit. The proposed filter is fabricated in a 0.18 µm complementary metal–oxide–semiconductor technology with a core area of 0.135 mm2. The experimental results show that the dynamic range (DR) is 58.44 dB, achieved a total harmonic distortion (THD) of -59 dB under a bandwidth of 250 Hz and input voltage of 100 mV at a 1 V supply voltage. The total power dissipation is 390 nW.

[1] F. Top ten causes of death by broad income group(2015). World health organization. Retrieved Jan. 18. http://www.who.int/mediacentre/factsheets/fs310/en/index.html.
[2] 工業技術研究院, http://www.bmes.org.tw/FCKupload/File/IEK_08.pdf
[3] 國科會計畫：【互動式智慧型健康照護與晶片系統-子計畫六：應用於多重標準/寬頻生醫通訊之低功率低雜訊射頻/混和訊號電路】；編號：NSC99-2220-E-194-006。
[4] S. Y. Lee and C. J. Cheng, “Systematic Design and Modeling of an OTA-C Filter for Portable ECG Detection,” IEEE Trans. Biomed. Circuits Syst., vol. 3, no. 1, pp. 53-64, Feb. 2009.
[5] J. Silva-Martínez and A. Vázquez-González, “Impedance scalers for IC active filters,” in IEEE Proc. ISCAS’98, vol. 1, Monterey, CA, pp. 151–153.
[6] C. Ølgaard and I. R. Nielsen, “Noise improvement beyond the ‘kT/C’ limit in low frequency C-T filters,” IEEE Trans. Circuits Syst.—II, vol. 43, pp. 560–569, Aug. 1996.
[7] J. G. Webster, Medical Instrumentation Application and Design, New York: Wiley, 1998.
[8] R. Castello and P. R. Gray, “Performance limitations in switched capacitor filters,” IEEE Trans. Circuits Syst. II, vol. CAS-32, pp. 865–876, Sept. 1985.
[9] R. Schaumann and M. E. V. Valkenburg, “Design of Analog Filters,” New York: Oxford, 2001.
[10] S. Winder, “Analog and Digital Filter Design, 2nd ed,” Newnes, 2002.
[11] S. Sinencio and J.S. Martinez, “CMOS transconductance amplifiers, architecture and active filters: a tutorial,” IEEE Proc. Circuits Devices Systems, Vol.147, p.p.3-12,, Feb. 2000.
[12] J. Silva-Martinez, M. S. J. Steyaert, and W. M. C. Sansen, “A large-signal very low-distortion transconductor for high-frequencycontinuous-time filters,” IEEE J. Solid-State Circuits, vol. 26, no. 7, pp. 946–955, Jul. 1991.
[13] S. Koziel and S. Szczepanski, “Design of highly linear tunable CMOS OTA for continuous-time filters,” IEEE Trans. Circuits Syst. II, Analog Digit. Signal Process., vol. 49, no. 2, pp. 110–122, Feb. 2002.
[14] E. A. Vittoz and J. Fellrath, “CMOS analog integrated circuits based on weak inversion operation,” IEEE J. Solid-State Circuits, vol. 12, no. 6, pp. 224–231, Jun. 1977.
[15] Y. Tsividis, Operation and Modeling of the MOS Transistor, 2nd ed. New York: McGraw-Hill, 1998.
[16] C.M. Kuo, “A Low Power Gm-C Filter for EEG Conditioning,” Master thesis, 2009.
[17] P. E. Allen and D. R. Holberg, “CMOS Analog Circuits Design,” New York: Oxford, 2002.
[18] B. Razavi, “Design of Analog CMOS Integrated Circuits,” McGraw-Hill, 2003.
[19] E. Rodriguez-Villegas, A. Yufera, and A. Rueda,“A 1.25-V micropower Gm-C filter based on FGMOS transistors operating in weak inversion,”IEEE J. Solid-State Circuits, vol. 39, no. 1, pp. 100-111, 2004.
[20] A. Veeravalli, E. Sanchez-Sinencio, and J. Silva-Martinez,“Transconductance amplifier structures with very small transconductances: a comparative design approach,”IEEE J. Solid-State Circuits, vol. 37, no. 1, pp. 770-775, 2002.
[21] J. Silva-Martinez and S. Solis-Bustos,“Design considerations for high performance very low frequency filters,”in Proc. IEEE Int. Symp. Circuits and Systems (ISCAS), vol. 2, pp. 648-651, 1999.
[22] P. Garde,“Transconductance cancellation for operational amplifiers,”IEEE J. Solid-State Circuits, vol. 12, no. 3, pp. 310-311, 1977.
[23] S. Solis-Bustos, J. Silva-Martinez, F. Maloberti, and E. Sanchez-Sinencio,“A 60-dB dynamic-range CMOS sixth-order 2.4-Hz low-pass filter for medical applications,”IEEE Trans. on Circuits and Systems II: Analog and Digital Signal Processing, vol. 47, no. 12, pp. 1391-1398, 2000.
[24] S. H. Yang, K. H. Kim, Y. H. Kim, Y. You, and K. R. Cho,“A novel CMOS operational transconductance amplifier based on a mobility compensation technique,”IEEE Trans. on Circuits and Systems II: Express Briefs, vol. 52, no. 1, pp. 37-42, 2005.
[25] K. C. Kuo and A. Leuciuc,“A linear MOS transconductor using source degeneration and adaptive biasing,”IEEE Trans. on Circuits and Systems II: Analog and Digital Signal Processing, vol. 48, no. 10, pp. 937-943, 2001.
[26] J.F. Tsai, “1-V Low-Power OTA-C Filter for ECG,” Master thesis, 2012.
[27] K. R. Laker and W. M. C. Sansen, Design of Analog Integrated Circuits and Systems. New York: McGraw-Hill, 1994.
[28] L. Luh, Jr. John-Choma, and J. Draper, “A Continuous-Time Common-Mode Feedback Circuit(CMFB) for High-Impedance Current Mode Application,” IEEE international conference on Electronics, Circuits and Systems, vol. 3, pp. 347-350, 1998.
[29] Z. Zhu and W. Bai, “A 0.5-V 1.3-μW analog front-end CMOS circuit,” IEEE Trans. Circuits Syst. II: Briefs, vol. 63, no. 6, pp. 523-527, June 2016.
[30] B. Bosselin, M. Sawan, and E. Kerherve, “Linear-phase delay filters for ultra-low-power signal processing in neural recording implants,” IEEE Trans. Biomed. Circuits Syst., vol. 4, no. 3, pp. 171-180, June 2010.
[31] X. Qian, Y. P. Xu, and X. Li, “A CMOS continuous-time lowpass notch filter for EEG systems,” Analog Integr. Circuits Signal Process., vol. 44, pp. 231–238, Jul. 2005.
[32] G. Domenech-Asensi, et. al., “Low-frequency CMOS bandpass filter for PIR sensor in wireless sensor nodes,” IEEE Sensors Journal, vol. 14, no. 11, pp. 4085-4094, Nov. 2014.
[33] Chuan-Yu Sun and Shuenn-Yuh Lee, “A fifth-order Butterworth OTA-C LPF with multiple-output differential-input OTA for ECG applications,” accepted by IEEE Trans. on Circuits and Systems-II: Express Briefs.
[34] Chuan-Yu Sun and Shuenn-Yuh Lee, “A low-power fifth-order Butterworth OTA-C lowpass filter with impedance scaler for portable ECG application,” submitted to IEEE Trans. on Biomedical Circuits and Systems
[35] C. Qian, J. Parramon, and E. Sanche-Sinencio, “A micropower low-noise neural recording front-end circuit for epileptic seizure detection,” IEEE J. Solid-State Circuits, vol. 46, no. 6, pp. 1392–1405, Jun. 2011.
[36] T.-Y. Wang et al., “A fully reconfigurable low-noise biopotential sensing amplifier with 1.96 noise efficiency factor,” IEEE Trans. Biomed. Circuits Syst., vol. 8, no. 3, pp. 411–422, Jun. 2014.