近幾年來不同生醫應用層面的植入式生理訊號量測系統發展趨向於微小化並搭配無線方式傳輸訊號。以整體系統來看，從電極端接收的生理訊號極為微弱，為了完整地記錄生理訊號，其電路設計上朝向低雜訊、高解析度、低功率消耗等特點邁進。
本篇主旨為提出一應用於生醫訊號量測系統之全差動對稱式類比前端電路，可針對極微弱的神經電圖(Electromyography, ENG)訊號作一記錄。為了將其中低頻的非理想成份諸如閃爍雜訊、直流偏移電壓等消除，提高其訊號雜訊比，以增加記錄的神經訊號的可辨度，本電路中放大級採用截波穩定型的技術。再者，為了降低整體電路的功率消耗，將輸入級的場效電晶體操作於弱反轉區。而截波穩定型放大器當中的帶通濾波器使用不同於一般濾波器的實現方式完成。本文提出架構由差動差分放大器與米勒積分器所構成，此架構可將從電極與電解溶液介面而產生的直流偏移電壓消除。
本文所提整體類比前端電路包含偏壓電路、時脈產生器、截波穩定型放大器、後置放大器、和二階連續時間低通濾波器。在電路實現上，在有效頻寬約9.3 KHz下，其直流電壓增益達到62.9 dB、總等效輸入相關雜訊電壓約為7.05 μVrms、其有效位元數達到10位元的解析度。使用台積電0.18 μm 標準CMOS 1P6M製程完成，其晶片面積為0.88 x 0.43 mm2。在1.8 V電源供應下，總功率消耗約為230 μW。

In recent years, the implanted bio-signal measurement devices for various bio-medical applications tend to be minimized and with wireless transmission capabilities. Since physiological signals from electrodes are very tiny and are difficult to be recorded, design of the bio-signal analog-front-end circuits are always with the features of low-noise, high resolution, and low power consumption.
This work presents a fully differential and analog-front-end circuit for bio-signal measurement system that can be used to record the very tiny electroneurography (ENG) signals. Chopper stabilization technique (CHS) is employed in the amplification stage to eliminate the non-ideal low-frequency effects, such as the flicker noise and the DC-offset voltage. It improves the signal-to-noise ratio (SNR) and offers a higher resolution for the recorded neuron signals. In order to decrease the power dissipation of the system, input stages of field-effect transistors are designed to be operating at the weak-inversion region. In addition, the band-pass filter of the chopper-stabilized amplifier consists of a differential difference amplifier and a Miller integrator, which are different to the traditional design with passive resistors and capacitors. The purpose of this BPF is aimed to cancel out the DC-offset voltage from the electrode-electrolyte interface.
The whole AFE circuit includes a bias circuit, a clock generator, a chopper stabilization amplifier, a post-amplifier, and a second-order continues-time low-pass filter. Such AFE circuit is implemented in the TSMC 0.18-μm one-poly six-metals CMOS process and provides a mid-band gain of 62.9 dB, a signal bandwidth approximates up to 9.3 KHz, a total equivalent input-referred noise of about 7.05 μVrms, and a 10-bit resolution. Supplied at 1.8 V, the proposed AFE circuit consumes around 230 μW. The chip area is 0.88 × 0.43 mm2.

[1] J. G. Webster, “Medical instrumentation application and design,” Canada: John Wiley & Sons, Inc., 1998.
[2] M. F. Bear, B. W. Connors, and M. A. Paradiso, “Neuroscience: exploring the brain,” Baltimore: Lippincott Williams & Williams Inc., 1996.
[3] K.D. Wise, “A multi-channel microprobe for biopotential recording,” Ph.D. dissertation, Stanford, CA, 1969.
[4] C. T. Charles, “Electrical components for a fully implantable neural recording system,” The University of Utah, Aug. 2003.
[5] M. Dagtekin, “A chopper modulated amplifier system design for in vitro neural recording,” North Carolina State University, 2006.
[6] J. W. Lu, “Analysis and design of electrical stimulator and impedance measurement circuitry for visual prostheses,” Nation Central University, Jul. 2008.
[7] A. B. Schwartz, X. T. Cui, D. J. Weber, and D. W. Moran, “Brain controlled interfaces: movement restoration with neural prosthetics,” Neuron, vol. 52, pp. 205–220, 2006.
[8] S. C. Lee, “Design of implantable wireless bidirectional SOC for biomedical applications,” National Chung Cheng University, Oct. 2006.
[9] J. J. Sit and R. Sarpeshkar, “A low-power blocking-capacitor-free charge-balanced electrode-stimulator chip with less than 6 nA DC error for 1-mA full-scale stimulation,” IEEE Trans. Biomed. Circ. Syst., vol. 1, no. 3 , pp. 184-192, Sep. 2007.
[10] B. Razavi, “Design of analog CMOS integrated circuits,” New York: McGraw-Hill, 2001.
[11] C.C. ENZ and G.C. Temes, “Circuit techniques for reducing the effects of op-amp imperfections： autozeroing, correlated double sampling, and chopper stabilization,” Proc. IEEE, vol. 84, no. 11, pp. 1584-1614, Nov. 1996.
[12] J. H. Tun, “The design and implementation of fully-differential chopper-stabilized operational amplifier,” National Chi Nan University, Jul. 2004.
[13] D. A. Johns and K. Martin, “Analog integrated circuit design,” New York: John Wiley and Sons Inc., 1997.
[14] P. R. Gray, P. J. Hurst, S. H. Lewis, and R. G. Meyer, “Analysis and design of analog integrated circuits,” New York: John Wiley & Sons, Inc., 2001.
[15] T. M. Hollis, D. J. Comer, and D. T. Comer, “Optimization of MOS amplifier performance through channel length and inversion level selection,” IEEE Trans. Circ. Syst.-II: Express Briefs, vol. 52, no. 9, Sep. 2005.
[16] D. M. BINKLEY, B. J. BLALOCK, and J. M. ROCHELLE, “Optimizing drain current, inversion level, and channel length in analog CMOS design,” Proc. Analog Integrated Circuits and Signal, vol. 47, no. 2, pp. 137-163, May 2006.
[17] T. Denison, K. Consoer, W. Santa, A.-T. Avestruz, J. Cooley, and A. Kelly , “A 2 μW 100 nV/rtHz chopper-stabilized instrumentation amplifier for chronic measurement of neural field potentials,” IEEE J. Solid-State Circ., vol. 42, no. 12, pp. 2934-2945, Dec. 2007.
[18] C. C. Enz, E. A. Vittoz, and F. Krummenacher, “A CMOS chopper amplifier,” IEEE J. Solid-State Circ., vol. 22, no. 3, pp. 335-342, Jun. 1987.
[19] A. Bakker and J. Huijsing, “High-accuracy CMOS smart temperature sensors,” Boston: Kluwer Academic Publisher, 2000.
[20] C. Menolfi and Q. Huang, “A low-noise CMOS instrumentation amplifier for thermoelectric infrared detectors, ” IEEE J. Solid-State Circ., vol. 32, no. 7, pp. 968-976, Jul. 1997.
[21] C. Menolfi and Q. Huang, “A fully integrated CMOS instrumentation amplifier with submicrovolt offset,” IEEE J. Solid-State Circ., vol. 34, no. 3, pp. 415-420, Mar. 1999.
[22] C. Menolfi and Q. Huang, “A chopper modulated instrumentation amplifier with first order low-pass filter and delayed modulation scheme,” Proc. ESSCIRC ''99., pp. 54-57, Sep. 1999.
[23] B. Gosselin, A. E. Ayoub, and M. Sawan, “A low-power bioamplifier with a new active DC rejection scheme,” IEEE Intl. Symp. Circ. Syst., pp. 21-24, May 2006.
[24] B. Gosselin, M. Sawan, and C. Andrew Chapman, “A low-power integrated bioamplifier with active low-frequency suppression,” IEEE Trans. Biomed. Circ. Syst., vol. 1, no. 3 , pp. 184-192, Sep. 2007.
[25] H. Alzaher and M. Ismail, “A CMOS fully balanced differential difference amplifier and its applications,” IEEE Trans. Circ. Syst.-II: Analog and Digital Signal Processing, vol. 48, no. 6, Jun. 2001.
[26] P. E. Allen and D. R. Holberg, “CMOS analog circuit design,” New York: Oxford University Press, 2002.
[27] M. M. Zhang and P. J. Hurst, “Effect of nonlinearity in the CMFB circuit that uses the differential-difference amplifier,” IEEE Intl. Symp. Circ. Syst., pp. 1390-1393, May 2006.
[28] R. Schaumann and M. E. Van Valkenburg, “Design of analog filters,” Oxford University Press, 2001.
[29] S. Y. Ho, “A continuous-time receive filter design with automatic gain control for DVB-T/H receiver,” Nation Central University, Oct. 2007.
[30] R. H. Olsson III, M. N. Gulari, and K. D. Wise, “A fully-integrated bandpass amplifier for extracellular neural recording,” IEEE EMBS, pp. 165-168, Mar. 2003.
[31] R. R. Harrison and C. Charles, “A low-power low-noise CMOS amplifier for neural recording applications,” IEEE J. Solid-State Circ., vol. 38, no. 6, pp. 958-965, Jun. 2003.
[32] R. J. Baker, “CMOS circuit design, layout, and simulation,” NJ: Wiley IEEE Press, 2005.
[33] A. Tajalli, Y. Leblebici , and E. J. Brauer, “Implementing ultra-high-value floating tunable CMOS resistors,” Electronics Letters, vol. 44 no. 5, Feb. 2008.
[34] M. S. J. Steyaert, W. M. C. Sansen, and C. Zhongyuan, “A micropower low-noise monolithic instrumentation amplifier for medical purposes,” IEEE J. Solid-State Circ., vol. sc-22, no. 6, pp. 1163-1168, Dec. 1987.
[35] http://www.physionet.org/physiobank/database/tremordb/.
[36] Y. Hu and M. Sawan, “CMOS front-end amplifier dedicated to monitor very low amplitudesignal from implantable sensors,” Proc. Analog Integrated Circuits and Signal Processing, vol. 33, no. 1, pp. 29-41,Oct. 2002.
[37] T. Lim and Y. P. Xu, “A low-power and low-offset CMOS front-end amplifier for portable EEG acquisition system,” IEEE Inte. Work. Biom. Circ. Syst., pp. 17-20, Dec. 2004.
[38] A. Uranga, X. Navarro, and N. Barniol, “Integrated CMOS amplifier for ENG signal recording,” IEEE Trans. Biomed. Eng., vol. 51, no. 12, pp. 2188-2194, Dec. 2004.
[39] K. A. Ng and P. K. Chan, “A CMOS analog front-end IC for portable EEG/ECG monitoring applications,” IEEE Trans. Circ. Syst.-I: vol. 52, no. 11, Nov. 2005.
[40] P. K. Chan, G. A. Hanasusanto, H. B. Tan, and V. K. S. Ong, “A micropower CMOS amplifier for portable surface EMG recording, ” IEEE Asia Pacific Conf. Cir. Syst., pp. 490-493, Dec. 2006.
[41] T. Denison, K. Consoer, W. Santa, A.-T. Avestruz, J. Cooley, and A. Kelly, “A 2uW 100nv/rtHz chopper-stabilized instrumentation amplifier for chronic measurement of neural field potentials,” IEEE J. Solid-State Circ., vol. 42, no. 12, pp. 2934-2945, Dec. 2007.