近幾年，隨著CMOS-MEMS製程的進步，微機電麥克風取代了傳統的架構成為主流，應用於不同的消費性電子產品上，如行動裝置、助聽器等。當感測器與讀出電路整合在單一晶片上時，由於微機電麥克風的電容變化量範圍約femto-Farad，所以一低雜訊的信號轉移方式於讀出電路來說顯得非常重要。

為符合低頻時低雜訊低成本的應用，本論文選擇於0.35um CMOS標準製程下設計一接面電晶體(JFET)元件當作讀出電路的輸入緩衝器使用，藉JFET特性來排除掉輸入相關雜訊的影響。為驗證JFET之可行性，多設計一MOSFET的對照組來比較。接著利用一低雜訊放大器來放大微小感測訊號，並利用高動態範圍的積分三角調變器做信號處理。模擬結果SDM部分訊號對雜訊與失真比可達70.4dB，動態範圍達102.9dB，整體讀出電路部分訊號對雜訊與失真比69.8dB，單一核心的面積為556umx381um。

In recent years, with the progress of CMOS-MEMS tech-nology, MEMS microphone gradually replaced the traditional Electret Condenser Microphone(ECM)and became the mainstream in consumer electronic products such as various mobile devices and hearing aids. When the sensor and the readout circuit are integrated together as a system-on-a-chip (SoC), because the capacitive variation of MEMS microphone is in the range of femto-Farad, a low-noise signal-translation in the readout circuit is very important.

In order to meet the requirements for low-noise, low-cost applications in the sound frequency (low frequency) range, this work uses a junction field effect transistor (JFET), which is integrated in the 0.35um CMOS standard process, as the input device for the readout circuit so as to reduce the input referred low-frequency noise. In addition, a MOSFET is in comparison with the JFET to verify the feasibility. The readout circuit includes a low-noise amplifier and a high dynamic range sigma-delta modulator (SDM) to process the signal. The simulated results of the SDM show that the peak SNDR and the dynamic range are 70.4dB and 102.9dB, respectively. The peak SNDR of the readout circuit is 69.8dB. The chip size is 556um x 381um.

[1]Knowles Electronic website, http://www.knowles.com
[2]Yole Développement website, http://www.yole.fr
[3]SC. Ko, CH. Jun, WI. Jang, CA. Choi, “Micromachined air-gap structure MEMS acoustic sensor using reproducible high-speed lateral etching and CMP process,” J. Micromech. Microeng. vol. 16, pp.2071-2076, 2006.
[4]N. Yazdi, H. Kulah, K. Najafi, ”Precision readout circuits for capacitive micro- accelerometers,” IEEE Sensors, pp. 24–27, 2004.
[5]A. Dec, H. Akima, R. Mohn, K. Suyama, “Audio Pre-Amplifiers for Digital Electret Microphones in 0.18um CMOS Process,” IEEE International Symposium on Circuits and Systems, pp. 2489-2492, May 2009.
[6]M. W. Baker, R. Sarpeshkar, “A Low-Power High-PSRR Current-Mode Microphone Preamplifier”, IEEE J. Solid-state Circuits, vol. 38, no. 10, pp. 1671-1678, Oct. 2003.
[7]B. Razavi, Design of Analog CMOS Integrated Circuits, McGraw-Hill International Edition, 2001.
[8]F. A. Levinzon, “Noise of the JFET Amplifier,” IEEE Trans. Circuits Syst. I, Fundam. Theory Appl., vol. 47, pp. 981-985, July 2000.
[9]H. Takao, R. Asaoka, K. Sawada, S. Kawahito, M. Ishida, “A JFET-CMOS technology for low-noise sensor interface circuits,” IEEJ Trans. Sensors and Micromachines, vol. 123, no. 10, pp. 422-428, 2003
[10]B. George, S. Agrawal and V. J. Kumar, “Switched-Capacitor Sigma-Delta Capacitance to Digital Converter Suitable for Differential Capacitive Sensors,” IEEE Instrumentation and Measurement Technology Conference Proceedings, IMTC 2007, pp. 1-5, May 2007.
[11]J. O’Dowd, A. Callanan, G. Banarie, “Capacitive sensor interfacing using sigma- delta techniques,” IEEE Sensors, pp.951–954, Nov. 2005.
[12]Y. Fu, H. Wong b, J.J. Liou, “Characterization and modeling of flicker noise in junction field-effect transistor with source and drain trench isolation,” Microelectronics Reliability, vol. 47, pp. 46–50, Jan. 2007.
[13]Adel S. Sedra, Kenneth C. Smith, “Microelectronic Circuits,” Oxford, New York, 1998.
[14]W. Buttler, B. J. Hosticka, “All-JFET Amplifiers For Low Noise Applications,” Solid-State Circuits Conference, ESSCIRC '89. pp. 133-136, Sept. 1989.
[15]Jhih-Yuan Sie, “A High-speed and Low-power Continuous-time Sigma-Delta Modulator in 0.35-um CMOS Technology,” Institute of Electronic Engineering, National Tsing Hua University, June 2010.
[16]R. Schreier and Gabor C. Temes, “Understanding Delta-Sigma Data Converters,” Wiley, 2005, ISBN:0-471-46585-2.
[17]Bernhard E. Boser, Bruce A. Wooley, “The Design of Sigma-Delta Modulation Analog-to-Digital Converters,” IEEE J. Solid-State Circuits, vol. 23, pp. 1298-1308, Dec. 1988.
[18]Professor Jieh-Tsorng Wu, Class Note from Data-Conversion Integrated Circuits , Electronic Engineering, National Chiao Tung University, Taiwan.
[19]S. Brigati, F. Francesconi, P. Malcovati, D. Tonietto, A. Baschirotto and F. Maloberti, “Modeling Sigma-Delta Modulator Nonidealities in Simulink,” Proceedings of IEEE International Symposium on Circuits and Systems (ISCAS ‘99), pp.384-387, 1999.
[20]P. Malcovati, S. Brigati, F. Francesconi,F. Maloberti, P. Cusinato, and A. Baschirotto, “Behavioral modeling of switched-capacitor sigma-delta modulators,” IEEE Trans. Circuits Syst. I, Fundam. Theory Appl., vol. 50, no. 3, March 2003.
[21]Fu-Chuang Chen and Chun-Chieh Huang, “Analytical Settling Noise Models of Single-Loop Sigma–Delta ADCs,” IEEE Transactions on Circuits and Systems II: Express Briefs, vol.56, pp. 753-757, Oct. 2009.
[22]Professor Fu-Chuang Chen, Class Note from Sigma-Delta-Modulator Data Converters, Dep. Of Electrical and Computer Engineering, National Chiao Tung University, Taiwan.
[23]Jawed, S.A.; Cattin, D.; Gottardi, M.; Massari, N.; Baschirotto, A.; Simoni, A. “A 828μW 1.8V 80dB dynamic-range readout interface for a MEMS capacitive microphone,” Solid-State Circuits Conference, 2008. ESSCIRC 2008. 34th European, pp.442-445, 2008.
[24]Jawed, S.A.; Cattin, D.; Massari, N.; Gottardi, M.; Baschirotto, A., “A MEMS Microphone with Force-Balancing and Charge-Control,” Research in Microelectronics and Electronics, PRIME 2008, pp. 97-100, 2008.
[25]L. Yao, M. Steyaert, W. Sansen, “A 0.8-V, 8-µW, CMOS OTA with 50-dB Gain and 1.2-MHz GBW in 18-pF Load,” Proc. European Solid-State Circuit Conf, pp.297-300, Sept. 2003.
[26]National Semiconductor, LM117/LM317A/LM317 3-Terminal Adjustable Regulator Data Sheet, National Semiconductor, 1997.
[27]L. Picolli, M. Grassi, L. Rosson, A. Fornasari, and P. Malcovati, “A Fourth-Order, Audio-Bandwidth, 87.5-dB SNDR Σ∆ Modulator for MEMS Microphones,” IEEE International Symposium on Circuits and Systems, pp. 1325-1328, May 2009.
[28]H. B. Le, J. W. Nam, S. T. Ryu, S. G. Lee, “Single-chip A/D converter for digital microphones with on-chip preamplifier and time domain noise isolation,” Electronics Letters, Vol. 45, Issue:3, pp. 151-153, Jan. 2009.
[29]L. Picolli, M. Grassi, L. Rosson, P. Malcovati, A. Fornasari, “A 1.0mW, 71dB SNDR, -1.8dBFS Input Swing, Fourth-Order Σ∆ Interface Circuit for MEMS Microphones,” Proc. European solid-state circuits conference, pp.324-327, 2009.
[30]National Chip Implementation Center Web Site, http://www.cic.org.tw/cic_v13/
[31]M. Luo, C. Lin, “Behavioral modeling of discrete domain sigma-delta modulators,” Anti-counterfeiting, Security and Identification, 2008. pp. 387-390, Aug. 2008.
[32]H. Zare-Hoseini, I. Kale, O. Shoaei, “Modeling of switched-capacitor delta-sigma modulators in SIMULINK,” IEEE Trans. Instrumentation and Measurement, vol. 5, pp. 1646-1654, Aug. 2005.