A 1.8 V CMOS fourth-order Gm-C bandpass sigma-delta modulator dedicated to front-end ultrasonic receivers

A 4th order bandpass sigma-delta modulator for ultrasound applications is presented. By cascading two second-order identical Gm-C bandpass filters, a 4th-order modulator was designed with high power-efficiency, stability, tunability and programmability. The modulator is dedicated for application with intermediate frequency of 3 MHz and bandwidth of 200 kHz. Implemented in a standard 0.18 μm CMOS technology, the post-layout simulation of the modulator gives a dynamic range of 78 dB. Chip measurements are reported after successfully tuning the modulator to operate at four-time of its folded specifications. The final SNR achieves 58 dB at 0.75 MHz with 50 kHz bandwidth. The modulator consumes 2.5 mW from 1.8 V power supply. Moreover, a programming method is introduced and corresponding circuit is designed to change the central frequency of the modulator between 3 and 20 MHz for scanning different regions of the body. However the 200 kHz bandwidth limits the modulator only for Dobbler mode applications, the effective facilities of programmability are valuable property to expand this application to other wide band applications in future. Lisheng Qin received the B.Sc. degree in electrical engineering from Tianjin University, China in 1992. He was with Polystim Neurotechnologies Laboratory from 2001 to 2005 and received the M.Sc. degree in electronics engineering from Ecole Polytechnique de Montreal, Canada in 2005. He is now with Apexone Microelectronics Inc. as Analog/Mixed-Signal Design Engineer. Kamal El-Sankary received the B.Sc. degree in electrical engineering from the Lebanese University, Lebanon in 1997 and the M.Sc. degree in electronics engineering from University of Quebec in Trois Rivieres, Canada, in 2001. He is currently pursuing the Ph.D. degree in microelectronics at Ecole Polytechnique de Montreal, Canada. His research interests include analog/mixed-signal circuits design and signal processing. Mohamad Sawan received the B.Sc. degree in electrical engineering from Université Laval, Canada in 1984, the M.Sc. and Ph.D. degrees, both in electrical engineering, from Université de Sherbrooke, Canada, in 1986 and 1990 respectively, and postdoctorate training from McGill University, Canada in 1991. He joined Ecole Polytechnique de Montréal in 1991 where he is currently a Professor in Microelectronics. His scientific interests are the design and test of mixed-signal (analog, digital and RF) circuits and systems, the digital and analog signal processing, the modeling, design, integration, assembly and validation of advanced wirelessly powered and controlled monitoring and measurement techniques. These topics are oriented toward the biomedical implantable devices and telecommunications applications. Dr. Sawan is a holder of a Canadian Research Chair in Smart Medical Devices. He is leading the Microelectronics Strategic Alliance of Quebec (Regroupement stratégique en microélectronique du Québec - ReSMiQ). He is founder of the Eastern Canadian IEEE-Solid State Circuits Society Chapter, the International IEEE-NEWCAS conference, and Polystim neurotechnologies laboratory at the Ecole Polytechnique de Montreal. He is cofounder of the International Functional Electrical Stimulation Society (IFESS), and the IEEE International conference on Electronics, Circuits and Systems (ICECS). Dr. Sawan is involved in the committees of many national and international conferences and other scientific events. He published more than 300 papers in peer reviewed journals and conference proceedings and is awarded 6 patents. He is editor of the Springer Mixed-signal Letters, Distinguished Lecturer for the IEEE CAS Society, President of the biomedical circuits and systems (BioCAS) technical committee of the IEEE CAS Society, and he is representative of IEEE-CAS in the International Biotechnology council. He received the Barbara Turnbull 2003 award for spinal cord research, the Medal of Merit from Lebanon, and the Bombardier Medal from the French Association for the advancement of sciences. Dr. Sawan is Fellow of the Canadian Academy of Engineering, and Fellow of the IEEE.