Ultra-Low-Power Sensor Signal Monitoring and Impulse Radio Architecture for Biomedical Applications M. R. Haider † † Department of Engineering Science Sonoma State University Rohnert Park, CA 94928 mhaider407@gmail.com A. B. Islam ‡ , S. K. Islam ‡ ‡ Department of Electrical Engineering and Computer Science The University of Tennessee Knoxville, TN 37996-2100 sislam@utk.edu Abstract— Remote diagnostics of patient’s vital information and initiation of necessary actions have resulted in the development of wireless body area network (WBAN). For almost zero maintenance of each sensor node within a WBAN, each node must work with a power consumption less than 100μW which can be achieved employing impulse radio architecture. In this work a low-power transmitter has been presented. The unit manifests a Data Generator Block, an Impulse Generator Block and a Buffer. The Data Generator Block converts any electrochemical sensor current in the range of 0.2μA to 2μA to digital data. The circuit can operate with a supply voltage of 1V and consume a power in the range of 0.427µW to 3.5µW. The Impulse Generator Block utilizes a RC network to generate impulses of approximately 110ns duration. Finally a Buffer circuit is used to drive a standard 50Ω load which could be an external antenna. The peak current consumption of the impulses is 2.81mA with peak output voltage of 140.2mV that makes it extremely suitable for short range wireless communication. The entire system has been designed and simulated using 0.35-μm standard CMOS process. The average power consumption of the system is only 68.30μW. Keywords-sensors;impulse radio;ultra-low-power;biomedical; I. INTRODUCTION Metabolic monitoring of various human physiological parameters has been an intensive research area since the past decade. Continuous in vivo monitoring and long term reliable operation of the system is the key feature of any implantable sensor system. Recent technological breakthrough of micro- and nano-fabrication processes have led to the development of various miniature, light weight, cost effective and energy efficient sensors for biomedical applications such as monitoring of glucose, lactate, pH, CO 2 , O 2 , etc. Fig. 1 shows the block diagram of an implantable sensor system. Variation of sensor signal requires an electronic circuit to convert the changes into a digital data and transmit the data outside of the biological environment for further diagnostics and processing. Powering the sensor and the data generator unit is a crucial issue. Power transfer using tethered cables can create skin infections and irritation [1]. Use of battery can cause biohazard due to the potential leakage of hazardous battery fluid. Power transfer to the implanted unit using inductive power link shows greater promises and does not show any of the above mentioned problems [2]. However the inductive power link is suitable only for low-voltage and low-power operation. Therefore for long term reliable operation of inductively powered implant unit, the unit must work with low-voltage low-power operation. In the recent years the need to develop efficient implantable medical devices has pushed the industry to design circuits with low supply voltage and low power consumption. The use of cascode structure yields high output impedance and therefore it is an attractive design choice. However, for supply voltage of less than 2V, the cascode circuits are often not feasible due to the reduced voltage headroom. In this sub- micron CMOS era, supply voltage is decreasing with each technological leap but the threshold voltage and drain-source saturation voltage are not scaling down at the same rate due to the sub-threshold current considerations for digital circuit in the mixed-signal environment [3] thereby limiting the supply voltage headroom and causing many difficulties and challenges for analog and RF circuit designers. To overcome these problems several techniques have been reported [4] such as the use of (a) bulk driven MOSFET (b) floating gate MOSFET, and (c) self-cascode structure. Another excellent choice for the design of low-power circuit is the use of subthreshold MOSFET [5]. MOSFET operating in subthreshold region offers extremely low-power operation. In subthreshold region, MOSFET shows exponential behavior of drain current variation with gate bias voltage and offers higher transconductance efficiency (g m /I d ). A higher g m /I d allows the circuit to achieve desired performance at low power. 2010 IEEE Annual Symposium on VLSI 978-0-7695-4076-4/10 $26.00 © 2010 IEEE DOI 10.1109/ISVLSI.2010.81 222