A Generic Multielement Microsystem for Portable Wireless Applications ANDREW MASON, NAVID YAZDI, ABHIJEET V. CHAVAN, KHALIL NAJAFI, SENIOR MEMBER, IEEE, AND KENSALL D. WISE, FELLOW, IEEE Invited Paper An open-architecture microsystem that can be populated with a variety of sensors and actuators is described. The microsys- tem is designed for low-power wireless applications where small size and high sensor accuracy are important. It consists of an in-module microcontroller connected to multiple front-end trans- ducers through an intramodule sensor bus. An external interface allows internally processed data to be output through either a hard-wired input/output port or a radio-frequency transmitter. The present microsystem is configured for environmental monitoring and measures temperature, barometric pressure, relative humidity, and acceleration/vibration. It occupies less than 10 cc, consumes an average of 530 W from 6 V, and transmits data up to 50 m. System features such as active power management, the intramodule sensor bus, generic bus interface circuitry, and in-module sensor compensation based on bivariate polynomials are discussed. Keywords— Compensation, measurement system, microelectro- mechanical devices, microelectromechanical system, microsensor, microsystem, power management, transducer. I. INTRODUCTION Driven by rapid advances in microcomputers and global connectivity, many of the most important emerging markets for microelectronics require the ability to gather information from the nonelectronic world [1], [2]. Examples include health care (diagnostic and therapeutic devices, prosthetics), automotive systems (smart vehicles and smart highways), automated manufacturing [including smart very-large-scale- integration (VLSI) process tools], environmental moni- toring and control devices, defense systems, and many consumer products. Using integrated circuit technology and extensions of it, integrated sensors and microactuators are being developed to provide the necessary input/output (I/O) devices. These are increasingly being realized combined with hybrid or monolithic circuitry on a common substrate Manuscript received November 24, 1997; revised January 14, 1998. This work was supported by the Defense Advanced Research Project Agency under Contract J-FBI-92-149. The authors are with the Center for Integrated Sensors and Circuits, De- partment of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, MI 48109-2122 USA. Publisher Item Identifier S 0018-9219(98)05096-8. [3]–[6] and have come to be known as microelectrome- chanical systems (MEMS). Merging these devices with increasingly powerful digital signal-processing electronics now makes it possible to go beyond simple analog readout circuitry and form complete closed-loop microsystems in very small, highly integrated modules. These autonomous microsystems are capable of gathering data from the phys- ical world, converting them to electronic form, compen- sating them for interfering variables and nonlinearities, and either acting on the information directly or transferring it to other systems [7]–[9]. Such microsystems can be expected to have a significant and pervasive impact on a large number of applications during the coming decade. As used in this paper, a “microsystem” is defined as a collection of highly integrated devices that con- tains transducers along with appropriate interface circuitry and is capable of performing multiple tasks autonomously as well as responding intelligently to various commands from a host system. This definition helps to identify the class of devices being considered and illustrates the differences between a mi- crosystem and a less complex “smart” sensor. Reflecting general trends in microelectronics, many of the emerging applications for microsystems demand small portable wire- less devices [10]–[12] having high accuracy and the ability to perform in distributed instrumentation systems collecting data over a broad physical area [13]. It is significant that in applications as diverse as personal health monitors, implantable neural prostheses, sensors for VLSI process control, sentries for battlefield awareness, and sensors for unmanned air reconnaissance, a single generic open system architecture applies. Such systems are customized by the sensors and actuators populating them and by the software used in their resident microcontrollers. While not every application shares the same power or telemetry range requirements, a common system framework can be shared and provides a basis for defining the standards that will be 0018–9219/98$10.00  1998 IEEE PROCEEDINGS OF THE IEEE, VOL. 86, NO. 8, AUGUST 1998 1733