An Abstract of Development of an Implantable Data Acquisition System Prachi Santosh Sonalkar Submitted in partial fulfillment of the requirements for The Master of Science in Bioengineering The University of Toledo August 2005 Implantable medical devices offer several fascinating possibilities for improving human health. Coupled with advancements in the miniaturization of electronic systems, the array of implantable medical devices will continue to expand. Furthermore, if instrumentation based implants are interfaced to a communication sub-system, the potential exists for wireless microcontroller software updates and real-time data acquisition from integrated sensors which could relay patient health information or implant mechanical conditions to an external system. This thesis focuses on development of such a platform. The current system incorporates a Radio Frequency (RF) telemetry system integrated to an embedded microcontroller with multi-channel data acquisition capabilities. This system employs a XE1201A (Xemics Inc, Switzerland) transceiver chipset providing a bi-directional 405 MHz RF communications link. This transceiver is integrated to an ultra-low power MSP430F149 (Texas Instruments, Dallas TX) i microcontroller with 12-bit analog to digital capabilities. In addition, a similar external system is interfaced to a PC for complete control and real-time data acquisition is developed, a custom developed script language is implemented to input required commands for collection of desired data from a particular sensor. The software code and protocol to establish bi-directional communication was developed in ANSI C which is implemented on the microcontroller and the PC interface was developed using LabVIEW (National Instruments, Austin TX). In addition, all ASICs are available in die form to allow for ultra-miniaturization. The system was evaluated in a spinal disc implant equipped with strain and temperature sensors. Future work will involve manufacturing the entire system in an ultra-compact package through the use of flip-chip technology. ii ACKNOWLEDGEMENTS I would like to acknowledge the partial support by the Ohio Department of Development and the AO Research Foundation for this project. I would like to especially thank my advisor Dr. Brent Cameron for his constant assistance, encouragement, and excellent guidance throughout my graduate education. Furthermore, I also wish to thank my thesis committee members, Dr. Fournier and Dr. Molitor for their valuable advice on this thesis. In addition, I would like to thank my colleagues Mr. Fadel Mahfouz, Mr. Kirankumar Samudrala, Mr. Mihir Tambe, Ms. Sunita Gopalakrishnan, Ms. Swetha Krishnan, Mr. William (Bill) Levicky, and Mrs. Yanfang Li for their great help in this study and research and suggestions on this thesis. I would like to thank my parents, my in-laws, my brother and all my friends who are always there for support and encouragement and last but definitely not the least I would like to thank my husband Santosh for always being there for me. iii TABLE OF CONTENTS 1 INTRODUCTION.............................................................................. 1 1.1 MOTIVATION ........................................................................................................2 1.2 OVERVIEW OF THE IMPLANTABLE DATA ACQUISITION SYSTEM...............................3 1.3 ROLE OF RF TELEMETRY .....................................................................................5 1.3.1 Radio Communication....................................................................................6 1.3.2 Demodulation and Detection..........................................................................7 1.3.3 Coding and Error Detection ...........................................................................8 1.3.3.1 Manchester Encoding............................................................................8 1.3.3.2 Parity Check...........................................................................................9 1.4 FCC STANDARDS FOR MEDICAL IMPLANTS.........................................................10 1.4.1 MICS Band...................................................................................................10 1.4.2 WMTS Band.................................................................................................12 2 THEORY....................................................................................... 13 2.1 DATA ACQUISITION SYSTEM...............................................................................13 2.2 MSP430 MICROCONTROLLER............................................................................15 2.2.1 Features.......................................................................................................15 2.2.2 Pin Designations..........................................................................................16 2.2.3 Functional Block Diagram............................................................................17 2.2.3.1 Oscillator/Clock Subsystem .................................................................18 2.2.3.2 Flash Memory (JTAG)..........................................................................19 2.2.3.3 ADC12 Module.....................................................................................19 2.2.4 Electrical Characteristics over Operating Temperature Range....................20 2.3 DIGITAL RF WIRELESS UHF TRANSCEIVER XE1201A ........................................21 2.3.1 Features.......................................................................................................22 2.3.2 Pin designations...........................................................................................23 2.3.3 Functional Block Diagram............................................................................24 2.3.4 External Components Design ......................................................................25 2.3.4.1 SAW Resonator Circuit ........................................................................25 2.3.4.2 LNA Tank Circuit..................................................................................26 2.3.4.3 Up Converter Tank Circuit....................................................................27 2.3.4.4 LO Tank Circuit ....................................................................................27 2.3.5 Electrical Characteristics..............................................................................28 2.4 MAXIM SILICON OSCILLATOR..............................................................................29 2.5 EXTERNAL BATTERY RECHARGING SYSTEM .......................................................31 2.6 INTEGRATION WITH BIOCHEMICAL AND PHYSIOLOGICAL SENSORS .......................31 2.6.1 Challenges for Real Time Monitoring...........................................................31 2.7 POWER REQUIREMENT CONSIDERATIONS ..........................................................32 2.7.1 Monitoring Implant Conditions .....................................................................33 2.8 SENSOR FABRICATION .......................................................................................34 2.9 USE OF INBUILT ADC12 AND MULTIPLEXER ........................................................35 2.10 INTEGRATED TEMPERATURE SENSOR.................................................................36 2.11 FLIP-CHIP TECHNOLOGY ....................................................................................37 iv 3 MATERIALS AND METHODS.......................................................... 39 3.1 MICROCONTROLLER AND TRANSCEIVER INTERFACE............................................41 3.2 EVALUATING TRANSCEIVER PERFORMANCE IN A BODY PHANTOM .......................42 3.3 DEVICE DRIVER DEVELOPMENT: PORTABILITY AND TOOLS..................................42 3.3.1 Tool for Driver Development........................................................................43 3.3.2 Chip Initialization..........................................................................................44 3.3.3 Bit Banging and UART Concepts.................................................................45 3.3.4 Software Interface for Accessing Hardware from a PC ...............................46 3.3.5 Code Generation..........................................................................................46 3.3.6 Implant Side Program Logic:........................................................................47 3.3.7 User-end Program Logic:.............................................................................49 3.3.8 Device Driver Portability...............................................................................52 3.4 INTEGRATED CIRCUIT SCHEMATIC......................................................................52 4 RESULTS AND DISCUSSION ......................................................... 57 4.1 XE1201A CONTROL REGISTERS INITIALIZATION: ................................................57 4.2 ERROR RATE IN DATA COMMUNICATION AND EFFICIENCY ...................................59 4.3 SENSOR VOLTAGE RANGE AND SENSITIVITY.......................................................62 4.3.1 Analog Sensors............................................................................................62 4.3.2 Temperature Sensor....................................................................................64 4.4 LABVIEW FRONT-END AND SCRIPT LANGUAGE DEVELOPMENT...........................65 4.5 BODY PHANTOM EXPERIMENT RESULTS.............................................................68