UBC Theses and Dissertations
Ultra-low-power event-driven radio system for miniaturized biomedical implants Cai, Mengye
The aggressive scaling of the CMOS technologies has made it possible to implement denser, cheaper, higher performance and lower power integrated circuits (ICs) for a widespread of applications. Among these applications in various implantable medical devices (IMDs) such as cochlear implants, capsule endoscopy, brain-machine interface, and smart stents, telemonitoring and wireless communication are key functions. The radio-frequency (RF) communication systems for IMDs differ from conventional data-driven radios in various aspects including form factor, power consumption, communication range, and operation manner. The focus of this thesis is on exploring novel circuit- and system-level design techniques for monolithic CMOS wireless event-driven radios intended for miniaturized biomedical implants. To fulfill the stringent power requirement, conventionally various forms of envelope-detection-based receivers are used. However, such receivers suffer from inferior sensitivity and also need calibration or external components, which are not amenable solutions for IMDs. To address these issues, a crystal-less receiver that employs a programmable envelope detector to provide a better trade-off between sensitivity and power consumption is presented. Furthermore, a double-mixing receiver is robust to process, supply voltage and ambient temperature (PVT) variations. By suppressing flicker noise and DC offsets, the proposed architecture while achieving an improved sensitivity eliminates the need for external components and calibration. There are typically three wireless links existing in an implantable radio system, the uplink, the downlink, and the power link. In this work, the up- and down-stream datalinks are realized by exploiting 915 MHz frequency band using time division duplexing (TDD) that is manipulated by a smart control module, while remote power link is realized in the 2.4 GHz band. Without any external components and calibration overhead, the radio is also robust to PVT variations, leading to a low-cost and highly integrated wireless node. To confirm the validity of the proposed technique, proof-of-concept prototypes have been designed and fabricated. All prototype circuits have been implemented in CMOS technology and have been successfully evaluated. The applications of proposed techniques are not limited to IMDs and they can also be used in other applications where energy resources are constrained and/or low power operation with miniaturized size are required.
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