Signal-Adaptive Analog-to-Digital Converters for ULP Wearable and Implantable Medical Devices: A Survey

Signal-Adaptive Analog-to-Digital Converters for ULP Wearable and Implantable Medical Devices: A Survey

Nabi Sertac Artan
DOI: 10.4018/978-1-5225-5484-4.ch012
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The mission of this chapter is to introduce the reader the recent developments in the design of ultra-Low Power ADCs for Wearable and Implantable Medical Devices (WIMDs). The focus of this chapter will be on Signal-Adaptive Successive Approximation Register (SAR) ADC architectures and their derivatives, since the majority of the ULP medical devices rely on these architectures. The proposed chapter first provides an overview of the WIMDs, and electrophysiological signals. Then, basic SAR ADCs are introduced followed by the study of adaptive SAR ADCs. The chapter concludes with a brief summary of the other prevalent ADC architecture for WIMDs, namely the Level-Crossing ADCs.
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1. Introduction

There is a surge in wearable devices for physiological monitoring and treatment (Medtronic MiniMed insulin pump (Medtronic 2015), Second Sight Argus II Retinal Prosthesis (Second Sight 2015)) and for activity monitoring for healthy living (FitBit 2015). The wearable market is expected to have a 35% compound annual growth rate in the next five years (Danova 2015) and to reach to a global retail revenue of $53.2B by 2019 (Juniper Research 2014).

Similarly, implantable medical devices (IMDs) have become an indispensable option for patient monitoring and treatment, while their size has continuously shrunk. IMDs came a long way from the early pacemakers. For instance, the latest pacemakers such as Nanostim (St. Jude Medical 2015) can fit inside the heart eliminating the need for a surgical pocket, and can stimulate the heart without leads. There are over 4 million people with devices including pacemakers for managing cardiac rhythms worldwide, and 700,000 new pacemakers are implanted every year (Strickland 2013). Furthermore, modern IMDs offer new functionality for monitoring and treatment of various diseases and disorders ranging from Deep Brain Stimulation for Parkinson's disease with Medtronic ActiveRC (Medtronic 2015a) to weight loss treatment for obesity with EntroMedics Maestro System (EntroMedics 2015).

Together, Wearable/Implantable Medical Devices (WIMDs) provide exciting opportunities for significantly improving the health of the general population. On the other hand, the design and implementation of the WIMDs have unique engineering challenges.

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