CMOS Interfaces for Internet-of-Wearables Electrochemical Sensors: Trends and Challenges

Abstract

Smart wearables, among immediate future IoT devices, are creating a huge and fast growing market that will encompass all of the next decade by merging the user with the Cloud in a easy and natural way. Biological fluids, such as sweat, tears, saliva and urine offer the possibility to access molecular-level dynamics of the body in a non-invasive way and in real time, disclosing a wide range of applications: from sports tracking to military enhancement, from healthcare to safety at work, from body hacking to augmented social interactions. The term Internet of Wearables (IoW) is coined here to describe IoT devices composed by flexible smart transducers conformed around the human body and able to communicate wirelessly. In addition the biochemical transducer, an IoW-ready sensor must include a paired electronic interface, which should implement specific stimulation/acquisition cycles while being extremely compact and drain power in the microwatts range. Development of an effective readout interface is a key element for the success of an IoW device and application. This review focuses on the latest efforts in the field of Complementary Metal–Oxide–Semiconductor (CMOS) interfaces for electrochemical sensors, and analyses them under the light of the challenges of the IoW: cost, portability, integrability and connectivity.

A Low-Power CMOS Bandgap Voltage Reference for Supply Voltages Down to 0.5 V

“…In a triple-well process (or p-well), a source-body connection would be allowed, making the V re f of the circuits in Figures 1b and 3a perfectly equivalent. This condition is clearly not essential, since the sum of a PTAT and a CTAT term is present in the expression of V re f given in Equation (6). More interestingly, it is possible to demonstrate that, imposing an R 1 /R T ratio that nulls the V re f temperature derivative at T = T 0 , the expression of the reference voltage of the proposed BG core at T = T 0 is the same as Equation ( 5) regardless of the presence of a body-source connection.…”

“…In the era of the Internet of Things (IoT), the development of nonintrusive wearable biomedical devices is stimulating research in many different fields, including that of integrated electronic circuits [1][2][3][4]. The need to monitor important vital parameters during the normal daily activities of humans has motivated the design of autonomous wearable devices capable of performing chemical-physical analysis of body fluids such as sweat, tears, and urine [5][6][7]. One of the main challenges posed by these devices is related to the availability of very low power budgets, typically provided by small batteries and/or energy harvesters.…”

Design of a Capacitance-to-Digital Converter Based on Iterative Delay-Chain Discharge in 180 nm CMOS Technology

“…The target capacitive sensor considered in this work derives from the wearable platform for sweat-rate sensing sketched in Figure 1 . This device is intended to be used for activity tracking in sport applications, and it consists of (i) a flexible printed-circuit board (FPCB) layer, typically a polyimide film; (ii) a decorated elastometer layer, typically polydimethylsiloxane (PDMS), and (iii) an application-specific integrated circuit (ASIC) [ 18 , 19 , 20 , 21 ]. The fluidic pathway is then formed by sealing the two layers together and providing an inlet and an outlet, facing, respectively, the skin and the air.…”

A 15-μW 105-dB 1.8-Vpp Potentiostatic Delta-Sigma Modulator for Wearable Electrochemical Transducers in 65-nm CMOS Technology

“…The embodiment of such wearable devices need to deal with conformability, flexibility, durability, data integrity, light weight, and low production cost. For this reason, specific design techniques towards low-cost and low-power CMOS circuit interfaces for electrochemical sensors are experimenting a growing interest [4]. Providing intelligence to transducers allows for sensory data acquisition, processing and communication on single silicon chip attached to transducer low-cost substrates.…”