A four-quadrant switched capacitor DC-DC convertor enabling power-efficient lab-grade potentiostats

This paper presents a low-power potentiostat based on a four-quadrant switched capacitor DC-DC convertor for use in lab applications. The gearbox convertor achieves a compliance voltage of ±2.5V. Through the use of frequency scaling, the convertor features output currents in the range of 1µA to 1mA, outclassing other state-of-the-art power efficient potentiostats. A hysteretic control loop and a seperate hysteretic comparator allow the potentiostat to be used for both voltammetric and ampere-metric experiments. Simulations demonstrate a peak efficiency of 87%, and a competitive overall efficiency. The system is designed and simulated in a 0.35µm process

45-nm SOI CMOS Bluetooth Electrochemical Sensor for Continuous Glucose Monitoring

Due to increasing rates of diabetes, non-invasive glucose monitoring systems will become critical to improving health outcomes for an increasing patient population. Bluetooth integration for such a system has been previously unattainable due to the prohibitive energy consumption. However, enabling Bluetooth allows for widespread adoption due to the ubiquity of Bluetooth-enabled mobile devices. The objective of this thesis is to demonstrate the feasibility of a Bluetooth-based energy-harvesting glucose sensor for contact-lens integration using 45~nm silicon-on-insulator (SOI) complementary metal-oxide-semiconductor (CMOS) technology. The proposed glucose monitoring system includes a Bluetooth transmitter implemented as a two-point closed loop PLL modulator, a sensor potentiostat, and a 1st-order incremental delta-sigma analog-to-digital converter (IADC). This work details the complete system design including derivation of top-level specifications such as glucose sensing range, Bluetooth protocol timing, energy consumption, and circuit specifications such as carrier frequency range, output power, phase-noise performance, stability, resolution, signal-to-noise ratio, and power consumption. Three test chips were designed to prototype the system, and two of these were experimentally verified. Chip 1 includes a partial implementation of a phase-locked-loop (PLL) which includes a voltage-controlled-oscillator (VCO), frequency divider, and phase-frequency detector (PFD). Chip 2 includes the design of the sensor potentiostat and IADC. Finally, Chip 3 combines the circuitry of Chip 1 and Chip 2, along with a charge-pump, loop-filter and power amplifier to complete the system. Chip 1 DC power consumption was measured to be 204.8~$\mu$W, while oscillating at 2.441 GHz with an output power $P_{out}$ of -35.8 dBm, phase noise at 1 MHz offset $L(1\text{ MHz})$ of -108.5 dBc/Hz, and an oscillator figure of merit (FOM) of 183.44dB. Chip 2 achieves a total DC power consumption of 5.75~$\mu$W. The system has a dynamic range of 0.15~nA -- 100~nA at 10-bit resolution. The integral non-linearity (INL) and differential non-linearity (DNL) of the IADC were measured to be -6~LSB/$\pm$0.3~LSB respectively with a conversion time of 65.56~ms. This work achieves the best duty-cycled DC power consumption compared to similar glucose monitoring systems, while providing sufficient performance and range using Bluetooth

Integrated Electronics to Control and Readout Electrochemical Biosensors for Implantable Applications

Biosensors can effectively be used to monitor multiple metabolites such as glucose, lactate, ATP and drugs in the human body. Continuous monitoring of these metabolites is essential for patients with chronic or critical conditions. Moreover, this can be used to tune the dosage of a drug for each individual patient, in order to achieve personalized therapy. Implantable medical devices (IMDs) based on biosensors are emerging as a valid alternative for blood tests in laboratories. They can provide continuous monitoring while reduce the test costs. The potentiostat plays a fundamental role in modern biosensors. A potentiostat is an electronic device that controls the electrochemical cell, using three electrodes, and runs the electrochemical measurement. In particular the IMDs require a low-power, fully-integrated, and autonomous potentiostats to control and readout the biosensors. This thesis describes two integrated circuits (ICs) to control and readout multi-target biosensors: LOPHIC and ARIC. They enable chronoamperometry and cyclic voltammetrymeasurements and consume sub-mW power. The design, implementation, characterisation, and validation with biosensors are presented for each IC. To support the calibration of the biosensors with environmental parameters, ARIC includes circuitry to measure the pHand temperature of the analyte through an Iridiumoxide pH sensor and an off-chip resistor-temperature detector (RTD). In particular, novel circuits to convert resistor value into digital are designed for RTD readout. ARIC is integrated into two IMDs aimed for health-care monitoring and personalized therapy. The control and readout of the embedded sensor arrays have been successfully achieved, thanks to ARIC, and validated for glucose and paracetamol measurements while it is remotely powered through an inductive link. To ensure the security and privacy of IMDs, a lightweight cryptographic system (LCS) is presented. This is the first ASIC implementation of a cryptosystem for IMDs, and is integrated into ARIC. The resulting system provides a unique and fundamental capability by immediately encrypting and signing the sensor data upon its creation within the body. Nano-structures such as Carbon nanotubes have been widely used to improve the sensitivity of the biosensors. However, in most of the cases, they introduce more noise into the measurements and produce a large background current. In this thesis the noise of the sensors incorporating CNTs is studied for the first time. The effect of CNTs as well as sensor geometry on the signal to noise ratio of the sensors is investigated experimentally. To remove the background current of the sensors, a differential readout scheme has been proposed. In particular, a novel differential readout IC is designed and implemented that measures inputcurrents within a wide dynamic range and produces a digital output that corresponds to the -informative- redox current of the biosensor

Integrated circuit & system design for concurrent amperometric and potentiometric wireless electrochemical sensing

Complementary Metal-Oxide-Semiconductor (CMOS) biosensor platforms have steadily grown in healthcare and commerial applications. This technology has shown potential in the field of commercial wearable technology, where CMOS sensors aid the development of miniaturised sensors for an improved cost of production and response time. The possibility of utilising wireless power and data transmission techniques for CMOS also allows for the monolithic integration of the communication, power and sensing onto a single chip, which greatly simplifies the post-processing and improves the efficiency of data collection. The ability to concurrently utilise potentiometry and amperometry as an electrochemical technique is explored in this thesis. Potentiometry and amperometry are two of the most common transduction mechanisms for electrochemistry, with their own advantages and disadvantages. Concurrently applying both techniques will allow for real-time calibration of background pH and for improved accuracy of readings. To date, developing circuits for concurrently sensing potentiometry and amperometry has not been explored in the literature. This thesis investigates the possibility of utilising CMOS sensors for wireless potentiometric and amperometric electrochemical sensing. To start with, a review of potentiometry and amperometry is evaluated to understand the key factors behind their operation. A new configuration is proposed whereby the reference electrode for both electrochemistry techniques are shared. This configuration is then compared to both the original configurations to determine any differences in the sensing accuracy through a novel experiment that utilises hydrogen peroxide as a measurement analyte. The feasibility of the configuration with the shared reference electrode is proven and utilised as the basis of the electrochemical configuration for the front end circuits. A unique front-end circuit named DAPPER is developed for the shared reference electrode topology. A review of existing architectures for potentiometry and amperometry is evaluated, with a specific focus on low power consumption for wireless applications. In addition, both the electrochemical sensing outputs are mixed into a single output data channel for use with a near-field communication (NFC). This mixing technique is also further analysed in this thesis to understand the errors arising due to various factors. The system is fabricated on TSMC 180nm technology and consumes 28µW. It measures a linear input current range from 250pA - 0.1µW, and an input voltage range of 0.4V - 1V. This circuit is tested and verified for both electrical and electrochemical tests to showcase its feasibility for concurrent measurements. This thesis then provides the integration of wireless blocks into the system for wireless powering and data transmission. This is done through the design of a circuit named SPACEMAN that consists of the concurrent sensing front-end, wireless power blocks, data transmission, as well as a state machine that allows for the circuit to switch between modes: potentiometry only, amperometry only, concurrent sensing and none. The states are switched through re-booting the circuit. The core size of the electronics is 0.41mm² without the coil. The circuit’s wireless powering and data transmission is tested and verified through the use of an external transmitter and a connected printed circuit board (PCB) coil. Finally, the future direction for ongoing work to proceed towards a fully monolithic electrochemical technique is discussed through the next development of a fully integrated coil-on-CMOS system, on-chip electrodes with the electroplating and microfludics, the development of an external transmitter for powering the device and a test platform. The contributions of this thesis aim to formulate a use for wireless electrochemical sensors capable of concurrent measurements for use in wearable devices.Open Acces