An integrated circuit to enable electrodeposition and amperometric readout of sensing electrodes

This paper presents the design of an integrated circuit (IC) for (i) electrochemical deposition of sensor layers on the on-chip pad openings to form sensing electrodes, and (ii) amperometric readout of electrochemical sensors. The IC consists of two main circuit blocks: a Beta-multiplier based current reference for galvanostatic electrodeposition, and a switch-capacitor based amperometric readout circuit. The circuits are designed and simulated in a 180-nm CMOS process. The reference circuit generates a stable current of 99 nA with a temperature coefficient of 141 ppm/°C at best and 170 ppm/°C on average (across corners) over a supply voltage range of 1.2-2.4 V, and a line regulation of 0.7 %/V. The readout circuit measures current within pm 2 mu mathrmA with 99.9% linearity and a minimum integrated input-referred noise of 0.88 pA

An Integrated Circuit for Galvanostatic Electrodeposition of on-chip Electrochemical Sensors

This paper presents the design of an integrated circuit (IC) for (i) galvanostatic deposition of sensor layers on the on-chip pads, which serve as the sensor's base layer, and (ii) amperometric readout of electrochemical sensors. The system consists of three main circuit blocks: the electrochemical cell including a 4×4 electrode array, two Beta-multiplier based current generators and one pA-size current generator for galvanostatic electrodeposition, and a switch-capacitor based amperometric readout circuit for sensor current measurement. The circuits are designed and simulated in a 180-nm CMOS process. The three current reference circuits generate a stable current from 7.2 pA to 88 µA with low process, power supply voltage and temperature (PVT) sensitivity. The pA-size current generator has a temperature coefficient of 517.8 ppm/°C on average (across corners) in the range of 0 to 60°C. The line regulation is 4.4 %/V over a supply voltage range of 0.8-3 V. The feasibility of galvanostatic deposition on on-chip pads is validated by applying a fixed current of 300 nA to electrochemically deposit a gold layer on top of electrodes with nickel/zinc as the adhesive layer for gold. Successful deposition of gold was confirmed using optical microscope images of the on-chip electrodes

SpaceMan: Wireless SoC for concurrent potentiometry and amperometry

This work describes the implementation of SPACEMan, a wireless electrochemical system with concurrent potentiometric and amperometric sensing that can be utilised for saliva, sweat or point of care diagnostics. This system is designed with the vision of simpler interfaces for biofluid analysis. With a complete system-on-chip including electrochemical sensing, power management and data transmission, conventional interfaces like wirebonds will no longer be required in post-processing steps. The proposed architecture consists of a sensor front-end with four electrodes for concurrent amperometric and potentiometric sensing. This front-end outputs square wave signals mixed together with varying frequencies dependent on the sensed input, with the output type switchable with a state machine. A power management system consisting of a low dropout regulator (LDO) band gap reference (BGR), and a rectifier bridge is utilised for supplying power from an inductive link at 433MHz. Sensor data is transmitted wirelessly to a base station using LSK (Load-Shift Keying). The sensor front-end consumes 18µW, which the power management system more than adequately provides. The core area of the electronics without the coil is a conservative size of 0.41mm 2

Analogue circuit realisation of surface-confined redox reaction kinetics

The literature on voltammetry and electrochemical impedance spectroscopy (EIS) recognises the importance of using large-amplitude sinusoidal perturbations to better characterise electrochemical systems. To identify the parameters of a given reaction, various electrochemical models with different sets of values are simulated and compared against the experimental data to determine the best-fit set of parameters. However, the process of solving these nonlinear models is computationally expensive. This paper proposes analogue circuit elements for synthesising surface-confined electrochemical kinetics at the electrode interface. The resultant analogue model could be used as a solver to compute reaction parameters as well as a tracker for ideal biosensor behaviour. The performance of the analogue model was verified against numerical solutions to theoretical and experimental electrochemical models. Results show that the proposed analogue model has a high accuracy of at least 97% and a wide bandwidth of up to 2 kHz. The circuit consumed an average power of 9 μW

A 4-Wire Interface SoC for Shared Multi- Implant Power Transfer and Full-duplex Communication

This paper describes a novel system for recovering power and providing full-duplex communication over an AC-coupled 4-wire lead between active implantable devices. The target application requires a single Chest Device be connected to a Brain Implant consisting of multiple identical optrodes that record neural activity and provide closed loop optical stimulation. The interface is integrated within each optrode SoC allowing full-duplex and fully-differential communication based on Manchester encoding. The system features a head-to-chest uplink data rate (1.6 Mbps) that is higher than that of the chest-to-head downlink (100kbps) superimposed on a power carrier. On-chip power management provides an unregulated 5 V DC supply with up to 2.5 mA output current for stimulation, and a regulated 3.3 V with 60 dB PSRR for recording and logic circuits. The circuit has been implemented in a 0.35 μm CMOS technology, occupying 1.4 mm 2 silicon area, and requiring a 62.2 μA average current consumption

Study of Electrochemical Impedance of a Continuous Glucose Monitoring Sensor and its Correlation With Sensor Performance

In this article, we study the change in the sensitivity and the electrochemical impedance of continuous glucose monitoring sensors over time. In total, 28-day sensitivity and electrical impedance spectroscopy measurement results on four similar sensors are presented. The sensitivity of the sensor is observed to be related to its double-layer capacitance and charge-transfer resistance, based on results acquired from a sensor that showed substantial sensitivity drop. Two data clusters are extracted that relate the sensor sensitivity to its impedance before and after the sensitivity drops by more than 50%

Four-Wire Interface ASIC for a Multi-Implant Link

This paper describes an on-chip interface for recovering power and providing full-duplex communication over an AC-coupled 4-wire lead between active implantable devices. The target application requires two modules to be implanted in the brain (cortex) and upper chest; connected via a subcutaneous lead. The brain implant consists of multiple identical “optrodes” that facilitate a bidirectional neural interface (electrical recording and optical stimulation), and the chest implant contains the power source (battery) and processor module. The proposed interface is integrated within each optrode ASIC allowing full-duplex and fully-differential communication based on Manchester encoding. The system features a head-to-chest uplink data rate (up to 1.6 Mbps) that is higher than that of the chest-to-head downlink (100 kbps), which is superimposed on a power carrier. On-chip power management provides an unregulated 5-V dc supply with up to 2.5-mA output current for stimulation, and two regulated voltages (3.3 and 3 V) with 60-dB power supply rejection ratio for recording and logic circuits. The 4-wire ASIC has been implemented in a 0.35-μm CMOS technology, occupying a 1.5-mm 2 silicon area, and consumes a quiescent current of 91.2 μA. The system allows power transmission with measured efficiency of up to 66% from the chest to the brain implant. The downlink and uplink communication are successfully tested in a system with two optrodes and through a 4-wire implantable lead

Autonomous readout ASIC with 169dB input dynamic range for amperometric measurement

A readout circuit for the measurement of amperometric sensors is presented. The circuit consists of analog frontend (AFE) and an automatic gain adjustment circuit to tune the gain of the AFE according to the input current covering a wide dynamic range of 169dB and a minimum input referred noise of 44 fA. The circuit is implemented in 0.35 μm technology, consumes 5.83 mW from 3.3 V supply voltage and occupies 0.31 mm 2 silicon area

Autonomous readout ASIC with 169dB input dynamic range for amperometric measurement

A readout circuit for the measurement of amperometric sensors is presented. The circuit consists of analog frontend (AFE) and an automatic gain adjustment circuit to tune the gain of the AFE according to the input current covering a wide dynamic range of 169dB and a minimum input referred noise of 44 fA. The circuit is implemented in 0.35 μm technology, consumes 5.83 mW from 3.3 V supply voltage and occupies 0.31 mm 2 silicon area

DAPPER: a low Power, dual amperometric and potentiometric single-channel front end

DAPPER is a front end system capable of simultaneous amperometric and potentiometric sensing proposed for low-power multi-parameter analysis of bio-fluids such as saliva. The system consists of two oscillator circuits, generating a frequency relative to their sensed current and voltage signals. These signals are then mixed together to produce a single channel output that can be transmitted through backscattering (load-shift keying). The entire system consumes 40μW from a 1.4V supply. The linear ranges of potentiometry and amperometry circuits are 0.4V - 1V and 250pA - 5.6μA (87dB), and their input referred noise is 1.7μV and 44.6fA, respectively