This paper presents an overview of the fundamentals and state of the-art in noninvasive physiological monitoring instrumentation with a focus on electrode and optrode interfaces to the body, and micropower-integrated circuit design for unobtrusive wearable applications. Since the electrode/optrode-body interface is a performance limiting factor in noninvasive monitoring systems, practical interface configurations are offered for biopotential acquisition, electrode-tissue impedance measurement, and optical biosignal sensing. A systematic approach to instrumentation amplifier (IA) design using CMOS transistors operating in weak inversion is shown to offer high energy and noise efficiency. Practical methodologies to obviate 1/f noise, counteract electrode offset drift, improve common-mode rejection ratio, and obtain subhertz high-pass cutoff are illustrated with a survey of the state-of-the-art IAs. Furthermore, fundamental principles and state-of-the-art technologies for electrode-tissue impedance measurement, photoplethysmography, functional near-infrared spectroscopy, and signal coding and quantization are reviewed, with additional guidelines for overall power management including wireless transmission. Examples are presented of practical dry-contact and noncontact cardiac, respiratory, muscle and brain monitoring systems, and their clinical applications.

Integrated Circuits and Electrode Interfaces for Noninvasive Physiological Monitoring

This paper presents an analog-to-digital converter (ADC) dedicated to neural recording systems. By using two continuous-time incremental sigma-delta ADCs in a pipeline configuration, the proposed ADC can achieve high-resolution without sacrificing the conversion rate. This two-step architecture is also power-efficient, as the resolution requirement for the incremental sigma-delta ADC in each step is significantly relaxed. To further enhance the power efficiency, a class-AB output stage and a dynamic summing comparator are used to implement the sigma-delta modulators. A prototype chip, designed and fabricated in a standard 0.18 $\mu{\rm m}$ CMOS process, validates the proposed ADC architecture. Measurement results show that the ADC achieves a peak signal-to-noise-plus-distortion ratio of 75.9 dB over a 4 kHz bandwidth; the power consumption is 34.8 $\mu{\rm W}$ , which corresponds to a figure-of-merit of 0.85 pJ/conv.

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A Power-Efficient Continuous-Time Incremental Sigma-Delta ADC for Neural Recording Systems

This paper presents an integrated circuit (IC) that merges integrated optical and temperature transducers, optical interface circuitry, and a near-field communication (NFC)-enabled digital, wireless readout for a fully passive implantable sensor platform to measure glucose in people with diabetes. A flip-chip mounted LED and monolithically integrated photodiodes serve as the transduction front-end to enable fluorescence readout. A wide-range programmable transimpedance amplifier adapts the sensor signals to the input of an 11-bit analog-to-digital converter digitizing the measurements. Measurement readout is enabled by means of wireless backscatter modulation to a remote NFC reader. The system is able to resolve current levels of less than 10 pA with a single fluorescent measurement energy consumption of less than 1 μJ. The wireless IC is fabricated in a 0.6-μm-CMOS process and utilizes a 13.56-MHz-based ISO15693 for passive wireless readout through a NFC interface. The IC is utilized as the core interface to a fluorescent, glucose transducer to enable a fully implantable sensor-based continuous glucose monitoring system.

An NFC-Enabled CMOS IC for a Wireless Fully Implantable Glucose Sensor

Wideband ( $\geq$ 10 MHz) continuous-time (CT) sigma-delta $(\Sigma\Delta)$ modulators generally use active-RC filters. On the other hand, Gm-C-filters avoid the need of a power-hungry driving stage due to their small loading. At the moment, the major challenge for designing Gm-C-based $\Sigma\Delta$ modulator is the narrow linear input range due to the nonlinear Gm amplifier, which leads to low SNDR. This work develops a nonlinearity compensation technique for Gm-C-based $\Sigma\Delta$ modulator. This technique designs a nonlinear feedback DAC which has matched V-I transfer curve as the first Gm amplifier (Gm1). As a result, the distortions of Gm1 are significantly suppressed at the modulator output. This method is prototyped in a 640 MS/s Gm-C-based $\Sigma\Delta$ modulator with 10 MHz signal bandwidth in a 0.18- $\mu{\rm m}$ CMOS process. With this technique, the linear input range of the modulator is greatly enlarged. Consequently, the peak SNDR of the modulator is improved by about 8 dB to 75 dB. This $>$ 12-bit ENOB is achieved for the first time for wide-band Gm-C-based $\Sigma\Delta$ modulators.

A 75 dB SNDR 10-MHz Signal Bandwidth Gm-C-Based Sigma-Delta Modulator With a Nonlinear Feedback Compensation Technique

Fluorescence biophotometry measurements require wide dynamic range (DR) and high-sensitivity laboratory apparatus. Indeed, it is often very challenging to accurately resolve the small fluorescence variations in presence of noise and high-background tissue autofluorescence. There is a great need for smaller detectors combining high linearity, high sensitivity, and high-energy efficiency. This paper presents a new biophotometry sensor merging two individual building blocks, namely a low-noise sensing front-end and a $2\text{nd}$ order continuous-time $\Sigma \Delta$ modulator (CTSDM), into a single module for enabling high-sensitivity and high energy-efficiency photo-sensing. In particular, a differential CMOS photodetector associated with a differential capacitive transimpedance amplifier-based sensing front-end is merged with an incremental $2\text{nd}$ order 1-bit CTSDM to achieve a large DR, low hardware complexity, and high-energy efficiency. The sensor leverages a hardware sharing strategy to simplify the implementation and reduce power consumption. The proposed CMOS biosensor is integrated within a miniature wireless head mountable prototype for enabling biophotometry with a single implantable fiber in the brain of live mice. The proposed biophotometry sensor is implemented in a 0.18- $\mu \text{m}$ CMOS technology, consuming $\text{41}\ \mu \text{W}$ from a 1.8- $\text{V}$ supply voltage, while achieving a peak dynamic range of $\text{86}\ \text{dB}$ over a 50- $\text{Hz}$ input bandwidth, a sensitivity of 24 mV/nW, and a minimum detectable current of 2.46- $pA_{\rm rms}$ at a 20- $\text{kS/s}$ sampling rate.

A Wireless Fiber Photometry System Based on a High-Precision CMOS Biosensor With Embedded Continuous-Time $\Sigma \Delta$ Modulation

This paper proposes a 3 rd order single-loop continuous-time incremental sigma-delta analogue-to-digital con- verter (ADC) for time-multiplexed signals. Incremental sigma- delta modulation is used to address medium to high resolution requirements of multi-channel applications, while a 3 rd order continuous-time implementation is investigated as an alternative for low-power solutions. A prototype of the proposed modulator, running at 320 kHz, has been fabricated in a 0.15-µm CMOS technology, while the synchronization circuitry to allow incre- mental operation was built on-board. Measurement results show that the ADC achieves 65.3 dB peak SNR, 64 dB peak SNDR and 68.2 dB dynamic range over a 2 kHz bandwidth. The modulator's power dissipation is 96 µW from a 1.6 V power supply. This translates into the best figure-of-merit when compared to recently published continuous-time alternatives, while being competitive with respect to state-of-the-art discrete-time counterparts. Index Terms—A/D conversion, incremental ADC, continuous-time.

A Low-Power CT Incremental 3rd Order ΣΔ ADC for Biosensor Applications.

The present invention relates to an implantable sensor configured to be implanted within the body of the subject and being configured to measure impedance within a body tissue of the subject resulting from an electrical current flowing through the body tissue, wherein the body tissue is sub-dermal or subcutaneous tissue of the subject. One pair of injection electrodes is configured for injection of electrical current into the body tissue and one pair of sensing electrodes is configured to detect the resulting voltage. A detector is operatively connected to the sensing electrodes and is configured to receive the voltage detected by the sensing electrodes, wherein the detector is configured to measure the impedance of the body tissue based on the voltage detected by the pair of sensing electrodes. A microcontroller is operatively connected to the detector and is configured to receive impedance signals from the detector and to provide control signals to the current signal output circuit and a powering and communication circuit including a coil configured to be powered by an electromagnetic field produced by an external coil.

Implantable Sensor and Method for Such Sensor

The present invention relates to a health monitoring system comprising an implantable sensor configured to measure impedance within a body tissue of the subject resulting from an electrical current flowing through said body tissue, wherein the body tissue is sub-dermal or subcutaneous tissue of said subject, the sensor including a powering and communication circuit having a coil configured to be powered by an electromagnetic field and to communicate with external devices. Further, the system comprises a reader module including a coil configured to produce the electromagnetic field for powering the powering and communication circuit and for communicating with the powering and communication circuit, a computing device comprising a display device, a processing device and at least one storage device, the computing device being configured to communicate with other devices via at least one wireless network and a monitoring engine for determining or monitoring at least one physiological parameter based on measured impedance, wherein the reader module and the computing device and the monitoring engine are configured to communicate with each other.

Saul Alejandro Rodriguez Duenas

Papers

A Low-Power CT Incremental 3rd Order ΣΔ ADC for Biosensor Applications.

Implantable Sensor and Method for Such Sensor

Health monitoring system