Abraham Akinin

Integrated Circuits and Electrode Interfaces for Noninvasive Physiological Monitoring

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.

Silicon-Integrated High-Density Electrocortical Interfaces

Recent demand and initiatives in brain research have driven significant interest toward developing chronically implantable neural interface systems with high spatiotemporal resolution and spatial coverage extending to the whole brain. Electroencephalography-based systems are noninvasive and cost efficient in monitoring neural activity across the brain, but suffer from fundamental limitations in spatiotemporal resolution. On the other hand, neural spike and local field potential (LFP) monitoring with penetrating electrodes offer higher resolution, but are highly invasive and inadequate for long-term use in humans due to unreliability in long-term data recording and risk for infection and inflammation. Alternatively, electrocorticography (ECoG) promises a minimally invasive, chronically implantable neural interface with resolution and spatial coverage capabilities that, with future technology scaling, may meet the needs of recently proposed brain initiatives. In this paper, we discuss the challenges and state-of-the-art technologies that are enabling next-generation fully implantable high-density ECoG interfaces, including details on electrodes, data acquisition front-ends, stimulation drivers, and circuits and antennas for wireless communications and power delivery. Along with state-of-the-art implantable ECoG interface systems, we introduce a modular ECoG system concept based on a fully encapsulated neural interfacing acquisition chip (ENIAC). Multiple ENIACs can be placed across the cortical surface, enabling dense coverage over wide area with high spatiotemporal resolution. The circuit and system level details of ENIAC are presented, along with measurement results.

A 144MHz integrated resonant regulating rectifier with hybrid pulse modulation

This paper presents a CMOS fully-integrated resonant regulating rectifier (IR³) for inductive power telemetry in implantable devices. Employing PWM and PFM feedback, the IR³ achieves 1.87% of ΔV_DD/V_DD ratio despite a tenfold change in load with a 1nF decoupling capacitor. At 1V regulation of a 100μW load from a 144MHz RF input, the measured voltage conversion efficiency is greater than 92% at under 5.2mV_pp ripple and 54% power conversion efficiency. Implemented in 180nm SOI CMOS, the IR³ circuit occupies 0.078mm² active area.

Towards high-resolution retinal prostheses with direct optical addressing and inductive telemetry.

OBJECTIVE Despite considerable advances in retinal prostheses over the last two decades, the resolution of restored vision has remained severely limited, well below the 20/200 acuity threshold of blindness. Towards drastic improvements in spatial resolution, we present a scalable architecture for retinal prostheses in which each stimulation electrode is directly activated by incident light and powered by a common voltage pulse transferred over a single wireless inductive link. APPROACH The hybrid optical addressability and electronic powering scheme provides separate spatial and temporal control over stimulation, and further provides optoelectronic gain for substantially lower light intensity thresholds than other optically addressed retinal prostheses using passive microphotodiode arrays. The architecture permits the use of high-density electrode arrays with ultra-high photosensitive silicon nanowires, obviating the need for excessive wiring and high-throughput data telemetry. Instead, the single inductive link drives the entire array of electrodes through two wires and provides external control over waveform parameters for common voltage stimulation. MAIN RESULTS A complete system comprising inductive telemetry link, stimulation pulse demodulator, charge-balancing series capacitor, and nanowire-based electrode device is integrated and validated ex vivo on rat retina tissue. SIGNIFICANCE Measurements demonstrate control over retinal neural activity both by light and electrical bias, validating the feasibility of the proposed architecture and its system components as an important first step towards a high-resolution optically addressed retinal prosthesis.

A fully integrated 144 MHz wireless-power-receiver-on-chip with an adaptive buck-boost regulating rectifier and low-loss H-Tree signal distribution

An adaptive buck-boost resonant regulating rectifier (B²R³) with an integrated on-chip coil and low-loss H-Tree power/signal distribution is presented for efficient and robust wireless power transfer (WPT) over a wide range of input and load conditions. The B²R³ integrated on a 9 mm² chip powers integrated neural interfacing circuits as a load, with a TX-load power conversion efficiency of 2.64 % at 10 mm distance, resulting in a WPT system efficiency FoM of 102.

Data assimilation of membrane dynamics and channel kinetics with a neuromorphic integrated circuit

Techniques of data assimilation (DA) for parameter identification and forecasting in complex dynamical systems offer promising tools for the analysis of neural data and inference of neural function. Here we present experiments using DA to characterize the dynamics of a neuromorphic very large-scale integrated (VLSI) circuit emulating membrane dynamics and channel kinetics in a network of 4 generalized Hodgkin-Huxley neurons coupled through 12 conductance-based chemical synapses. The analog VLSI chip, NeuroDyn, features 384 digitally programmable parameters specifying for all neurons and synapses reversal potentials, conductances, and spline-regressed voltage dependence profile of opening and closing rates of the gating variables. In a set of experiments, we conducted DA on the membrane potentials of neurons recorded on the chip under current injection according to the model structure upon which the chip was designed and the known current input sequence, to arrive at the programmed parameters save for model errors due to analog imperfections in the chip fabrication. In a related set of experiments we extended the DA procedure to map songbird neural dynamics onto the chip by identifying and programming parameters extracted using DA from intracellular neural recordings. Application of the chip to neurological data may help to understand the effects of neuromodulators or neurodegenerative diseases on ion channel kinetics, and may further provide insights into the relationship between molecular properties of neurons and the emergence of different spike patterns or different brain behaviors.

A CMOS 4-channel MIMO baseband receiver with 65dB harmonic rejection over 48MHz and 50dB spatial signal separation over 3MHz at 1.3mW

A CMOS integrated 4-channel capacitive harmonic rejection baseband receiver and 4×4 MIMO analog core spatial filter demonstrate >65dB harmonic folding rejection over 48MHz, and >48.5dB signal separation across 3MHz baseband. The 65nm CMOS IC occupies 3.27mm2 active area and consumes 0.67mW-1.28mW.

Visual evoked potential characterization of rabbit animal model for retinal prosthesis research

Visual evoked potentials (VEP) are used to confirm the function of prosthetic devices designed to stimulate retinas with damaged photoreceptors in vivo. In this work, we focus on methods and experimental consideration for recording visual evoked potential in rabbit models and assesses the use for retinal prosthesis research. We compare both invasive and noninvasive methods for recording VEPs, the response of the rabbit retina to various light wavelengths and intensities, focal vs. full field stimulation, and the effect of light bleaching on the retinal response.

Design of miniaturized wireless power receivers for mm-sized implants

Advances in free-floating miniature medical implants promise to offer greater effectiveness, safety, endurance, and robustness than todays prevailing medical implants. Wireless power transfer (WPT) is key to miniaturized implants by eliminating the need for bulky batteries. This paper reviews design strategies for WPT with mm-sized implants focusing on resonant electromagnetic and ultrasonic transmission. While ultrasonic WPT offers shorter wavelengths for sub-mm implants, electromagnetic WPT above 100 MHz offers superior power transfer and conversion efficiency owing to better impedance matching through inhomogeneous tissue. Electromagnetic WPT also allows for fully integrating the entire wireless power receiver system with an on-chip coil. Attaining high power transfer efficiency requires careful design of the integrated coil geometry for high quality factor as well as loop-free power and signal distribution routing to avoid eddy currents. Regulating rectifiers have improved power and voltage conversion efficiency by combining the two RF to DC conversion steps into a single process. Example designs of regulating rectifiers for fully integrated wireless power receivers are presented.

A 16-channel wireless neural interfacing SoC with RF-powered energy-replenishing adiabatic stimulation

This paper presents a fully-integrated 16-channel wireless neural interfacing SoC that employs an adiabatic stimulator powered directly from a 190-MHz on-chip antenna to eliminate bulky external components while simultaneously avoiding rectifier and regulator losses. Using a charge replenishing architecture, the stimulator outputs up to 145-μA, while achieving a 63.1% charge replenishing ratio and a stimulation efficiency factor of 6.0. Analog front-ends (AFEs) and telemetry circuitry are also included.