Nima Soltani

Inductively-powered direct-coupled 64-channel chopper-stabilized epilepsy-responsive neurostimulator with digital offset cancellation and tri-band radio

An inductively powered 0.13μm CMOS neurostimulator SoC for intractable epilepsy treatment is presented. Digital offset cancellation yields a compact 0.018mm2 DC-coupled neural recording front-end. Input chopper stabilization is performed on all 64 channels resulting in a 4.2μVrms input-referred noise. A tri-band FSK/UWB radio provides a versatile transcutaneous interface. The inductive powering system includes a 20mm × 20mm 8-layer flexible receiver coil with 40% power transfer efficiency. In-vivo chronic epilepsy treatment experimental results show an average sensitivity and specificity of seizure detection of 87% and 95%, respectively, with over 76% of all seizures aborted.

Battery-less Tri-band-Radio Neuro-monitor and Responsive Neurostimulator for Diagnostics and Treatment of Neurological Disorders

A 0.13 μm CMOS system on a chip (SoC) for 64 channel neuroelectrical monitoring and responsive neurostimulation is presented. The direct-coupled chopper-stabilized neural recording front end rejects up to ±50 mV input dc offset using an in-channel digitally assisted feedback loop. It yields a compact 0.018 mm2 integration area and 4.2 μVrms integrated input-referred noise over 1 Hz to 1 kHz frequency range. A multiplying specific absorption rate (SAR) ADC in each channel calibrates channel-to-channel gain mismatch. A multicore low-power DSP performs synchrony-based neurological event detection and triggers a subset of 64 programmable current-mode stimulators for subsequent neuromodulation. Triple-band FSK/ultra-wideband (UWB) wireless transmitters communicate to receivers located at 10 cm to 10 m distance from the SoC with data rates from 1.2 to 45 Mbps. An inductive link that operates at 1.5 MHz, provides power and is also used to communicate commands to an on-chip ASK receiver. The chip occupies 16 mm2 while consuming 2.17 and 5.8 mW with UWB and FSK transmitters, respectively. Efficacy of the SoC is assessed using a rat model of temporal lobe epilepsy characterized by spontaneous seizures. It exhibits an average seizure detection sensitivity and specificity of 87% and 95%, respectively, with over 78% of all seizures aborted.

Battery-less modular responsive neurostimulator for prediction and abortion of epileptic seizures

An inductively-powered implantable microsystem for monitoring and treatment of intractable epilepsy is presented. The miniaturized system is comprised of two mini-boards and a power receiver coil. The first board hosts a 24-channel neurostimulator SoC developed in a 0.13μm CMOS technology and performs neural recording, electrical stimulation and on-chip digit l signal processing. The second board communicates recorded brain signals as well as signal processing results wirelessly, and generates different supply and bias voltages for the neurostimulator SoC and other external components. The multi-layer flexible coil receives inductively-transmitted power and sends it to the second board for power management. The system is sized at 2 × 2 × 0.7 cm3, weighs 6 grams, and is validated in control of chronic seizures in vivo in freely-moving rats.

27.3 All-wireless 64-channel 0.013mm 2 /ch closed-loop neurostimulator with rail-to-rail DC offset removal

Accurate capture and efficient control of neurological disorders such as epileptic seizures that often originate in multiple regions of the brain, requires neural interface microsystems with an ever-increasing need for higher channel counts. Addressing this demand within the limited energy and area of brain-implantable medical devices necessitates a search for new circuit architectures. In the conventional designs [1–5], the channel area is dominated by the bulky coupling capacitors and/or capacitor banks of the in-channel ADC, both unavoidable due to the channel architecture, and unscalable with CMOS technology. Additionally, channel power consumption, typically dominated by the LNA, cannot be reduced lower than a certain limit without sacrificing gain and/or noise performance. In this paper, we present a 64-channel wireless closed-loop neurostimulator with a compact and energy-efficient channel architecture that performs both amplification and digitization in a single ΔΣ-based neural ADC, while removing rail-to-rail input DC offset using a digital feedback loop. The channel area and power consumption depend only on the active components and switching frequency, respectively, making the design both technology- and frequency-scalable.

Inductively powered arbitrary-waveform adaptive-supply electro-optical neurostimulator

A hybrid current-mode and optogenetic miniature neurostimulating system is presented. The 16-channel electrical stimulator outputs arbitrary-waveform charge-balanced current-mode stimulation pulses with the amplitude ranging from 0.05mA to 10mA. To optimize power consumption, the supply voltage is automatically adjusted through an impedance monitoring feedback loop that gauges the minimum required headroom voltage. The 8-channel optogenetic stimulator reuses the arbitrary-waveform generation functions of the electrical stimulator. Each pulse-generator drives one LED with a maximum of 25mA. The LEDs are assembled within a custom-made 4×4 ECoG grid electrode array, which enables precise optical stimulation of neurons with a 300μm spatial resolution and simultaneous monitoring of the neural response by the ECoG electrode, at different distances of the stimulation site. The implantable system is a 3×2.5×1 cm3 stack of a receiver coil and two mini-boards. The power is received by a 32-layer flexible inductive coil and is regulated by the wireless communication board. The adaptive neurostimulator board boosts the regulated voltage up to the level set by the feedback loop with a maximum of 24V. The system also receives stimulation parameters wirelessly from the amplitude-shift-keyed power carrier. Both electrical and optogenetic stimulation results from chronic and acute in vivo rodent experiments are presented.

Tradeoffs between wireless communication and computation in closed-loop implantable devices

This paper discusses general tradeoffs between wireless communication and computation in closed-loop implantable medical devices for neurological applications. Closed-loop devices enable neural monitoring, automated diagnostics and treatment of neurological disorders. Several topologies for the loop a re discussed, including within the implant, as well as implemented with a wearable, handheld or stationary processor. Common wireless communication data rate and range requirements and algorithmic computational requirements are summarized. As a case study, a 0.13 μm CMOS neurostimulator SoC for closed-loop treatment of intractable epilepsy is presented. Its triple-band radio with a 1m 230Mbps pulse-radio, a 2m 46Mbps pulse-radio 2, and a 10m 1.2Mbps FSK radio provides a versatile transcutaneous interface. The in-implant processor has constrained computational resources which results in a limited detection performance — seizure detection sensitivity of 87%. A higher-performance signal processing algorithm implemented on a stationary device within a loop enhances the seizure detection performance which was improved to a sensitivity of 98% with three times fewer false alarms. This comes at the cost of an increased wireless transmitter power budget, if communicated directly. These results illustrate a fundamental tradeoff between the communication and computation in closed-loop electronic therapies for neurological disorders.

Low-Radiation Cellular Inductive Powering of Rodent Wireless Brain Interfaces: Methodology and Design Guide

This paper presents a general methodology of inductive power delivery in wireless chronic rodent electrophysiology applications. The focus is on such systems design considerations under the following key constraints: maximum power delivery under the allowable specific absorption rate (SAR), low cost and spatial scalability. The methodology includes inductive coil design considerations within a low-frequency ferrite-core-free power transfer link which includes a scalable coil-array power transmitter floor and a single-coil implanted or worn power receiver. A specific design example is presented that includes the concept of low-SAR cellular single-transmitter-coil powering through dynamic tracking of a magnet-less receiver spatial location. The transmitter coil instantaneous supply current is monitored using a small number of low-cost electronic components. A drop in its value indicates the proximity of the receiver due to the reflected impedance of the latter. Only the transmitter coil nearest to the receiver is activated. Operating at the low frequency of 1.5 MHz, the inductive powering floor delivers a maximum of 15.9 W below the IEEE C95 SAR limit, which is over three times greater than that in other recently reported designs. The power transfer efficiency of 39% and 13% at the nominal and maximum distances of 8 cm and 11 cm, respectively, is maintained.

An impedance-tracking battery-less arbitrary-waveform neurostimulator with load-adaptive 20V voltage compliance

A 4-channel wireless and battery-less neurostimulator with impedance-tracking power-adaptive voltage compliance is presented. The device houses a 10 mm2 0.35μm HV-CMOS SoC (system on a chip) that performs current-mode arbitrary-waveform stimulation with voltage compliance of up to 20 V. An on-chip mixed-signal controller together with a 3-bit charge-pump maintain supply voltage at its minimum required value, resulting in up to 68.5% saving in power. An 8-bit current DAC is implemented in each channel, which together with adjustable supply voltage yield a current range from 23 μA to 95 mA (100Ω load). The device receives both power and configuration commands wirelessly using a near-field inductive link. The neurostimulator SoC is wire-bonded on a 2×2 cm2 PCB. Additional rigid and flexible PCBs of the same size provide wireless command and power interface. The 3-board 2×2×0.7 cm3 stacked system weighs 6 grams.

Biofouling-Resistant Impedimetric Sensor for Array High-Resolution Extracellular Potassium Monitoring in the Brain

Extracellular potassium concentration, [K+]o, plays a fundamental role in the physiological functions of the brain. Studies investigating changes in [K+]o have predominantly relied upon glass capillary electrodes with K+-sensitive solution gradients for their measurements. However, such electrodes are unsuitable for taking spatio-temporal measurements and are limited by the surface area of their tips. We illustrate seizures invoked chemically and in optogenetically modified mice using blue light exposure while impedimetrically measuring the response. A sharp decrease of 1–2 mM in [K+]o before each spike has shown new physiological events not witnessed previously when measuring extracellular potassium concentrations during seizures in mice. We propose a novel approach that uses multichannel monolayer coated gold microelectrodes for in vivo spatio-temporal measurements of [K+]o in a mouse brain as an improvement to the conventional glass capillary electrode.

0.13μm CMOS 230Mbps 21pJ/b UWB-IR transmitter with 21.3% efficiency

An ultra-wide-band impulse-radio (UWB-IR) transmitter for low-energy implantable and wearable biomedical microsystems is presented. The transmitter provides a power-efficient high-data-rate wireless link within the 3-5 GHz band. It yields an overall power efficiency of 21.3% at data-rate of 230Mbps while consuming 21pJ per bit. The transmitted UWB pulse train is recovered at the receiver with less than 10-6 bit-error-rate (BER) measured at a distance of 1m without any pulse averaging. The chip is implemented in a 130nm CMOS technology and has an average power consumption of 3.7mW.