Al Thaddeus Avestruz

A 2

This paper describes a prototype micropower instrumentation amplifier intended for chronic sensing of neural field potentials (NFPs). NFPs represent the ensemble activity of thousands of neurons and code-useful information for both normal activity and disease states. NFPs are small - of the order of tens of muV- and reside at low bandwidths that make them susceptible to excess noise. Therefore, to ensure the highest fidelity of signal measurement for diagnostic analysis, the amplifier is chopper-stabilized to eliminate 1/f and popcorn noise. The circuit was prototyped in an 0.8 mum CMOS process and consumes under 2.0 muW from a 1.8 V supply. A noise floor of 0.98 muVrms was achieved over a bandwidth from 0.05 to 100 Hz; the noise-efficiency factor of 4.6 is one of the lowest published to date. A flexible on-chip high-pass filter is used to suppress front-end electrode offsets while maintaining relevant physiological data. The monolithic architect and micropower low-noise low-supply operation could help enable applications ranging from neuroprosthetics to seizure monitors that require a small form factor and battery operation. Although the focus of this paper is on neurophysiological sensing, the circuit architecture can be applied generally to micropower sensor interfaces that benefit from chopper stabilization.

\mu\hbox{W}

This paper describes an amplification and spectral processing IC for extracting key bioelectrical signals, or ldquobiomarkersrdquo, which are expressed in the brains field potentials. The intent is to explore using these biomarkers to drive prosthetic actuators or titrate therapy devices such as a deep-brain neurostimulator. The prototype IC uses 5 muW/channel to resolve signals on the order of 1 muVrms. The four channels on the device provide independent spectral analysis from DC to 1 kHz, with variable bandwidth and power filtering characteristics. The noise floor and flexible spectral processing support a broad range of potential applications including sleep staging, Parkinsons disease, detection of movement intention for neuroprosthesis, and detection of high frequency ldquofast ripplesrdquo for exploring seizure prediction. To fully demonstrate the ICs functionality, we include results from a prototype ldquoclosed-looprdquo neurostimulator implementing adaptive titration of therapy based on measured field potential activity.

100 nV/rtHz Chopper-Stabilized Instrumentation Amplifier for Chronic Measurement of Neural Field Potentials

Chronically implantable, closed-loop neuromodulation devices with concurrent sensing and stimulation hold promise for better understanding the nervous system and improving therapies for neurological disease. Concurrent sensing and stimulation are needed to maximize usable neural data, minimize time delays for closed-loop actuation, and investigate the instantaneous response to stimulation. Current systems lack concurrent sensing and stimulation primarily because of stimulation interference to neural signals of interest. While careful design of high performance amplifiers has proved useful to reduce disturbances in the system, stimulation continues to contaminate neural sensing due to biological effects like tissue-electrode impedance mismatch and constraints on stimulation parameters needed to deliver therapy. In this work we describe systematic methods to mitigate the effect of stimulation through a combination of sensing hardware, stimulation parameter selection, and classification algorithms that counter residual stimulation disturbances. To validate these methods we implemented and tested a completely implantable system for over one year in a large animal model of epilepsy. The system proved capable of measuring and detecting seizure activity in the hippocampus both during and after stimulation. Furthermore, we demonstrate an embedded algorithm that actuates neural modulation in response to seizure detection during stimulation, validating the capability to detect bioelectrical markers in the presence of therapy and titrate it appropriately. The capability to detect neural states in the presence of stimulation and optimally titrate therapy is a key innovation required for generalizing closed-loop neural systems for multiple disease states.

A 5

This paper presents a new strategy, diffusion charge redistribution (DCR), for balancing power among photovoltaic cells to increase energy extraction and to improve maximum power-point tracking (MPPT) efficiency under partial shading conditions. With DCR, testing and binning during cell manufacturing can be eliminated and significant cost savings can be achieved during production. The proposed technique performs power balancing by taking advantage of the intrinsic diffusion capacitance of the solar cells and requires no external passive components for energy storage, thereby minimizing power electronics cost and complexity. Strings balanced by this technique exhibit power versus current curves that are convex, which also greatly reduces the cost and complexity of the required MPPT algorithm.

\mu

A modified Z-source breaker topology is introduced to minimize the reflected fault current drawn from a source while retaining a common return ground path. A conventional Z-source breaker does not provide steady-state overload protection and can only guard against extremely large transient faults. The Z-source breaker can be designed for considerations affecting both rate of fault current rise and absolute fault current level, analogous in some respects to a “thermal-magnetic” breaker. The proposed manual tripping mechanism enables protection against both instantaneous current surges and longer-term over-current conditions. The fault operation intervals of the proposed Z-source breaker topologies are demonstrated in SPICE simulation.

W/Channel Spectral Analysis IC for Chronic Bidirectional Brain–Machine Interfaces

A modified Z-source breaker topology is introduced to minimize the reflected fault current drawn from a source while retaining a common return ground path. Conventional Z-source breaker topologies do not provide steady-state overload protection and can only guard against extremely large transient faults. The Z-source breaker can be designed for considerations affecting both rate of fault current rise and absolute fault current level, analogous in some respects to a thermal-magnetic breaker. Detailed analysis and design equations are presented to provide a framework for sizing components in the Z-source breaker topology. In addition, the proposed manual tripping mechanism enables protection against both instantaneous current surges and longer-term overcurrent conditions. The fault operation intervals of the proposed Z-source breaker topologies are both demonstrated in SPICE simulation and validated in experimental characterization.

Design and Validation of a Fully Implantable, Chronic, Closed-Loop Neuromodulation Device With Concurrent Sensing and Stimulation

We have developed a proximity sensor that can be integrated with a fluorescent lamp ballast. This sensor measures disturbances in the electric field around the lamp in order to detect the presence and motion of people. Range test data from our preliminary experiments showed detection ranges of 11 ft. between the lamp and the closest edge of a human target. The detector enables fine-grain occupancy measurements in spaces, promising to improve energy efficiency by reducing wasted lighting of unoccupied spaces.

Capacitor-Less Photovoltaic Cell-Level Power Balancing using Diffusion Charge Redistribution

This paper presents a new strategy, diffusion charge redistribution (DCR), for balancing power among photovoltaic cells to increase energy extraction and to improve maximum power point tracking (MPPT) efficiency under partial shading conditions. With DCR, testing and binning during cell manufacturing can be eliminated, and significant cost savings can be achieved during production. The proposed technique performs power balancing by taking advantage the intrinsic diffusion capacitance of the solar cells and requires no external passive components for energy storage, thereby minimizing power electronics cost and complexity. Strings balanced by this technique exhibit power versus current curves that are convex, which also greatly reduces the cost and complexity of the required MPPT algorithm.

Design of DC system protection

This paper presents a retrofit system that exploits a fluorescent lamps own stray electric fields for capacitive sensing. Occupancy detection for demand-side energy management is a key application. The experimental system demonstrates a detection range of 10 ft. between the lamp and the nearest edge of the occupant. A full system model is presented including the simulation of a lumped element capacitive model. The full system model is validated against experimental data.

Analysis and Design of DC System Protection Using Z-Source Circuit Breaker

We have investigated a method to regulate the voltages in the secondary windings of an induction machine stator with multiple windings. By introducing one or more triple-n harmonics in a three-phase machine, the rectified output voltage of one or more grounded-wye windings can be controlled and regulated. Voltage regulation is achieved through triple-n harmonic current injection, so there is no net torque on the rotor, decoupling voltage regulation from drive. We demonstrate and analyze voltage control in a custom wound induction machine by the addition of third harmonic to the inverter drive waveform. The rectified output voltage depends not only on the amplitude, but also on the phase of the third harmonic. The ability to orthogonally control voltage is particularly important in applications where the machine is used as a generator, motor and/or power converter at the same time