Information processing and propagation in the central nervous system is mostly electrical in nature. At synapses, electrical signals cause the release of neurotransmitters like dopamine, glutamate etc., that are sensed by post-synaptic neurons resulting in signal propagation or inhibition. It can be very informative to monitor electrical and neurochemical signals simultaneously to understand the mechanisms underlying normal or abnormal brain function. We present an integrated system for the simultaneous wireless acquisition of neurophysiological and neurochemical activity. Applications of the system to neuroscience include monitoring EEG and glutamate in rat somatosensory cortex following global ischemia.
Effective compensation of phase noise in laser communication calls for fast, real-time, adaptive wavefront control. We
present an analog, continuous-time, high-speed VLSI (Very Large Scale Integration) controller implementing multi-dithering
perturbative gradient descent optimization of a direct measure of optical performance. The system applies parallel
sinusoidal perturbations to the wavefront over a range of frequencies, and performs parallel synchronous detection of
the metric signal to derive the gradient components over each frequency band. The system operates over a wide range
of frequencies, supporting applications of model-free adaptive optics extending from compensation of slow atmospheric
turbulence to compensation of fast random phase fluctuations in the actuators and laser amplifiers. The system has been
tested as a phase controller for a multiple laser beam wavefront propagating through a highly turbulent medium. The results
indicate a compensation bandwidth exceeding 300 kHz matching the turbulence bandwidth.
We demonstrate the coherent combining of three beams with a phase-locking controller using VLSI multi-dithering technique. Three fiber-coupled phase shifters are used to compensate phase distortions in the beam propagation path. The highest dither frequency in our system is ~70MHz. The achieved closed-loop compensation bandwidth of three beamlets is up to 100KHz.
Electroencephalograph (EEG) recording systems offer a versatile, noninvasive window on the brain's spatio-temporal activity for many neuroscience and clinical applications. Our research aims at improving the spatial
resolution and mobility of EEG recording by reducing the form factor, power drain and signal fanout of the
EEG acquisition node in a scalable sensor array architecture. We present such a node integrated onto a dimesized
circuit board that contains a sensor's complete signal processing front-end, including amplifier, filters,
and analog-to-digital conversion. A daisy-chain configuration between boards with bit-serial output reduces
the wiring needed. The circuit's low power consumption of 423 &mgr;W supports EEG systems with hundreds of
electrodes to operate from small batteries for many hours.
Coupling between the bit-serial output and the highly sensitive analog input due to dense integration of analog
and digital functions on the circuit board results in a deterministic noise component in the output, larger than
the intrinsic sensor and circuit noise. With software correction of this noise contribution, the system achieves
an input-referred noise of 0.277 &mgr;Vrms in the signal band of 1 to 100 Hz, comparable to the best medical-grade
systems in use. A chain of seven nodes using EEG dry electrodes created in micro-electrical-mechanical system
(MEMS) technology is demonstrated in a real-world setting.
KEYWORDS: Speckle, Image quality, Linear filtering, Analog electronics, Statistical analysis, Spectrum analysis, Adaptive optics, Very large scale integration, Digital filtering, Imaging systems
Real time wavefront control for adaptive laser communication and imaging system requires fast measurement of image quality.
Statistical analysis of speckle field provides effective image quality criteria for adaptive correction of phase-distorted images. We propose an analog continuous time VLSI (very-large-scale-integration) spectrum analysis chip to provide such a real time image quality measurement. The chip takes the signal sensed by a photo detector which is located in the speckle field as analog input and computes its spectrum distribution continuously. Experiment and analysis on distorted laser beam was conducted with the analog spectrum analysis chip. Target-in-the-loop system is under development to demonstrate the capability of real time adaptive imaging
The desire for persistent, long term surveillance and covertness places severe constraints on the power consumption of a sensor node. To achieve the desired endurance while minimizing the size of the node, it is imperative to use application-specific integrated circuits (ASICs) that deliver the required performance with maximal power efficiency while minimizing the amount of communication bandwidth needed. This paper reviews our ongoing effort to integrate several micropower devices for low-power wake-up detection, blind source separation and localization and pattern classification, and demonstrate the utility of the system in relevant surveillance applications. The capabilities of each module are presented in detail along with performance statistics measured during recent experiments.
Simultaneous mapping of multiple electrical or chemical properties of
neural activity facilitates understanding neurological phenomena and
their underlying mechanisms. We present a track-and-hold potentiostat
performing simultaneous acquisition of 16 independent channels of
current ranging five orders of magnitude in dynamic range over four
scales down to hundreds of picoamperes. Sampling rate ranges from DC
to 200KHz. The system features programmable current gain control,
configurable anti-aliasing log-domain filter, triggered current
integration and provides differential output ready for asynchronous
external analog-to-digital conversion over a compressed dynamic range.
We present system description, circuit implementation and experimental
results of real-time neurotransmitter concentration measurements from
the 16-channel prototype fabricated in a 1.2 micron CMOS process.
A wavefront sensing detector array is presented with capabilities suited towards high-order adaptive optics systems. The phase of the wavefront is sensed by modulating and synchronously sampling the fringes of a white light interferogram imaged onto the array. The nature of the modulation is characterized by a voltage signal, which is delivered as an input to the array. As a fringe moves across an individual detector, the null is sensed, triggering a sampling of the modulation signal. The sampled signal represents the phase of the wavefront and is held until the next null is sensed. The signal makes it possible to directly send commands to a deformable mirror to correct the phasefront. This chip is optically mapped such that each pixel in the array corresponds to an actuator on the deformable mirror. The array outputs both the photodetector current and the sampled modulation signal voltage from individual pixels by means of bit parallel row and column inputs. A prototype of this array has been fabricated in a 0.5μm CMOS process with 21 × 21 detectors, suitable for (circular) deformable mirrors with up to 349 actuators. Experimental results suggest refresh rates in excess of 3kHz are attainable. This wavefront sensor could greatly simplify the process of controlling a deformable mirror for many applications, thereby increasing refresh rates and improving sensitivity.
The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) currently has efforts internally and externally to develop advanced readout integrated circuits (ROICs) with on- chip processing capabilities. We have funded Raytheon Infrared Operations through a Dual Use Science and Technology program to develo and fabricate an advance ROIC with processing features including non-uniformity correction, extended charge handling, motion detection and edge enhancement. This advanced ROIC has been demonstrated through the successful development of the 'Adaptive Infrared Sensors' camera. Discussions of the circuit concepts and architecture of the 'AIRS' ROIC/FPA, as well as simulation results and test results of the camera is presented. Our internal investigations has resulted in an advanced readout design capable of real-time spatial and temporal filtering, to perform edge detection, edge enhancement, motion detection, and motion enhancement. The details of the circuit design, simulation results, as well as test data is presented.
We show that custom adaptive very large scale integrated (VLSI) circuit controllers can directly control commercially available wavefront phase correctors. These controllers achieve real-time wavefront compensation under conditions of strong intensity scintillations. Their control strategy is based on the optimization of a measurable performance index. Optimization is carried out using parallel perturbative stochastic gradient descent. We describe VLSI image-plane processors designed to compute a variety of application specific performance metrics in real-time.
We present a hybrid VLSI/Optical system for real-time adaptive phase distortion compensation. On-chip CMOS circuitry performs parallel perturbative stochastic gradient descent/ascent of an externally supplied optimization metric, e.g. a direct measure of image or laser beam quality. Our custom mixed-mode analog-digital VLSI system can directly control several adaptive optics elements such as micro-electromechanical mirrors, liquid crystal spatial light modulators and tilt mirrors. Here we use a tilt mirror and a MEMS mirror with 37 control parameters each of which is adjusted independently and in parallel to manipulate the wavefront phase profile. We present experimental results demonstrating successful operation for an adaptive laser- beam transmitter system. The parallel VLSI architecture is extendable to higher resolutions (N equals 103 to 106 parameters).
An adaptive laser beam focusing system using a 127 channel liquid crystal phase modulator is presented. The controller for the system is a circuit built with prototype VLSI chips that implement the stochastic parallel gradient descent algorithm. The controller is driven by a scalar laser beam quality metric and can run at the rate of 150 kHz. The system performance is characterized and a secondary control loop manipulating one of the algorithm parameters is experimentally investigated. The performance of the system is reported and performance improvements obtained by using the recent history of the beam quality metric to control an algorithm parameter is demonstrated.
The transfer matrix formalism, well known to describe the linear optical response of multilayered
structures, is extended to the plane wave response of multilayered structures with an arbitrary number of
Ken-type nonlinear layers, and including linear absorption too. It is shown that the dummy variable
technique, well known in the description of the nonlinear Fabry-Perot, can be extended for multilayered
structures. Several effects are highlighted for both superlattices and nonlinear interference filters.
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