Milutin Stanacevic

VLSI Potentiostat Array With Oversampling Gain Modulation for Wide-Range Neurotransmitter Sensing

A 16-channel current-measuring very large-scale integration (VLSI) sensor array system for highly sensitive electrochemical detection of electroactive neurotransmiters like dopamine and nitric-oxide is presented. Each channel embeds a current integrating potentiostat within a switched-capacitor first-order single-bit delta-sigma modulator implementing an incremental analog-to-digital converter. The duty-cycle modulation of current feedback in the delta-sigma loop together with variable oversampling ratio provide a programmable digital range selection of the input current spanning over six orders of magnitude from picoamperes to microamperes. The array offers 100-fA input current sensitivity at 3.4-muW power consumption per channel. The operation of the 3 mm times3 mm chip fabricated in 0.5-mum CMOS technology is demonstrated with real-time multichannel acquisition of neurotransmitter concentration

16-Channel Integrated Potentiostat for Distributed Neurochemical Sensing

We present the architecture and VLSI circuit implementation of a BiCMOS potentiostat bank for monitoring neurotransmitter concentration on a screen-printed carbon electrode array. The potentiostat performs simultaneous acquisition of bidirectional reduction-oxidation currents proportional to neurotransmitter concentration on 16 independent channels at controlled redox potentials. Programmable current gain control yields over 100-dB cross-scale dynamic range with 46-pA input-referred rms noise over 12-kHz bandwidth. The cutoff frequency of a second-order log-domain anti-aliasing filter ranges from 50 Hz to 400 kHz. Track-and-hold current integration is triggered at the sampling rate between dc and 200 kHz. A 2.25-mmtimes2.25-mm prototype was fabricated in a 1.2-mum VLSI technology and dissipates 12.5 mW. Chronoamperometry dopamine concentration measurements results are given. Other types of neurotransmitters can be selected by adjusting the redox potential on the electrodes and the surface properties of the sensor coating

Nanosensor and Breath Analyzer for Ammonia Detection in Exhaled Human Breath

The detection and monitoring of gases in exhaled human breath up to date has been limited by the lack of appropriate materials and technologies which could rapidly and selectively identify the presence and monitor the concentration of trace levels of specific analytes-biomarkers. We present a metal oxide-based nanosensor that is highly specific to ammonia gas in breath-simulating environments at low part-per-billion concentrations. The design of a handheld breath analyzer for gas detection in exhaled human breath is described. Semiconducting ceramics are presented as suitable sensor materials for easy and affordable noninvasive diagnostics.

Micropower gradient flow acoustic localizer

A micropower mixed-signal system-on-chip for three-dimensional localization of a broad-band acoustic source is presented. Direction cosines of the source are obtained by relating spatial and temporal differentials in the acoustic traveling wave field acquired across four coplanar microphones at subwavelength spacing. Correlated double sampling and least-squares adaptive cancellation of common-mode leakthrough in the switched-capacitor analog differentials boost localization accuracy at very low aperture. A second stage of mixed-signal least-squares adaptation directly produces digital estimates of the direction cosines. The 3mm /spl times/ 3mm chip in 0.5-/spl mu/m CMOS technology quantizes signal delays with 250-ns resolution at 16-kHz sampling rate, and dissipates 54 /spl mu/W power from a 3-V supply. Field tests of the processor with acoustic enclosure demonstrated its utility and endurance in tracking ground and airborne vehicles. Applications include acoustic surveillance, interactive multimedia, and intelligent hearing aids.

Integrated potentiostat for neurotransmitter sensing

We have presented a chemical analysis paradigm for neurochemical studies, as opposed to the traditional electrophysiological regime. We described electrochemical analysis and the instrumentation involved in doing such analysis. The article presents the design and characterization of a 16-channel, high-sensitivity, wide-range VLSI potentiostat. We demonstrate the use of this potentiostat in real-time in vitro monitoring of the neurotransmitter dopamine.

Blind broadband source localization and separation in miniature sensor arrays

We study the ability of a sensor array to blindly separate and localize broadband traveling waves impinging on the array, with additive sensor noise. We consider arrays smaller than the shortest wavelength in the sources, such as MEMS acoustic arrays or VLSI arrays of RF receivers. A series expansion about the center of the array of the time-delayed signals emanating from the sources reduces the problem of separating and localizing the delayed sources to that of separating instantaneous signal mixtures using conventional tools of Independent Component Analysis. The covariance of the noise in the estimated sources is expressed in terms of the covariance of the sensor noise and the angular direction of the sources. Physical simulations demonstrate separation and localization of three non-coplanar speech sources using a planar array of four sensors within a 1 mm radius.

Wide-range, picoampere-sensitivity multichannel VLSI potentiostat for neurotransmitter sensing

Neurotransmitter sensing is critical in studying nervous pathways and neurological disorders. A 16-channel current-measuring VLSI potentiostat with multiple ranges from picoamperes to microamperes is presented for electrochemical detection of electroactive neurotransmitters like dopamine, nitric oxide etc. The analog-to-digital converter design employs a current-mode, first-order single-bit delta-sigma modulator architecture with a two-stage, digitally reconfigurable oversampling ratio for ranging the conversion scale. An integrated prototype is fabricated in CMOS technology, and experimentally characterized. Real-time multi-channel acquisition of dopamine concentration in vitro is performed with a microfabricated sensor array.

Mixed-signal real-time adaptive blind source separation

A mixed-signal adaptive VLSI architecture for real-time blind separation of linear source mixtures is presented. The architecture is digitally reconfigurable and implements a general class of independent component analysis (ICA) update rules in common outer-product form. In conjunction with gradient flow, a technique for converting wave sources into equivalent linear instantaneous mixtures by observing spatial and temporal derivatives of the field over a miniature array, the ICA architecture allows to separate and localize multiple acoustic sources in the acoustic scene. Experimental results from VLSI implementation of the ICA architecture demonstrate 30 dB separation of two mixtures of two speech signals.

Gradient flow adaptive beamforming and signal separation in a miniature microphone array

Gradient flow converts the problem of separating unknown delayed mixtures of sources, from traveling waves impinging on .an array of sensors, into a simpler problem of separating unknown instantaneous mixtures of the time-differentiated sources, obtained by acquiring or computing spatial and temporal derivatives on the array. The linear coefficients in the instantaneous mixture directly represent the delays, which in tum determine the direction angles of the sources. This formulation is attractive, since it allows to separate and localize waves of broadband signals using standard tools of independent component analysis (ICA), yielding the sources along with their direction angles. The technique is suited for arrays of small aperture, with dimensions shorter than the coherence length of the waves. We present gradient flow experiments on an array of four hearing aid microphones placed within a 5 mm radius, yielding 20 dB separation of joint speech in outdoors acoustic environments, and 10 dB separation indoors under mild reverberant conditions. These results suggest applications of gradient flow miniature microphone arrays to intelligent hearing aids with adaptive suppression of interfering signals and nonstationary noise.

16-channel wide-range VLSI potentiostat array

A 16-channel current-measuring VLSI sensor array system for electrochemical detection of electroactive neurotransmitters like dopamine and nitric-oxide is presented. The designed ADC architecture is first-order single bit delta-sigma modulator with programmable oversampling ratio. The modulation of feedback duty-cycle in modulator design enables choice of current range in accordance to magnitude and time constant of signal leading to current range that spans over six orders of magnitude and sensitivity up to picoamperes at hundred millisecond conversion time with power consumption of 300 /spl mu/W. A 3 mm /spl times/ 3 mm chip in 0.5 /spl mu/m CMOS technology is used for real-time multi-channel acquisition of neurotransmitter concentration.