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     

Power harvesting and telemetry in CMOS for implanted devices

Implanted sensors offer many advantages to study and monitor the human body. Wires or batteries often compromise their usefulness. We describe a telemetry chip that by inductive coupling supplies power to and transmits digital data from an implantable sensor. The same two coils are used to transmit both power and data. The chip fabricated in 0.5-/spl mu/m CMOS technology supplies 1.7 mA at 3.3 V, over a distance up to 25 mm between coils. Experiments emulating the effect of human tissue by introducing water bearing colloids between the two coils revealed a negligible loss of transfer efficiency. With modified Miller encoding, the data link attained 3 10/sup -5/ bit error rate at 10 kbps transmission speed over 25 mm distance. Repeated tests using the same colloids between coils resulted in a slight decrease in the signal to noise ratio of the data stream with increasing thickness.     

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.     

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