Albert H. Titus

An analog VLSI chip emulating polarization vision of octopus retina

Biological systems provide a wealth of information which form the basis for human-made artificial systems. In this work, the visual system of Octopus is investigated and its polarization sensitivity mimicked. While in actual Octopus retina, polarization vision is mainly based on the orthogonal arrangement of its photoreceptors, our implementation uses a birefringent micropolarizer made of YVO/sub 4/ and mounted on a CMOS chip with neuromorphic circuitry to process linearly polarized light. Arranged in an 8/spl times/5 array with two photodiodes per pixel, each consuming typically 10 /spl mu/W, this circuitry mimics both the functionality of individual Octopus retina cells by computing the state of polarization and the interconnection of these cells through a bias-controllable resistive network.

CMOS-Based Phase Fluorometric Oxygen Sensor System

The design and development of a phase fluorometric oxygen (O2 ) sensor system using single-chip CMOS detection and processing integrated circuit (DPIC) and sol-gel derived xerogel thin-film sensor elements is described. The sensor system determines analyte concentrations using the excited state lifetime measurements of an O2-sensitive luminophore (tris(4,7-diphenyl-1,10- phenathroline)ruthenium (II)) embedded in the xerogel matrix. A light emitting diode (LED) is used as the excitation source, and the fluorescence is detected by the DPIC using a 16times16 phototransistor array on-chip. The DPIC also consists of a current mirror, current-to-voltage converter, amplifier, bandpass filter, and phase detector. The DPIC output is a dc voltage that corresponds to the detected fluorescence phase shift. With a 14-kHz modulation frequency, the entire system including driving the LED consumes 80 mW of average power. The sensor system provides stable, reproducible, analytically reliable, and fast response (~20 s) to changes in the gaseous oxygen concentrations and establishes the viability for low cost, low power and miniaturized biochemical sensor systems

Colorimetric porous photonic bandgap sensors with integrated CMOS color detectors

In this paper, the development of a novel colorimetric sensor system based on the integration of complementary metal-oxide-semiconductor (CMOS) color detectors with a modified porous polymeric photonic bandgap sensor is reported. The color detector integrated circuit IC is implemented with AMI (AMI Semiconductor) 1.5 mum technology, a standard CMOS fabrication process available at MOSIS (http://www.mosis.org). The color detectors are based on the spectral responses of buried double junctions (BDjs) and stacked triple junctions (STJs); the ratio of the photocurrents at the junctions provides spectral information. Both types of color detectors are characterized with a monochromator, and the results are compared. The BDJ color detector is used with a porous photonic bandgap reflection grating whose reflection spectra shifts as a function of the concentration of vapor analyte present. The experimental results verify that the color change of the photonic crystal can be detected and correlated to the change in analyte concentration. The entire system is compact and low power

Chemical sensing systems using xerogel-based sensor elements and CMOS photodetectors

We present the first example of an integrated complementary metal-oxide-semiconductor (CMOS) photodetector coupled with a solid-state xerogel-based thin-film sensor to produce a compact chemical sensor system. We compare results using two different CMOS-based detector systems to results obtained by using a standard photomultiplier tube (PMT) or charge-coupled device (CCD) detector. Because the chemical sensor elements are governed by a Stern-Volmer relationship, the Stern-Volmer quenching constant is used as the primary comparator between the different detectors. All of the systems yielded Stern-Volmer constants from 0.042 to 0.049 O/sub 2/%/sup -1/. The results show that the CMOS detector system yields analytical data that are comparable to the CCD- and PMT-based systems. The disparity between the data obtained from each detector is primarily associated with the difference in how the signals are obtained by each detector as they presently exist. We have also observed satisfactory reversibility in the operation of the sensor system. The CMOS-based system exhibits a response time that is faster than the chemical sensor elements intrinsic response time, making the CMOS suitable for time-dependent measurements. The CMOS array detector also uses less than 0.1% the power in comparison to a standard PMT or CCD. The combined xerogel/CMOS system represents an important step toward the development of a portable, efficient sensor system.

A new wide range Euclidean distance circuit for neural network hardware implementations

In this paper, we describe an analog very large-scale integration (VLSI) implementation of a wide range Euclidean distance computation circuit - the key element of many synapse circuits. This circuit is essentially a wide-range absolute value circuit that is designed to be as small as possible (80 /spl times/ 76 /spl mu/m) in order to achieve maximum synapse density while maintaining a wide range of operation (0.5 to 4.5 V) and low power consumption (less than 200 /spl mu/W). The circuit has been fabricated in 1.5-/spl mu/m technology through MOSIS. We present simulated and experimental results of the circuit, and compare these results. Ultimately, this circuit is intended for use as part of a high-density hardware implementation of a self-organizing map (SOM). We describe how this circuit can be used as part of the SOM and how the SOM is going to be used as part of a larger bio-inspired vision system based on the octopus visual system.

Multilevel category structure in the ART-2 network

Multilevel categorization is investigated within the context of analog activity patterns on the output layer of an ART 2 network. The ART 2 network parameters are analyzed in terms of stable category formation and in terms of the number of nodes in the output layer that can become most active. The resulting activity patterns on the output layer demonstrate a multilevel category structure based on the relative differences between patterns that exist for many different values of the vigilance parameter. We have shown that the information contained in the output analog patterns can be interpreted in several different ways, which is not possible when the category is represented by a single winning node. Also, favorable comparisons are also demonstrated between the category structure emerging from the set of category patterns and principles of categorization in psychology and neurobiology.

O 2 -Responsive Chemical Sensors Based on Hybrid Xerogels that Contain Fluorinated Precursors

We report the development and analytical figures of merit associated with several new O2-responsive sensor materials. These new sensing materials are formed by sequestering the luminophore tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ([Ru(dpp)3]2+) within hybrid xerogels that are composed of two of the following methoxysilanes: tetramethoxysilane, n-propyl-trimethoxysilane, 3,3,3-trifluoropropyl-trimethoxysilane, phenethyl-trimethoxysilane, and pentafluorophenylpropyl-trimethoxysilane. Steady-state and time-resolved luminescence measurements are used to investigate these hybrid xerogel-based sensor materials and elucidate the underlying reasons for the observed performance. The results show that many of the [Ru(dpp)3]2+-doped composites form visually uniform, crack-free xerogel films that can be used to construct O2 sensors that have linear calibration curves and excellent long-term stability. To the best of our knowledge, the [Ru(dpp)3]2+-doped fluorinated hybrid xerogels also exhibit the highest O2 sensitivity of any reported [Ru(dpp)3]2+-based sensor platform.

CMOS Neuromorphic Optical Sensor Chip With Color Change-Intensity Change Disambiguation (CCICD)

In this paper, we propose a novel terrestrial retina-like neuromorphic sensor chip which can (1) perform irradiance and color detection via two pathways simultaneously and (2) can perform color change-intensity change disambiguation (CCICD). The irradiance detection pathway has a wide-dynamic detection range, spanning 3 orders of magnitude, and is robust to background light variations. The color detection pathway has a buried double junction photodiode as the photoreceptor followed by two parallel logarithmic I-V convertors whose outputs go to a differential amplifier. The output from this pathway is a color response which has roughly 50 nm resolution for wavelengths from 400 to 700 nm, and 22 nm resolution between 700-900 nm. With these two pathways, we can perform CCICD to determine if a change in the output of the irradiance pathway is because of irradiance change, color change, or both. This terrestrial retina-like neuromorphic sensor chip is implemented in AMI 1.5 mum technology, a standard CMOS fabrication process available at MOSIS.

An Analog VLSI Velocity Sensor System for Depth Perception

The authors present a neuromorphic analog very large scale integration integrated circuit (IC)-based system for determining the relative depth of objects in a scene. This system called the depth through motion parallax (DTMP) system computes the depth of an object in its field of view using the DTMP algorithm-an algorithm that is based on psychophysical studies of vision in humans. The IC computes the apparent velocity of the object from the measured transit times (the time it takes for the image to move from one pixel to the next) and consumes an average power of less than 2 mW. To compute the depth of a stationary or moving object, the authors accelerate the observer using a motion controller and obtain the apparent acceleration (change in the apparent velocity) rather than just the apparent velocity. The experimental results demonstrate that the sensor can be used to provide accurate relative depth information of the objects based on their apparent accelerations. The description of a fully self-contained system based on the prototype DTMP system is also presented

CMOS mixed-signal phase detector for integrated chemical sensor systems

The development of a portable chemical sensor system based on the measurement of the excited-state lifetimes of luminophore doped xerogels in the frequency-domain is described. The prototype sensor system is demonstrated for oxygen (O2) monitoring and consists of a silicon photodiode as the detector followed by a current-to-voltage converter, an amplifier, a band-pass filter and a custom-designed CMOS phase detector. The variation in the lifetime, due a change in the analyte concentration, is measured as a phase shift between a sinusoidally modulated reference excitation and the fluorescence emission using the designed CMOS phase shift detector. The CMOS mixed-signal phase detector is fabricated using the AMI 1.5 mum process available through MOSIS. A highly accurate, low cost, and hand-held prototype oxygen sensor is demonstrated using this CMOS phase detector