Papers by Andreas Andreou
Neural Networks, 2001
We present a scheme for implementing highly-connected, recon®gurable networks of integrate-and-®r... more We present a scheme for implementing highly-connected, recon®gurable networks of integrate-and-®re neurons in VLSI. Neural activity is encoded by spikes, where the address of an active neuron is communicated through an asynchronous request and acknowledgement cycle. We employ probabilistic transmission of spikes to implement continuous-valued synaptic weights, and memory-based look-up tables to implement arbitrary interconnection topologies. The scheme is modular and scalable, and lends itself to the implementation of multi-chip network architectures. Results from a prototype system with 1024 analog VLSI integrate-and-®re neurons, each with up to 128 probabilistic synapses, demonstrate these concepts in an image processing task. q
IEEE Transactions on Robotics and Automation, 1997
Page 1. IEEE TRANSACTIONS ON ROBOTICS AND AUTOMATION, VOL. 13, NO. 2, APRIL 1997 195 Liquid Cryst... more Page 1. IEEE TRANSACTIONS ON ROBOTICS AND AUTOMATION, VOL. 13, NO. 2, APRIL 1997 195 Liquid Crystal Polarization Camera Lawrence B. Wolff, Todd A. Mancini, Philippe Pouliquen, and Andreas G. Andreou Abstract ...
IEEE Transactions on Circuits and Systems Ii: Analog and Digital Signal Processing, 1998
We present an analog VLSI chip intended to serve as a front end of a speech recognition system. T... more We present an analog VLSI chip intended to serve as a front end of a speech recognition system. The chip architecture is inspired by biological auditory models common to humans and primate vertebrates. We include experimental results on a 1.2-μm CMOS custom analog VLSI implementation and speech recognition results obtained from software simulations of the hardware on the TI-DIGITS database
Proceedings of The IEEE, 2001
We outline a theoretical framework to analyze information processing in biological sensory organs... more We outline a theoretical framework to analyze information processing in biological sensory organs and in engineered microsystems. We employ the mathematical tools of communication theory and model natural or synthetic physical structures as microscale communication networks, studying them under physical constraints at two different levels of abstraction. At the functional level, we examine the operational and task specification, while at the physical level, we examine the material specification and realization. Both levels of abstraction are characterized by Shannon's channel capacity, as determined by the channel bandwidth, the signal power, and the noise power. The link between the functional level and the physical level of abstraction is established through models for transformations on the signal, physical constraints on the system, and noise that degrades the signal.
Speech Communication, 1998
We present the theory for heteroscedastic discriminant analysis (HDA), a model-based generalizati... more We present the theory for heteroscedastic discriminant analysis (HDA), a model-based generalization of linear discriminant analysis (LDA) derived in the maximum-likelihood framework to handle heteroscedastic-unequal variance-classi®er models. We show how to estimate the heteroscedastic Gaussian model parameters jointly with the dimensionality reducing transform, using the EM algorithm. In doing so, we alleviate the need for an a priori ad hoc class assignment. We apply the theoretical results to the problem of speech recognition and observe word-error reduction in systems that employed both diagonal and full covariance heteroscedastic Gaussian models tested on the TI-DIGITS database. Ó
This paper revises the conditions under which the translinear principle can be fully exploited fo... more This paper revises the conditions under which the translinear principle can be fully exploited for MOS transistors operating in subthreshold. Due to the exponential nature of subthreshold MOS transistors, the translinear principle applies immediately as long as the source-to-bulk voltages are made equal to zero (or constant). This paper addresses the conditions under which subthreshold MOS transistors still satisfy a translinear principle, but without imposing this constraint on all VBS voltages. It is found that the translinear principle results in a more general formulation than the originally found for BJT's since now multiple translinear loops can be involved. The constraint of an even number of transistors is no longer necessary. Some corollaries are stated as well and, finally, it is shown how to use the theorem for subthreshold MOS transistors operated in the ohmic regime.
Abstract We present the design and testing of a micropower integrated circuit for the estimation ... more Abstract We present the design and testing of a micropower integrated circuit for the estimation of the bearing angle of a sound source with respect to a pair of microphones. The algorithm is based on a modified binary cross-correlation approach suitable for low-power operation. The circuit has been tested and operates at 600 μW at performance levels matching theoretical simulations.
IEEE Transactions on Circuits and Systems I-regular Papers, 2004
Sound localization using energy-aware hardware for sensor networks nodes is a problem with many a... more Sound localization using energy-aware hardware for sensor networks nodes is a problem with many applications in surveillance and security. In this paper, we evaluate four algorithms for sound localization using signals recorded in a natural environment with an array of commercial off-the-shelf microelectromechanical systems microphones and a specially designed compact acoustic enclosure. We evaluate performance of the algorithms and their hardware complexity which relates directly to energy consumption.
Neural Computation, 1989
We present a new approach to the engineering of collective analog computing systems that emphasiz... more We present a new approach to the engineering of collective analog computing systems that emphasizes the role of currents as an appropriate signal representation and the need for low-power dissipation and simplicity in the basic functional circuits. The design methodology and implementation style that we describe are inspired by the functional and organizational principles of neuronal circuits in living systems. We have implemented synthetic neurons and synapses in analog CMOS VLSI that are suitable for building associative memories and self-organizing feature maps.
Journal of The Acoustical Society of America, 1995
The performance of speech recognition systems is often improved by accounting explicitly for sour... more The performance of speech recognition systems is often improved by accounting explicitly for sources of variability in the data. In the SWITCHBOARD corpus, studied during the 1994 CAIP workshop [Frontiers in Speech Processing Workshop II, CAIP (August 1994)], an attempt ...
The engineering of analog VLSI processors for computer vision is discussed. These are based on th... more The engineering of analog VLSI processors for computer vision is discussed. These are based on the Hassenstein-Reichardt-Poggio models for information processing in the visual systems of the fly. It is shown how neural network models can be mapped on silicon integrated circuits for performing tasks that can be handled efficiently by digital computing machinery. Hardware architectures for both position and motion computation are described
We describe a novel scheme for asynchronous communication of information out of two dimensional p... more We describe a novel scheme for asynchronous communication of information out of two dimensional processing arrays. Our architecture employs analog Winner Takes All (WTA) circuits instead of digital binary-tree arbiters found in other designs. A small system that incorporates an array of 9×12 pixels has been fabricated in a 2μ, double polysilicon, double metal process. Experimental results verify system functionality
Image and Vision Computing, 1995
Recently, polarization vision has been shown to simplify some important image understanding tasks... more Recently, polarization vision has been shown to simplify some important image understanding tasks that can be more diff'cult to perform with intensity vision alone. This, together with the more general capabilities of polarization vision for image understanding, motivates the building of camera sensors that automatically sense and process polarization information. Described in this paper are a variety of designs for polarization camera sensors that have been built to automatically sense partial linearly polarized light, and computationally process this sensed polarization information at pixel resolution to produce a visualization of reflected polarization from a scene, and/or a visualization of physical information in a scene directly related to sensed polarization. The three designs for polarization camera sensors presented utilize (i) serial acquisition of polarization components using liquid crystals, (ii) parallel acquisition of polarization components using a stereo pair of cameras and a polarizing beamsplitter, and (iii) a prototype photosensing chip with three scanlines, each scanline coated with a particular orientation of polarizing material. As the sensory input to polarization camera sensors subsumes that of standard intensity cameras, they can potentially significantly expand the application potential of computer vision. A number of images taken with polarization cameras are presented, showing potential applications to image understanding, object recognition, circuit board inspection and marine biology.
IEEE Transactions on Neural Networks, 1992
An analog CMOS integration of a model for the auditory periphery is presented. The model consists... more An analog CMOS integration of a model for the auditory periphery is presented. The model consists of middle ear, basilar membrane, and hair cell/synapse modules which are derived from neurophysiological studies. The circuit realization of each module is discussed, and experimental data of each module's response to sinusoidal excitation are given. The nonlinear speech processing capabilities of the system are demonstrated using the voiced syllable |ba|. The multichannel output of the silicon model corresponds to the time-varying instantaneous firing rates of auditory nerve fibers that have different characteristic frequencies. These outputs are similar to the physiologically obtained responses. The actual implementation uses subthreshold CMOS technology and analog continuous-time circuits, resulting in a real-time, micropower device with potential applications as a preprocessor of auditory stimuli.
IEEE Sensors Journal, 2002
Page 1. 566 IEEE SENSORS JOURNAL, VOL. 2, NO. 6, DECEMBER 2002 Polarization Imaging: Principles a... more Page 1. 566 IEEE SENSORS JOURNAL, VOL. 2, NO. 6, DECEMBER 2002 Polarization Imaging: Principles and Integrated Polarimeters Andreas G. Andreou and Zaven Kevork Kalayjian AbstractPolarization is a general descriptor ...
Page 1. 1398 IEEE TRANSACTIONS ONCIRCUITS AND SYSTEMSI: FUNDAMENTAL THEORY AND APPLICATIONS, VOL... more Page 1. 1398 IEEE TRANSACTIONS ONCIRCUITS AND SYSTEMSI: FUNDAMENTAL THEORY AND APPLICATIONS, VOL. 46, NO. 11, NOVEMBER 1999 to apply these results for developing new robust nonlinear control laws based on dynamic neural networks. ...
Analog Integrated Circuits and Signal Processing, 1996
In this paper we provide an overview of translinear circuit design using MOS transistors operatin... more In this paper we provide an overview of translinear circuit design using MOS transistors operating in subthreshold region. We contrast the bipolar and MOS subthreshold characteristics and extend the translinear principle to the subthreshold MOS ohmic region through a drain/source current decomposition. A front/back-gate current decomposition is adopted; this facilitates the analysis of translinear loops, including multiple input floating gate MOS transistors. Circuit examples drawn from working systems designed and fabricated in standard digital CMOS oriented process are used as vehicles to illustrate key design considerations, systematic analysis procedures, and limitations imposed by the structure and physics of MOS transistors. Finally, we present the design of an analog VLSI “translinear system” with over 590,000 transistors in subthreshold CMOS. This performs phototransduction, amplification, edge enhancement and local gain control at the pixel level.
Page 1. Multiple Input Floating-Gate MOS Differential Amplifiers and Applications for Analog Comp... more Page 1. Multiple Input Floating-Gate MOS Differential Amplifiers and Applications for Analog Computation Kewei Yang and Andreas G. Andreou Department of Electrical and Computer Engineering The Johns Hopkins University Baltimore, Maryland 21218 USA ...
IEEE Transactions on Neural Networks, 1991
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Papers by Andreas Andreou