Farhat, Nabil H
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Publication Corticonic models of brain mechanisms underlying cognition and intelligence(2007-08-14) Farhat, Nabil HThe concern of this review is brain theory or more specifically, in its first part, a model of the cerebral cortex and the way it:(a) interacts with subcortical regions like the thalamus and the hippocampus to provide higher-level-brain functions that underlie cognition and intelligence, (b) handles and represents dynamical sensory patterns imposed by a constantly changing environment, (c) copes with the enormous number of such patterns encountered in a lifetime bymeans of dynamic memory that offers an immense number of stimulus-specific attractors for input patterns (stimuli) to select from, (d) selects an attractor through a process of “conjugation” of the input pattern with the dynamics of the thalamo–cortical loop, (e) distinguishes between redundant (structured)and non-redundant (random) inputs that are void of information, (f) can do categorical perception when there is access to vast associative memory laid out in the association cortex with the help of the hippocampus, and (g) makes use of “computation” at the edge of chaos and information driven annealing to achieve all this. Other features and implications of the concepts presented for the design of computational algorithms and machines with brain-like intelligence are also discussed. The material and results presented suggest, that a Parametrically Coupled Logistic Map network (PCLMN) is a minimal model of the thalamo–cortical complex and that marrying such a network to a suitable associative memory with re-entry or feedback forms a useful, albeit, abstract model of a cortical module of the brain that could facilitate building a simple artificial brain. In the second part of the review, the results of numerical simulations and drawn conclusions in the first part are linked to the most directly relevant works and views of other workers. What emerges is a picture of brain dynamics on the mesoscopic and macroscopic scales that gives a glimpse of the nature of the long sought after brain code underlying intelligence and other higher level brain functions. Physics of Life Reviews 4 (2007) 223–252 © 2007 Elsevier B.V. All rights reserved.Publication GBOPCAD: A Synthesis Tool for High-Performance Gain-Boosted Opamp Design(2005-08-01) Yuan, Jie; Farhat, Nabil H; Van der Spiegel, JanA systematic design methodology for high-performance gain-boosted opamps (GBOs) is presented. The methodology allows the optimization of the GBO in terms of ac response and settling performance and is incorporated into an automatic computer-aided design (CAD) tool, called GBOPCAD. Analytic equations and heuristics are first used by GBOPCAD to obtain a sizing solution close to the global optimum. Then, simulated annealings are used by GBOPCAD to find the global optimum. A sample opamp is designed by this tool in a 0.6-μm CMOS process. It achieves a dc gain of 80 dB, a unity-gain bandwidth of 836 MHz with 60o phase margin and a 0.0244% settling time of 5 ns. The sample/hold front-end of a 12-bit 50-MSample/s analog–digital converter was implemented with this opamp. It achieves a signal-to-noise ratio of 81.9 dB for a 8.1-MHz input signal.Publication Cort-X II: Low Power Element Design of a Large-Scale Spatio-Temporaral Pattern Clustering System(2007-05-01) Yuan, Jie; Farhat, Nabil H; Song, Ning; Van der Spiegel, JanComplex spatio-temporal patterns can be clustered using a network of parametrically coupled logistic maps. This paper describes the processing element design of such a Cort-X system. Each Cort-X element consists of a non-linear coupling (LC) and a non-linear dynamic element (IRON). The circuits are designed for low-power operation and to be robust against process variations. This has been accomplished by using openloop circuits, and a self-calibration technique that compensate for process variations. The circuits were implemented in a 0.25 um, 2.5V CMOS process and consumes a total of 12mW of power at 1MHz which is about a factor of 20 less power than previous realizations. This opens the possibility for building a large-scale Cort-X system on a chip for the recognition of complex spatio-temporal patterns.Publication Optical Realization of the Retinal Ganglion Receptive Fields in Electron-Trapping Material Thin Film(2006-04-01) Pashaie, Ramin; Farhat, Nabil HOptical control of the electron-trapping material is used to model the retinal ganglion cell’s receptive field. Using this approach all the retinal image processing can be done on the surface of a thin film of this material.Publication Optical Realization of Bio-inspired Spiking Neurons In Electron Trapping Material Thin(2007-10-27) Pashaie, Ramin; Farhat, Nabil H.A thin film of electron-trapping material (ETM), when combined with suitable optical bistability, is considered as medium for optical implementation of bio-inspired neural nets. The optical mechanism of ETM under blue light and NIR exposure has the inherent ability at the material level to mimic the crucial components of the stylized Hodgkin-Huxley model of biological neuron. Combining this unique property with high resolution capability of ETM, a dense network of bio-inspired neurons can be realized in a thin film of this infrared stimulable storage phosphore. The work presented here, when combined with suitable optical bistability and optical interconnectivity, has the potential of producing an artificial nonlinear excitable medium analogue to cortical tissue.Publication A CMOS Monolithic Implementation of a Nonlinear Element for Arbitrary 1-D Map Generation(2006-05-01) Farhat, Nabil H; Yuan, Jie; Van der Spiegel, JanIn a macroscopic approach, a single-chip cortical patch is designed based on a the model of a bifurcating neuron. In this paper, the monolithic design of the bifurcating neuron is presented. The dynamic element is able to generate an arbitrary one-dimensional map with 12-bit resolution. The CMOS design employs a calibration scheme to maintain robustness against process variations. The element is fabrication in a 0.6um CMOS process, and it driven under signals with 1MHz frequency. It covers a die of 0.2 square mm, and consumes 40mW power, with a 5V supply.Publication Dynamics of electron-trapping materials under blue light and near infrared exposure: an improved model(2007-08-13) Pashaie, Ramin; Farhat, Nabil HDynamics of electron-trapping materials (ETMs) is investigated. Based on experimental observations, evolution of the ETM's luminescence is mathematically modeled by a nonlinear differential equation. This improved model can predict dynamics of ETM under blue light and near-infrared (NIR) exposures during charging, discharging, simultaneous illumination, and in the equilibrium state. The equilibrium-state luminescence of ETM is used to realize a highly nonlinear optical device with potential applications in nonlinear optical signal processing.Publication A CMOS Monolithic Implementation of a Nonliniear Interconnection Module for a Corticonic Network(2006-05-01) Farhat, Nabil H; Yuan, Jie; Van der Spiegel, JanA nonlinear interconnection module for a corticonic network is designed and fabricated in a 0.6µm CMOS process. The module uses NMOS transistors in weak-inversion for nonlinearity. A calibration scheme is developed to compensate for the process and temperature variations of the circuit. The designed module has an area of 0.35 sq. mm2. It consumes 200mW of power, with 5V power supply. Simulation results show that the circuit is able to implement the target parametric coupling function accurately.Publication An analytic model for the dynamics of electron trapping materials with applications in nonlinear optical signal processing(2008-01-01) Pashaie, Ramin; Farhat, Nabil HIn this paper the optical mechanism and dynamics of electron trapping material under simultaneous illumination with two wavelengths is investigated. Our analytical model proves that the equilibrium state luminescence of such a material can be controlled to produce highly nonlinear behavior with potential applications in nonlinear optical signal processing and optical realization of nonlinear dynamical systems. Combining this new approach with state-of-the-art fast spatial light modulators and CCD cameras that can precisely control and measure exposure, large arrays of nonlinear processing elements can be accommodated in a thin film of this material.Publication Realization of Receptive Fields with Excitatory and Inhibitory Responses on Equilibrium-State Luminescence of Electron Trapping Material Thin Film(2007-06-01) Pashaie, Ramin; Farhat, Nabil HOur theoretical modelings and experimental observations illustrate that the equilibrium-state luminescence of electron-trapping materials (ETMs) can be controlled to produce either excitatory or inhibitory responses to the same optical stimulus. Because of this property, ETMs have a unique potential in optical realization of neurobiologically based parallel computations. As a classic example, we have controlled the equilibrium-state luminescence of a thin film of this stimulable storage phosphor to make it behave similarly to the receptive fields of sensory neurons in the mammalian visual system, which are responsible for early visual processing.