The exponential behaviour of MOSFETs in subthreshold operation has recently been exploited to build CMOS translinear circuits such as multipliers and log-domain filters. A major obstacle in developing a practical CMOS...
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The exponential behaviour of MOSFETs in subthreshold operation has recently been exploited to build CMOS translinear circuits such as multipliers and log-domain filters. A major obstacle in developing a practical CMOS implementation is the variation in threshold voltage between devices. In translinear circuits, these voltage offsets manifest themselves as gain errors in the current-mode outputs. We have designed a floating-gate CMOS current mirror that can adapt its gain to compensate for these errors. The adaptation process uses only hot-electron injection, so the high voltages typically associated with tunneling are not needed. A small array of these circuits were fabricated in a standard 1.2 /spl mu/m double-poly CMOS process. We demonstrate gain adaptation and discuss the nonlinearity introduced by the adaptive mirror.
Using the analog VLSI-based saccadic eye movement system previously developed we investigate the use of biologically realistic error signals to calibrate the system in a manner similar to the primate oculomotor system...
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Using the analog VLSI-based saccadic eye movement system previously developed we investigate the use of biologically realistic error signals to calibrate the system in a manner similar to the primate oculomotor system. In this paper we introduce two new circuit components which are used to perform this task, a resettable-integrator model of the burst generator with a floating-gate structure to provide on-chip storage of analog parameters and a directionally-selective motion detector for detecting post-saccadic drift.
The standard theory of a leaky integrator with stochastic spike input predicts that cortical cells should fire regularly. We tested interspike-interval histograms from awake, behaving macaque visual cortex (V1 and MT)...
The standard theory of a leaky integrator with stochastic spike input predicts that cortical cells should fire regularly. We tested interspike-interval histograms from awake, behaving macaque visual cortex (V1 and MT), and found high levels of variability (CV>0.5) characteristic of a nearly random (Poisson) process. A simple integrate-and-fire model, using accepted biophysical parameters, fails by more than a factor of ten to account for the high CV. We also simulated a biophysically detailed compartment-model of an anatomically reconstructed and physiologically characterized layer V pyramidal cell; again, at high firing rate, CV values are low, in disagreement with the data. Only a few situations could account for this discrepency: very large EPSP’s, a very short membrane time constant (τm<0.3 msec), highly synchronized input, or spikes in excitable dendrites. Our analysis suggests that cortical computation may occur at a time-scale much faster than previously realized.
Based on anatomical and physiological data, we have developed a computer simulation of piri-form (olfactory) cortex which is capable of reproducing spatial and temporal patterns of actual cortical activity under a var...
Based on anatomical and physiological data, we have developed a computer simulation of piri-form (olfactory) cortex which is capable of reproducing spatial and temporal patterns of actual cortical activity under a variety of conditions. Using a simple Hebb-type learning rule in conjunction with the cortical dynamics which emerge from the anatomical and physiological organization of the model, the simulations are capable of establishing cortical representations for different input patterns. The basis of these representations lies in the interaction of sparsely distributed, highly divergent/convergent interconnections between modeled neurons. We have shown that different representations can be stored with minimal interference. and that following learning these representations are resistant to input degradation, allowing reconstruction of a representation following only a partial presentation of an original training stimulus. Further, we have demonstrated that the degree of overlap of cortical representations for different stimuli can also be modulated. For instance similar input patterns can be induced to generate distinct cortical representations (discrimination). while dissimilar inputs can be induced to generate overlapping representations (accommodation). Both features are presumably important in classifying olfactory stimuli.
We present three different architectures that make use of analog VLSI velocity sensors for detecting the focus of expansion, time to contact and motion discontinuities respectively. For each of the architectures propo...
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We present three different architectures that make use of analog VLSI velocity sensors for detecting the focus of expansion, time to contact and motion discontinuities respectively. For each of the architectures proposed we describe the functionality of their component modules and their principles of operation. Data measurements obtained from the VLSI chips developed demonstrate their correct performance and their limits of operation.
Feature detection and tracking is a fundamental problem in computer vision research. By detecting and tracking features in an image sequence it is possible to recover information on both the motion of the viewer and t...
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