15,754 research outputs found
Current-Mode Techniques for the Implementation of Continuous- and Discrete-Time Cellular Neural Networks
This paper presents a unified, comprehensive approach
to the design of continuous-time (CT) and discrete-time
(DT) cellular neural networks (CNN) using CMOS current-mode
analog techniques. The net input signals are currents instead
of voltages as presented in previous approaches, thus avoiding
the need for current-to-voltage dedicated interfaces in image
processing tasks with photosensor devices. Outputs may be either
currents or voltages. Cell design relies on exploitation of current
mirror properties for the efficient implementation of both linear
and nonlinear analog operators. These cells are simpler and
easier to design than those found in previously reported CT
and DT-CNN devices. Basic design issues are covered, together
with discussions on the influence of nonidealities and advanced
circuit design issues as well as design for manufacturability
considerations associated with statistical analysis. Three prototypes
have been designed for l.6-pm n-well CMOS technologies.
One is discrete-time and can be reconfigured via local logic for
noise removal, feature extraction (borders and edges), shadow
detection, hole filling, and connected component detection (CCD)
on a rectangular grid with unity neighborhood radius. The other
two prototypes are continuous-time and fixed template: one for
CCD and other for noise removal. Experimental results are given
illustrating performance of these prototypes
Density-matrix theory of the optical dynamics and transport in quantum cascade structures: The role of coherence
The impact of coherence on the nonlinear optical response and stationary
transport is studied in quantum cascade laser structures. Nonequilibrium
effects such as pump-probe signals, the spatio-temporally resolved electron
density evolution, and the subband population dynamics (Rabi flopping) as well
as the stationary current characteristics are investigated within a microscopic
density-matrix approach. Focusing on the stationary current and the recently
observed gain oscillations, it is found that the inclusion of coherence leads
to observable coherent effects in opposite parameter regimes regarding the
relation between the level broadening and the tunnel coupling across the main
injection barrier. This shows that coherence plays a complementary role in
stationary transport and nonlinear optical dynamics in the sense that it leads
to measurable effects in opposite regimes. For this reason, a fully coherent
consideration of such nonequilibrium structures is necessary to describe the
combined optical and transport propertiesComment: 14 pages, 11 figures; final versio
Bifurcation analysis of a semiconductor laser with filtered optical feedback
We study the dynamics and bifurcations of a semiconductor laser with delayed filtered optical feedback, where a part of the output of the laser reenters after spectral filtering. This type of coherent optical feedback is more challenging than the case of conventional optical feedback from a simple mirror, but it provides additional control over the output of the semiconductor laser by means of choosing the filter detuning and the filter width. This laser system can be modeled by a system of delay differential equations with a single fixed delay, which is due to the travel time of the light outside the laser. In this paper we present a bifurcation analysis of the filtered feedback laser. We first consider the basic continuous wave states, known as the external filtered modes (EFMs), and determine their stability regions in the parameter plane of feedback strength versus feedback phase. The EFMs are born in saddle-node bifurcations and become unstable in Hopf bifurcations. We show that for small filter detuning there is a single region of stable EFMs, which splits up into two separate regions when the filter is detuned. We then concentrate on the periodic orbits that emanate from Hopf bifurcations. Depending on the feedback strength and the feedback phase, two types of oscillations can be found. First, there are undamped relaxation oscillations, which are typical for semiconductor laser systems. Second, there are oscillations with a period related to the delay time, which have the remarkable property that the laser frequency oscillates while the laser intensity is almost constant. These frequency oscillations are only possible due to the interaction of the laser with the filter. We determine the stability regions in the parameter plane of feedback strength versus feedback phase of the different types of oscillations. In particular, we find that stable frequency oscillations are dominant for nonzero values of the filter detuning. © 2007 Society for Industrial and Applied Mathematics
Generation of slow intense optical solitons in a resonance photonic crystal
We demonstrate interesting and previously unforeseen properties of a pair of
gap solitons in a resonant photonic crystal which are predicted and explained
in a physically transparent form using both analytical and numerical methods.
The most important result is the fact that an oscillating gap soliton created
by the presence of a localized population inversion inside the crystal can be
manipulated by means of a proper choice of bit rate, phase and amplitude
modulation. Developing this idea, we are able to obtain qualitatively different
regimes of a resonant photonic crystal operation. In particular, a noteworthy
observation is that both the delay time and amplitude difference must exceed a
certain level to ensure effective control over the soliton dynamics
A 10-bit Charge-Redistribution ADC Consuming 1.9 μW at 1 MS/s
This paper presents a 10 bit successive approximation ADC in 65 nm CMOS that benefits from technology scaling. It meets extremely low power requirements by using a charge-redistribution DAC that uses step-wise charging, a dynamic two-stage comparator and a delay-line-based controller. The ADC requires no external reference current and uses only one external supply voltage of 1.0 V to 1.3 V. Its supply current is proportional to the sample rate (only dynamic power consumption). The ADC uses a chip area of approximately 115--225 μm2. At a sample rate of 1 MS/s and a supply voltage of 1.0 V, the 10 bit ADC consumes 1.9 μW and achieves an energy efficiency of 4.4 fJ/conversion-step
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