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Ravelo B.,CNRS Research Institute for Embedded Electronic Systems
Electronics Letters | Year: 2011

This presented report deals with the synthesis of baseband negative group delay (NGD) RF circuits. A theoretical approach based on the S-parameter analysis is presented. The NGD circuit synthesis formulae according to the desired gain value, NGD level and bandwidth are established. To validate the theoretical approach, a two-stage NGD device employing LNAs was investigated. Baseband NGD with minimal value below -1ns with 400MHz frequency bandwidth was found. The synthesised circuit presents a gain higher than 5dB. To highlight the functionality of the NGD effect, time-domain analysis was performed. The NGD circuit allows the reduction of signal pure delays caused by telecom devices and is useful for the correction of interleaved symbols in RF/digital numerical systems. © 2011 The Institution of Engineering and Technology. Source


Dupuis Y.,CNRS Research Institute for Embedded Electronic Systems
IEEE transactions on image processing : a publication of the IEEE Signal Processing Society | Year: 2013

Bio-inspired and non-conventional vision systems are highly researched topics. Among them, omnidirectional vision systems have demonstrated their ability to significantly improve the geometrical interpretation of scenes. However, few researchers have investigated how to perform object detection with such systems. The existing approaches require a geometrical transformation prior to the interpretation of the picture. In this paper, we investigate what must be taken into account and how to process omnidirectional images provided by the sensor. We focus our research on face detection and highlight the fact that particular attention should be paid to the descriptors in order to successfully perform face detection on omnidirectional images. We demonstrate that this choice is critical to obtaining high detection rates. Our results imply that the adaptation of existing object-detection frameworks, designed for perspective images, should be focused on the choice of appropriate image descriptors in the design of the object-detection pipeline. Source


Ravelo B.,CNRS Research Institute for Embedded Electronic Systems
EPJ Applied Physics | Year: 2011

This paper introduces theoretic and experimental analyses of short-duration pulse propagation through a negative group delay (NGD) circuit. The basic analysis method of this electronic circuit operating in baseband and microwave frequencies is investigated. Then, its electrical fundamental characteristics vis-à-vis transient signals are developed. To validate the theoretic concept, planar hybrid devices with one- and two-stage NGD cells were designed, simulated, fabricated and tested. Transient analyses with ultra-wide band (UWB) pulse signals with different widths are realized. Then, experimental results in good agreement with the theoretical predictions were observed. Consequently, group delay going down under -2.5 ns is evidenced in baseband frequency up to 63 MHz with one-stage NGD cell. In time-domain, a Gaussian pulse in advance of about t0 = -1.5 ns or 20% of its half-height time-width was measured. This corresponds to a negative group velocity of about vg = L/t 0 = -0.13c (L is the physical length of the tested device and c is light speed in the vacuum). More significant NGD value over 100-MHz bandwidth is stated with two-stage NGD cells. This results in a Gaussian pulse peak advance of about -5 ns (raising a group velocity of about vg = -0.12c) or 31% of its half-height time-width. Finally, some potential applications based on the NGD function are discussed. © EDP Sciences, 2011. Source


Ravelo B.,CNRS Research Institute for Embedded Electronic Systems
Electromagnetics | Year: 2011

In this article, a fundamental analytical approach and experimental verification of a radio frequency active circuit capable of exhibiting negative group delay at microwave wavelengths are presented. By using the S-parameter theory, basic properties and characteristics of the negative group delay circuit under study are established. To highlight the functionality principle of this innovative circuit, time-domain investigations based on ultra-wide-band pulse signal tests are performed. Then, the mechanism of propagating output signal envelopes in time advance compared to the input is demonstrated. To validate this concept, a prototype of a negative group delay device was designed, fabricated, and tested. Experimental results in good agreement with theory and simulation were obtained. In the frequency domain, a negative group delay of about -2.5 ns with amplification of 2 dB was measured at around 622 MHz. Due to this negative group delay effect, envelope advance of about -1.5 ns was observed by considering a pulse signal with a half-height full-width of 10 ns, which modulates a sine carrier with a frequency of 622 MHz. The negative group delay topology presented is potentially useful for the compensation of radio frequency/microwave signal delays. © 2011 Copyright Taylor and Francis Group, LLC. Source


Raveloa B.,CNRS Research Institute for Embedded Electronic Systems
EPJ Applied Physics | Year: 2012

A relevant modeling-method of distributed interconnect line for the high-speed signal integrity (SI) application is introduced in this paper. By using the microwave and transmission line (TL) theory, the interconnect lines are assumed as its distributed RLC-model. Then, based on the transfer matrix analysis, the second-order global transfer function of the interconnect network comprised of the TL driven by voltage source including its internal resistance and the impedance load is expressed. Thus, mathematical analysis enabling the physical SI-parameters' extraction was established by using the transient response of the loaded line. To verify the relevance of the developed model, RC-and RLC-lines excited by square-wavepulse with 10-Gbits/s-rate were investigated. So, comparisons with SPICE-computations were performed. As results, transient responses perfectly well correlated to the reference SPICE-models were evidenced. As application of the introduced model, evaluations of rise-/fall-times, propagation delays, signal attenuations and even the settling times were realized for different values of TL-parameters. Compared to other methods, the computation execution time and data memory consumed by the program implementing the proposed delay modeling-method algorithm are much better. © 2012 EDP Sciences. Source

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