Showing papers by "Blaise Ravelo published in 2008"

Application of negative group delay active circuits to the design of broadband and constant phase shifters

Abstract: The new phase-shifter configuration described in this report uses a negative group delay (NGD) active circuit. In this topology, a classical transmission line is set in cascade with an NGD circuit whose phase slopes are alike, but opposite, to get a constant and broadband phase shift. The proposed approach was validated through the design and measurement of a phase shifter, which exhibited a constant phase of 90° ± 5° over a 75% relative bandwidth around 1.6 GHz. Moreover, as the group delay of the NGD circuit compensated the transmission line one, the overall circuit group delay was kept to a small value in the operating frequency band. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3078–3080, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23883

Application of negative group delay active circuits to reduce the 50% propagation Delay of RC-line model

Abstract: This paper presents a new method developed to reduce the propagation delay by using a negative group delay (NGD) active circuit. Analytical expressions are proposed to demonstrate the validity of our approach in the case of an RC-transmission line model. The synthesis method of NGD circuits versus the line length is detailed. For a 0.5 Gbit/s digital signal and a 2-cm-long RC-line model, time-domain simulations carried out with a high-frequency circuit simulator showed that the 50% propagation delay was reduced by 94%. Finally, potential applications of this method to compensate for time delays in different interconnect configurations (VLSI, package, on-chip, long-line, ...) are discussed.

Negative group delay active topologies respectively dedicated to microwave frequencies and baseband signals

Abstract: This paper proposes and describes in details the synthesis, design and implementation of two different active topologies exhibiting negative group delay (NGD) in differ- ent frequency bands. With the first of them, gain and NGD in microwave frequency band are simultaneously achieved; the basic cell consists in a field effect transistor (FET) cas- caded with a shunt RLC series network. The second topol- ogy brings also gain and NGD but is particularly dedicated to baseband signals; this circuit is also built with a FET; but this time in feedback with an RL series network. For both approaches, analytical formulas demonstrating the existence of gain and NGD are proposed together with details about the associated equations, at first for a single cell and then for multi-stage circuits. After implementation of each topol- ogy in a two-stage configuration, the results from experi- ments in frequency-domain are carefully compared to those from simulations; the same thing is done in time-domain for the baseband-dedicated device. Time-domain simulations and measurements highlight the high capability of both to- pologies to compensate or control various dispersive effects. Indeed for both circuits, in case of Gaussian-pulse or - modulated signal, the maximum of the output signal exhib- its a time advance compared to the input one of respectively more than 40% and 60% of the standard deviation of the input signal. Moreover, this high relative time-advance is obtained with gain and a pulse compression phenomenon.

Flow Regimes in Horizontal Viscous Dam-Break Flow of Clayous Mud

Abstract: Abstract The main characteristics of geological flows such as debris flows, avalanches and lahars is due to the relative importance of viscous versus inertial forces in the momentum balance. This paper considers the motion generated by the collapse of a dam-retaining mud, itself modeled as a power-law fluid. The equation of motion is derived in a non-dimensional form and solved analytically with the shallow-water assumption in a dry and smooth horizontal channel. Notably indicated are flow regimes and the effect of the reservoir length as well as the effect of mud rheology on flow development. Then, a parametric study of this model is produced and the effect of mud shear-thinning on flow development is pointed out.