M. Le Roy

Active Microwave Circuit With Negative Group Delay

In this letter, we report on the design, simulation and implementation of an active negative group delay circuit that operates at 1 GHz with a group delay and a gain, respectively, around 2 ns and 2 dB. Analytical formulas are proposed to demonstrate that the adopted topology is able to simultaneously achieve negative group delay (NGD) and gain while fulfilling active device constraints. The theoretical and simulated results are both validated by frequency measurements of a two-stage active microwave circuit.

Synthesis of Broadband Negative Group Delay Active Circuits

This paper deals with the design and synthesis of active circuits able to simultaneously produce negative group delay and gain at microwave frequencies or for baseband signals. Analytical equations show that the proposed topology meets these objectives while also satisfying active device requirements. Then, a synthesis approach is extracted and applied to design a two-stage microwave circuit, further validated by experimental results. This method is extended to the design of a four-stage baseband active circuit providing gain and negative group delay up to 600 MHz. A high relative time-advance is evidenced by time-domain simulations.

Broadband balun using active negative group delay circuit

In this paper, a broadband balun using an active circuit with negative group delay (NGD) is proposed. The unit cell of the active NGD circuit is based on a Field Effect Transistor (FET) in cascade with an RLC series network. First, a comparison between measurements of a two-stage prototype of this active topology and simulations validate the synthesis method of this innovative device. Then, thanks to the NGD circuit, a constant phase can be generated if this circuit is associated with a classical transmission line. By implementing such phase shifters into the two branches of a resistive splitter, we obtain a new balun topology. The NGD balun simulation results show a rather constant differential output phase (180degplusmn9deg), insertion losses above -2.4 dB and an excellent isolation below -59 dB for all three ports, for a bandwidth from 3.5 GHz to 5.5 GHz.

Equalization of interconnect propagation delay with negative group delay active circuits

In this paper, we propose a technique to compensate the propagation delay and losses in VLSI interconnects by using negative group delay (NGD) active circuits. This study uses the RLC models of interconnect lines currently considered in VLSI circuits. The circuit proposed here is based on a cell consisting of a Field Effect Transistor (FET) in parallel with a series RL passive network. We also describe the synthesis method to achieve simultaneousely a significant negative group delay and gain. Simulations allow us to first verify the performance of the NGD circuit and also show a restoration of the distorted signal shape as well as a reduction of propagation delay.

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

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.

A new design of microwave filters by using continuously varying transmission lines

This paper outlines a new original method for microwave filter design. A cubic spline interpolation is used to design a filter with a continuously changing profile. Then, the scattering parameters of a non-uniform transmission line with a cubic polynomial variation of its characteristic impedance are studied in detail in the frequency domain. In order to validate this method, a wideband bandstop filter consisting in a non-uniform microstrip line with continuously varying width was optimized, designed, constructed and measured.

Influence of design liquid crystal-based devices on the agility capability

This article deals with liquid-crystal-based tunable components: phase-shifters and patch-antennas. It reports on investigations about the influence of design on their characteristics. For phase-shifters based on an inverted microstrip line, the line design is paramount for improvement of phase-shift and figure-of-merit. Moreover, the use of liquid crystal in the design of patch antennas allows adjustment of the resonance frequency, and slot insertion results in size reduction with no decrease of performances. Both cases highlight the interest of liquid crystal in millimeter frequency devices.

Novel circuit models of arbitrary-shape line: application to parallel coupled microstrip filters with suppression of multi-harmonic responses

Following a hierarchical approach, several models are built in microwave-circuit design software to simulate and design many configurations of arbitrary-shape line. The global shape is controlled by a cubic spline interpolation; our purpose is, indeed, to make easier the handling of nonuniform structure for microwave device designers. To illustrate the potentialities of these new components, we designed a third-order bandpass coupled-line filter at 5.5 GHz. A sinusoidal strip-width perturbation is applied by using the new model of nonuniform symmetrical coupled-line. Associated to over-coupling of the resonator end, the first three spurious passbands are then suppressed.

Pulse compression with superluminal group velocity in 1-D photonic bandgap coplanar waveguide

We report on the analysis and design of a Photonic BandGap coplanar waveguide (CPW) that jointly exhibits pulse compression and superluminal group velocity in the so-called anomalous dispersion region for a Gaussian modulated signal. The coupling of an analytical analysis method with an optimization algorithm enables the design of a coplanar PBG to reach the specified function. Measurements confirm our simulation data and the relevance of our approach. Further to these experiments, a discussion on snperlnminal velocity fundamentals is proposed.

Microstrip back-cavity Hilbert Fractal Antenna for experimental detection of breast tumors

This paper presents a miniaturized microstrip back-cavity Hilbert Fractal Antenna specifically designed for breast cancer detection. This antenna is used to investigate on the possibility of detecting the presence of breast tumors by directly measuring the shift of the antenna resonance frequency. First, simulations are performed on a multi-layer breast model; then the proposed approach was applied for in vivo measurements on two different patients diagnosed with breast cancer, followed by ex vivo characterization of the electrical properties of excised tumors.