Riadh Essaadali

A Reliable Model Parameter Extraction Method Applied to AlGaN/GaN HEMTs

In this paper, a reliable small-signal model parameter extraction method for GaN high electron mobility transistor (HEMT) on Si substrate has been developed and validated with respect to different gate width devices. The main advantage of this approach is its accuracy and dependency on only pinched-off and unbiased S-parameter measurements. The developed procedure shows reliable and physically relevant results for the investigated devices and scaled with the gate width. A very good agreement is obtained between small-and large-signal simulations and measurements of the considered GaN HEMTs.

A New GaN HEMT Equivalent Circuit Modeling Technique Based on X-Parameters

In this paper, a new accurate small-and large-signal equivalent-circuit-based modeling technique for gallium nitride (GaN) HEMT transistors grown on silicon substrate is presented. Despite X-parameters are developed as tools for the development of black-box modeling, they are used for equivalent-circuit-based model extraction. Unlike traditional modeling that uses the small-signal data to build with an indirect manner a nonlinear model, the proposed model is extracted from X-parameter measurements directly. However, similar to the equivalent-circuit-based models discussed in the literature, the new model is subdivided into extrinsic and intrinsic parts. The extrinsic part consists of linear elements and is related to the physical layout of the transistor. The intrinsic part can be extracted with the proposed analytical de-embedding technique. The nonlinear intrinsic elements are represented by new nonlinear lumped impedances and admittances whose extraction is carried out using a newly proposed technique. This new technique uses nonlinear network parameters, various X-parameter conversion rules, and basic analysis techniques of interconnected nonlinear networks. It is accurate and more advantageous than traditional transistor modeling techniques. The modeling procedure was applied to a 10 μm × 200 μm GaN HEMT with a gate length of 0.25 μm. A very good accordance between model simulations and measurements was obtained, validating the modeling approach.

A new simple Unmanned Aerial Vehicle doppler effect RF reducing technique

The purpose of this paper is to present a solution to reduce the Doppler effect in wireless communication systems. As distance increases, pathloss increases too and the signal to noise ratio decreases. A major problem that affects the quality of the link is the horizon. A solution to improve signal quality is to use an Unmanned Aerial Vehicle (UAV) relaying far mobile stations to the base station. However, because of UAVs speed, Doppler frequency shift decreases the signal to noise ratio and cannot be supported by the base station for the values that are higher than the measured limit. The simple solution explained in this paper reduces dramatically the Doppler effect and makes possible the use of UAVs, as a repeater, to extend the communication even at high speed.

A general and reliable model for GaN HEMTs on Si and SiC substrates

In this paper a reliable and cost-effective modeling approach for GaN HEMT on both Si and SiC substrates is presented. The developed model is validated in terms of small-and large-signal simulations for 2-mm GaN-on-Si and 1-mm GaN-on-SiC HEMTs.

Modeling of extrinsic parasitic elements of Si based GaN HEMTs using two step de-embedding structures

A new parasitic elements extraction technique for GaN HEMT transistors on Si substrate is presented. This technique is based on the use of two de-embedding GaN structures: open and thru-short. The equivalent circuit models along with the extraction procedure are detailed. A very good agreement between measurements and simulations validate the developed extraction method.

Optimization of a direct conversion multi-standard transmitter used for rescue operations

A new direct conversion architecture design of a multi-standard transmitter supporting cellular standards (GSM, UMTS and Wimax), wireless personal and local area network standards (Bluetooth, Zigbee and IEE802.11 b/g) as well as Radio navigation standards (GPS, Galileo) is presented in this paper dedicated for rescue applications. Behind this high number of standards, the proposed optimization design technique was introduced to reduce the cost, size and weight of the transmitter part.

Overwater point-to-multipoint radio pathloss characterization and modeling

This paper presents experimental results of overwater radio path loss in the 4.4 to 5.0 GHz band. These measurements involve horizontal and vertical polarizations. Based on electromagnetic theory, a deterministic two ray model that mimics measurements is developed. The model can predict the received power level for all distances lower and higher than the critical distance. The model is consistent with measurements in MIMO modes using any kind of linear polarized antennas.

Improving RFID tag detection in the presence of mechanical vibration

This paper discusses the mechanical vibration effect of metal structure on RFID and presents a solution to circumvent it. The transmission link between a tag and RFID reader is affected by induced current issued from magnetic coupling. This interference affects mainly the performances of the RFID reader. A new practical technique that avoids the resulting coupling interference is presented in this paper. The RFID system is analyzed at low frequency to provide a new solution that answers to the requirements of industrial applications according to ISO standards. The RFID readers antenna is accurately simulated with EMWorks software under different environment magnetic conditions in order to identify the main source of interference problem. Experimental results validate the solution presented in this paper and prove its enhanced performances.

AIS data exchange protocol study and embedded software development for maritime navigation

The AIS is one among the standards of radio communication system to be approved in the whole of the maritime environment. The adoption of AIS technology as a radio data maritime network that hopes for the rise of added values to the services of maritime industry allowing not only the safety of the ships and the environmental protection, but also improving the organization of the ports and the operations. The goal of this work consists on implementing the protocol layers of mobile AIS station on a DSP by using an embedded operating system: Visual DSP kernel. The solution comprises embedded software for both class A and class B AIS mobile equipment that can use CSTDMA or SOTDMA.

Selective orthogonal predistortion for power amplifiers

Many factors could be considered to produce spectral regrowth in communications systems as well as the nonlinearity of power amplifiers. This paper proposes a novel reduced complexity dual band power amplifier (PA) digital predistortion. A new approach that is based on orthogonal polynomials is presented to overcome the limits of the nonlinear compensation using power series inverses. Its main properties and operational conditions have been detailed with the theory of orthogonal polynomial models. The proposed compensation technique provides an intuitive means of spectral regrowth analysis, and high accuracy tool.