A Novel Timing Synchronization Method for MIMO-OFDM Systems

International audienceTo increase the throughput of transmission systems,MIMO-OFDM technology enables better transmission rateand improves the reception. The synchronization between thetransmitter and the receiver has become a big challenge. A badtiming synchronization causes the loss of a lot of informationin a MIMO-OFDM system. In this paper, a novel timingsynchronization method is proposed for a MIMO-OFDMsystems with Nt transmit antennas and Nr receive antennas.The proposed method is based on transmit an orthogonalCAZAC sequences over different transmit antennas [1].Simulations results show that the proposed solution presentsa good performance at a low SNR (Signal to Noise Ratio) inAWGN and multipath fading Rayleigh channels, where DopplerEffect is not considered for current simulations. Furthermore,this method can be implemented for MIMO-OFDM system upto 8 × 8 as well. In the proposed method, the coarse and finetiming synchronization are done at the same time at each receiveantenna due to the different training sequences transmitted overdifferent transmit antenna

Robust Timing Synchronization Preamble for MIMO-OFDM Systems Using Mapped CAZAC Sequences

International audienceThe paper proposes a time and frequency synchronizaton algorithm for MIMO-OFDM systems.This algorithm designed a training sequence that based on CAZAC sequence,it has sleep timing measuring function waveform,it shows satisfactory performance of delay estimation of each antenna.Simulation results indicate that this timing synchronization algorithm shows satisfactory performance in Rayleigh and AWGN channel at a low signal-to-noise ratios(SNR)

A solution for channel electron migration in normally-off MIS-HEMT with buried fluorine ions

International audienceHigh electron mobility transistors based on Gallium Nitride are promising devices for high frequency and high-power applications. While switching applications demand normally-off operation, conventional HEMTs possess a channel populated with electrons at zero gate voltage making them normally-on. By implanting fluorine below the channel, normally-off operation can be achieved. However, at high gate voltages, a drop in the transconductance is obtained due to electron migration from the AlGaN/GaN interface to the insulator/AlGaN interface. In this work, to recover the drop in the transconductance and hence increase the current density, an AlN interlayer is introduced between the AlGaN and GaN layers to block electron migratio

Localized buried P-doped region for E-mode GaN MISHEMTs

International audienceA new design for an enhancement mode Gallium Nitride based high electron mobility transistor is proposed along with a novel fabrication technique. Normally-off operation is achieved through the introduction of a localized p-region below the AlGaN/GaN interface underneath the gate electrode. Since achieving high hole concentration through ion implantation is experimentally challenging, the effect of a localized buried p-region was replicated through the growth of an epitaxial p-layer in which N-wells will be later introduced. Simulation results conducted under ATLAS, a TCAD simulation tool from Silvaco, demonstrated a successful shift of the threshold voltage to positive values. The physics behind this shift is explained through the band diagram. A sensitivity analysis is conducted showing the effect of device parameters on the threshold voltage and the current density

Localized buried P-doped region for E-mode GaN MISHEMTs

International audienceA new design for an enhancement mode Gallium Nitride based high electron mobility transistor is proposed along with a novel fabrication technique. Normally-off operation is achieved through the introduction of a localized p-region below the AlGaN/GaN interface underneath the gate electrode. Since achieving high hole concentration through ion implantation is experimentally challenging, the effect of a localized buried p-region was replicated through the growth of an epitaxial p-layer in which N-wells will be later introduced. Simulation results conducted under ATLAS, a TCAD simulation tool from Silvaco, demonstrated a successful shift of the threshold voltage to positive values. The physics behind this shift is explained through the band diagram. A sensitivity analysis is conducted showing the effect of device parameters on the threshold voltage and the current density

P-doped region below the AlGaN/GaN interface for normally-off HEMT

International audienceDevelopment of a new design for enhancement-mode AlGaN/GaN HEMT is presented. The normally-off operation was achieved by burying a p-GaN region below the AlGaN/GaN interface only below the gate. Simulation results show that the proposed technique is capable of shifting the threshold voltage to positive values, making the HEMT normally-off. To address the advantages and drawbacks of the proposed structure a comparison with the normally-off Gate injection transistor (GIT) was performed. The proposed structure seems to be more effective when it comes to the p-doping concentration required to achieve normally-off operation and offers superior confinement for the two dimensional electron gas. On the other hand, the low forward gate voltage limits the increase of the threshold voltage

Un interrupteur GaN HEMT normally-off grâce à des ions fluor implantés sous l'interface AlGaN/GaN

National audienceAlGaN/GaN HEMTs are very promising candidates for high frequency applications with high power and low noise. Unfortunately, while switching applications strongly demand normally-off operation, conventional HEMTs are normally-on. For the sake of achieving normally-off HEMTs, several structures have been proposed. One of the major normally-off HEMTs uses fluorine implantation in the AlGaN layer. We suggest in this work the implantation of fluorine ions under the AlGaN/GaN interface only below the gate electrode rather than implanting in the AlGaN layer. Simulation results show that the proposed method is capable of achieving normally-off operation and more effective when it comes to the fluorine concentration required to obtain the desired threshold voltage. Neither the vertical breakdown voltage, nor the off-state current are affected by this approach.Les HEMTs en AlGaN/GaN sont des candidats prometteurs pour les applications forte puissance, haute fréquence et faible bruit. Grâce au champ électrique critique élevé du GaN et à la haute mobilité électronique dans le gaz bidimensionnel (2DEG) du HEMT, ce composant peut afficher des tenues en tension et des fréquences de commutation élevées ainsi que des résistances à l'état passant faibles, dépassant ainsi les limites des composants conventionnels en silicium. Alors que les applications de commutation de puissance nécessitent très souvent des composants normally-off, les HEMTs conventionnels ont un fonctionnement normally-on. C'est pourquoi plusieurs structures de HEMTs normally-off ont été proposées récemment dans la littérature, l'une d'entre elles utilisant l'implantation de fluor dans la couche d'AlGaN. Dans ce travail, nous suggérons d'implanter les ions fluor non pas dans l'AlGaN mais dans la couche de GaN, sous l'interface AlGaN/GaN et seulement sous l'électrode de grille. Les résultats de simulations montrent que la méthode proposée permet d'obtenir un fonctionnement normally-off. En outre, cette méthode semble être plus efficace, notamment en terme de concentration du fluor implanté, qui est le paramètre d'ajustement permettant d'obtenir la tension de seuil souhaitée

Scalable normally-off MIS-HEMT using Fluorine implantation below the channel

International audienceA new normally-off Metal-Insulator- Semiconductor High-Electron-Mobility-Transistor (MIS-HEMT) is proposed. The design is based on the implantation of fluorine ions in the GaN layer below the gate electrode under the AlGaN/GaN interface. Sensitivity analyses are carried out, showing the effects of the fluorine concentration and the thickness of the insulator on the threshold voltage. The limitations and scalability of this technique are pointed out

HEMT with fluorine implanted below the AlGaN/GaN interface for normally-off operation

2 pagesInternational audienceAlGaN/GaN HEMTs are promising candidates for high frequency applications with high power and low noise. While switching applications demand normally-off operation, conventional HEMTs are normally-on. To achieve normally-off HEMTs, several structures have been proposed. One of the major normally-off HEMTs uses fluorine implantation in the AlGaN layer. We suggest in this work the implantation of fluorine ions under the AlGaN/GaN interface only below the gate electrode rather than implanting in the AlGaN layer. Simulation results show that the proposed method is capable of achieving normally-off operation and is more effective when it comes to the fluorine concentration required to obtain a desired threshold voltag