Philippe Bouysse

40-GHz/150-ns versatile pulsed measurement system for microwave transistor isothermal characterization

A versatile pulsed I(V) and 40-GHz RF measurement system is described with all the know-how and methods to perform efficient, safe, and reliable nonlinear transistor measurements. Capability of discrimination between thermal and trapping effects with a pulse setup is demonstrated. Capture and emission constant times of trapping effects are measured. A method to electrically measure the thermal resistance and capacitance of transistors with a pulse setup is proposed.

Two-Stage GaN HEMT Amplifier With Gate–Source Voltage Shaping for Efficiency Versus Bandwidth Enhancements

In this paper a two-stage 2-GHz GaN HEMT amplifier with 15-W output power, 28-dB power gain, and 70% power-added efficiency (PAE) is presented. The power stage is designed to operate under class F conditions. The driver stage operates under class F-1 conditions and feeds the power stage with both fundamental and second harmonic components. The inter stage matching is designed to target a quasi-half sine voltage shape at the intrinsic gate port of the power stage. The goal is to reduce aperture angle of the power stage and get PAE improvements over a wide frequency bandwidth. In addition to the amplifier design description, this paper reports original time-domain waveform measurements at internal nodes of the designed two-stage power amplifier using calibrated high-impedance probes and large signal network analyzer. Furthermore, waveform measurements recorded at different frequencies show that aperture angle remains reduced over large frequency bandwidth. In this study, a PAE greater than 60% is reached over 20% frequency bandwidth.

Low frequency parasitic effects in RF transistors and their impact on power amplifier performances

In this paper Low Frequency (LF) parasitic effects are assessed through three kinds of measurements. It is shown that LF S-parameters measurements allow to extract the thermal impedance of Heterojunction Bipolar Transistors (HBTs) and to put dispersive effects of AlGaN/GaN High Electron Mobility Transistors (HEMTs) into evidence. Large signal (RF pulsed and two tone intermodulation) confirm the impact of those parasitic effects on performances of Power Amplifiers.

A measurement set-up and methodology combining dynamic biasing and baseband predistorsion for high efficiency and linear amplifier design

This paper presents a time domain envelope measurement system that enables the study and the optimization of high efficiency and linear power amplifiers by applying both envelope tracking and digital base band predistorsion techniques. A man focus of this paper is the description of the set up architecture along with its capability to achieve in depth investigations on the dynamic behavior of envelope tracking amplifiers (ET PAs). To reach optimal efficiency and linearity performances ET PAs need to be accurately characterized under dynamic operating conditions in order to perform a well suited control of RF input envelope and Was voltage tracking signals. The proposed set up is applied here to a 10 W GaN Power amplifier from Cree at 3.6 GHz

Analysis of the Doherty technique and application to a 900MHz power amplifier

In this paper, we present the study, the realisation and the measurement of an amplifier at 900 MHz using the Doherty technique. This technique is based on the large signal performance analysis of the active devices under different drive levels. The improvements made by the application of this technique were checked by simulations and measurements on a prototype made with two MESFETs transistors. For a 6 dB backoff, obtaining significant values of Power Added Efficiency was possible thanks to the application of a methodology of design, specific to this technique.

A new design approach of high efficiency S-band 25 W mixerless power modulator based on high voltage 50V GaN-HEMT technology

In this paper, a novel concept for efficient and wideband, S band - 25W power modulator designed by taking the advantages of high voltage (50V) GaN HEMT technology is reported. The main objective of this study is to demonstrate the interest of merging both amplitude modulation and power amplification functions without the use of mixer in order to get high efficiency performances (>45%). To fully validate this principle, a two-stage power modulator circuit has been fabricated and tested. It delivers an output modulated (AM) power wave to a 50 Ω load and is based on a variable gain control principle with switched saturated states operating always at maximum Power Added Efficiency (PAE). PAE of around 45 % over 400 MHz RF bandwidth is achieved. With a fixed input power (CW) of 19 dBm, >10 dB output power range is obtained corresponding to 15V to 45V drain bias control, with 2.5 W and 25 W RF output powers respectively.

Potentialités des séquences d’étalement chaotiques pour l’amélioration duTEEB d’un systèmeDS-CDMA asynchrone

RésuméL’utilisation de séquences chaotiques comme séquences d’étalement de spectre dans un système de communication à accès multiple à répartition par les codes (Direct Sequence-Code Division Multiple Access) est présentée. La simulation du système de transmission est réalisée avec le logiciel Omnisys. Les séquences d’étalement chaotiques sont générées par une équation non-linéaire récursive. Le taux d’erreur par élément binaire du système proposé est comparé à celui obtenu sur ce même système utilisant des séquences binaires de Gold. Les résultats montrent qu’il existe des séquences chaotiques permettant d’améliorer les performances du système en terme de nombre d’utilisateurs.AbstractThe use of chaotic sequences as spectral spreading sequences in a Direct Sequence-Code Division Multiple Access is proposed in this paper. The simulation of the system is performed with the system simulator Omnisys. The chaotic spreading sequences are generated from a non-linear recursive equation. The Bit Error Rate of this system is compared with theBER of the same system using binary Gold sequences. The results show that chaotic sequences can improve performances in terms of allowable number of users.

High speed and highly efficient S-band 20 W mixerless vector power modulator

This paper presents a performance evaluation of an original highly efficient and linear GaN-HEMT Vector Power Modulator (VPM) based on the design of a two-stage saturated variable gain (SVG) amplifier and a multi-level discrete supply modulator (SM). The proposed novel architecture for transforming a digital baseband data stream into an RF Vector modulated power waveform (RF Power DAC) is validated using a specific laboratory test bench. The main objective of this study is to merge signal modulation and DC to RF energy conversion functions into a single and compact GaN based mixer-less circuit. Using high-voltage 50 V GaN technology, a 20 W S-band vector power modulator having overall average PAE of around 40 % is reported. The concept demonstrator is experimentally validated up to 100 Msymbols/sec 16-QAM modulation scheme. Functional time alignment with phase and amplitude compensation procedure focusing on measured constellation at 40 Msymbols/sec enables to reach excellent EVM performances of around 3.2 %.