Pulse profiling for AlGaN/GaN HEMTs large signal characterizations

Abstract-This paper deals with pulsed LSNA measurements of high power AlGaN/GaN transistors performed in a multiharmonic passive load-pull environment. Time domain waveforms are acquired during a 150 ns window. This measurement window is moved across the 20µs duration of pulses, the period is 1 ms. Phase and gain drifts of transistor characteristics versus time during the pulses are obtained and discussed

Estimation of muscle activation during different walking speeds with two mathematical approaches compared to surface EMG

Background Muscle force estimation could improve clinical gait analysis by enhancing insight into causes of impairments and informing targeted treatments. However, it is not currently standard practice to use muscle force models to augment clinical gait analysis, partly, because robust validations of estimated muscle activations, underpinning force modelling processes, against recorded electromyography (EMG) are lacking. Research Question Therefore, in order to facilitate future clinical use, this study sought to validate estimated lower limb muscle activation using two mathematical models (static optimisation SO, computed muscle control CMC) against recorded muscle activations of ten healthy participants. Methods Participants walked at five speeds. Visual agreement in activation onset and offset as well as linear correlation (r) and mean absolute error (MAE) between models and EMG were evaluated. Results MAE between measured and recorded activations were variable across speeds (SO vs EMG 15–68%, CMC vs EMG 13–69%). Slower speeds resulted in smaller deviations (mean MAE < 30%) than faster speeds. Correlation was high (r > 0.5) for only 11/40 (CMC) and 6/40 (SO) conditions (muscles X speeds) compared to EMG. Significance Modelling approaches do not yet show sufficient consistency of agreement between estimated and recorded muscle activation to support recommending immediate clinical adoption of muscle force modelling. This may be because assumptions underlying muscle activation estimations (e.g. muscles’ anatomy and maximum voluntary contraction) are not yet sufficiently individualizable. Future research needs to find timely and cost efficient ways to scale musculoskeletal models for better individualisation to facilitate future clinical implementation

Mesures de formes d'ondes temporelles en impulsions : application à la caractérisation de transistors micro-ondes de forte puissance.

Soutenue le 19 octobre 2007Thèse université de Limoge

Advanced measurements for Power Transistors

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Mesures de formes d ondes temporelles en impulsions (application à la caractérisation de transistors micro-ondes de forte puissance)

Ces travaux traitent de la mesure de formes d ondes temporelles en mode continu et en impulsions, avec comme application la caractérisation des transistors de puissance aux fréquences micro-ondes. Un banc de mesure a été développé autour du Large Signal Network Analyser. Une caractéristique importante de ce banc est la méthode de couplage, qui a été améliorée à partir d une technique localisée. Elle permet de changer les caractéristiques habituelles de couplage des signaux micro-ondes pour introduire un minimum de pertes dans le chemin de puissance micro-onde. Elle permet de mesurer jusqu à 20 GHz. Dans un deuxième temps, l ensemble des mesures du banc a été étendu en impulsions. Une méthode pour mesurer dans ce mode a été mise en place pour conserver toute la dynamique de notre système, pour des rapports cycliques descendant à 0.0001. Dans une dernière partie, l intérêt de mesurer les formes d ondes temporelles avec les performances électriques des transistors de puissance est d emontré, pour observer les zones limites d utilisation des transistors en tension et en courant. Les capacités du banc de mesures à caractériser des composants GaN de puissance ont été prouvées, avec un HEMT AlGaN/GaN Tiger mesuré à 20 W en impulsions à 2 GHz.This work deals with time domain characterization of microwave power transistors, in continuous and pulsed modes. A setup has been created with the Large Signal Network Analyser, in order to manage together the constraints of these two objectives : time domain and power characterization. For this kind of setup, a key point is the coupling method, which has used and improved localized techniques defined in the 50s. This method can improve characteristics of the classical couplers in this kind of setup, to introduce as less losses as possible in the main RF path, up to 20 GHz. The second part consists in allowing this setup s measurements in pulsed mode. A method to acquire data in this mode has been developed, in order to keep all the setup s dynamic range, even for duty cycles of 0.0001. In the last part, the interest of measuring time domain slopes with electrical performances is showed, to reach the transistor s limits in terms of voltage and current. Power capabilities of this setup have been demonstrated with a HEMT AlGaN/GaN Tiger up to 20 W at 2 GHz.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF

An electrothermal model for AlGaN/GaN power HEMTs including trapping effects to improve large-signal simulation results on high VSWR.

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A drain-Lag Model for AlGaN/GaN Power HEMTS

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