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Conception d'un système de caractérisation fonctionnelle d'amplificateur de puissance en présence de signaux modulés à l'aide de réflectomètres six-portes

Abstract : In general, power amplifier large signal characterization is done in presence of a continuous wave (CW) signal in order to deliver information that will reach a compromise between output power and power added efficiency (PAE). However, in modern telecommunication systems, power amplifier is excited by digital modulated signals, thus his linearity is a capital criterion for the global performance of the system. It is then important to have a large signal characterization tool allowing to measure the device performance under realistic conditions. In this work, we show the study and the implementation of a load-pull measurement system for power amplifier characterization using complex modulated signals. The output power, the power added efficiency (PAE) and the linearity can be optimized by varying fundamental load impedance and low frequency source/load impedances. These optimizations can be carried out using RF signals such as CW, CW-pulsed, multi-carried and modulated (GMSK, QPSK, QAM, etc.) signals. A multiharmonic source-pull and load-pull measurement system has been developped at the ENST. This system is based on a six-port reflectometers technique, and is capable of optimizing the output power and the PAE in CW mode. In order to use modulated signals, fast and low-cost power detectors based on non-polarised Schottky diodes have been implemented for the power measurement of six-port connections. In addition, to optimise linearity, low frequency impedance control modules have been added at the input and the output of the device under test (DUT). A MESFET power transistor has been tested in class A and AB operation in the presence of a QPSK modulated signal centered at 1.575GHz with a 1 MSps symbol-rate, and a bi-carried signal with 800 KHz separation. The measurements performed lead us to the following three conclusions. The first one is that; the Output power, the PAE, the ACPR (Adjacent Channel Power Ratio) and the third (IM3) and fifth (IM5) intermodulation product load-pull contours show that the optimal output power, PAE and linearity fundamental impedances are different. So it is necessary to find a compromise between the different performances. On the other hand, the results show that there exists a strong correlation between the ACPR and the IM3 in class A operation (not in class AB). Therefore predicting the ACPR from the IM3 seams to be a difficult task. The second one is the significant influence of low frequency source impedances for class AB operation in the saturation zone. This influence effects only the linearity (5dB on ACPR). The last conclusion is the influence of low frequency load impedances that occurs significantly in class A and AB operation. This influence is more important in class AB. For instance, we observe 5 to 20 dB variations on the ACPR. Note that the optimal impedance is not necessarly a short circuit. However these impedances have a great influence on the PAE (a variation of 10 points) and the output power (variation of 1 dB).
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Submitted on : Wednesday, September 14, 2005 - 8:00:00 AM
Last modification on : Friday, July 31, 2020 - 10:44:03 AM
Long-term archiving on: : Thursday, September 30, 2010 - 6:55:10 PM


  • HAL Id : pastel-00001368, version 1



Souheil Bensmida. Conception d'un système de caractérisation fonctionnelle d'amplificateur de puissance en présence de signaux modulés à l'aide de réflectomètres six-portes. domain_other. Télécom ParisTech, 2005. English. ⟨pastel-00001368⟩



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