Speaker
Professor Patrick Roblin, The Ohio State University, Columbus, Ohio
Topic
Design of Doherty and Chireix Power Amplifiers Using an Embedding Device Model
Abstract
The design specs for front end power amplifiers (PA) in cellular phone base stations are becoming more stringent. Spectral efficient OFDM modulation schemes such as LTE (long term evolution) lead to signals with large peak to average power ratios (7-12 dB). Also 4G base stations continue to evolve toward broader bandwidth and PA must be designed to support contiguous or non-contiguous multiband operation.
To implement broadband PAs which are both linear and power efficient, modern base stations presently rely on the Doherty architecture. A Doherty PA (DPA) combines two or more PAs to optimize the power efficiency at the average and peak powers. DPAs can exhibit an average efficiency around 50% for single-band LTE signals. To optimize the power efficiency of the main and peaking PAs used in DPA , specific optimal internal modes of operation are usually targeted at the device current-source reference planes. To do so a tremendously large search space for the multi-harmonic input and output impedance terminations must then be simultaneously explored using load pull to achieve the targeted waveform engineering over the band of interest. Recently a new paradigm in PA design has emerged which allows the designer to bypass this blind search. When a nonlinear embedding device model is used, the PA designer can in a single simulation for each power level, predicts from the desired internal mode of operation at the current source planes, the amplitude and phase of the multi-harmonic incident waves required at the transistor package reference planes. This approach which greatly assists with the DPA design requires that a reasonably accurate device model be available. The validity of the model synthesis can then be checked using NVNA measurements to verify that the deembedded data and the simulated results are consistent at the current source reference planes. Examples of such designs for Doherty and Chireix amplifiers will be presented.
Speaker's biography
Patrick Roblin received the Maitrise de Physique degree from the Louis Pasteur University, Strasbourg, France, in 1980, and the D.Sc. degree in electrical engineering from Washington University, St. Louis, MO, in 1984. In 1984, he joined the Department of Electrical and Computer Engineering at The Ohio State University (OSU), Columbus, OH where he is currently a Professor. His present research interests include the measurement, modeling, design and linearization of non-linear RF devices and circuits such as power-amplifiers, oscillators and modulators. He authored and co-authored two textbooks published by Cambridge University Press. He is the founder of the Non-Linear RF research lab at OSU. He has developed at OSU two educational RF/microwave laboratories and associated curriculum for training both undergraduate and graduate students.