Filter Design Methodology and Application of GaN HEMTs in High-Frequency DC/DC Converter

ABSTRACT

Optimization of the radio frequency (RF) transmitter performance in envelope tracking (ET) and envelope elimination and restoration (EER) techniques directly implies optimization of the envelope amplifier (EA) design. Since EA should have fast dynamic response together with high efficiency, synchronous buck is a suitable topology for this kind of application. The key issues for optimization of the converter design are the characteristics of the switching devices, the LC filter design, and the driving circuit for the switches. In this paper, design optimization of the LC filter for sinusoidal output voltage together with new technological solution for switching devices based on gallium nitride is proposed, while the applied drivers are commercially available ones, suitable for aforementioned GaN switches. Design of the output filter in synchronous buck converter for high-frequency application is important from two points of view: the first one is sufficient attenuation of the unwanted harmonics of the switching frequency so that envelope reference has minimum level of distortion and the second one is the overall impact of the filter design on the converter's efficiency. In order to increase the efficiency, the LC filter should be designed in a way to obtain compromise between the conduction and switching losses of the buck converter. In the case of sinusoidal output voltage, filter design parameter has been defined as the ratio between the maximum values of the inductor current and load current and power losses dependence on this parameter has been obtained. Theoretically obtained optimum design has been confirmed through experimental measurements, where four different designs were built and tested. On the other hand, application of new switching devices based on gallium nitride provided significant efficiency enhancement in comparison to Si MOSFETs and laterally diffused MOS transistors, due to the lower values of the gate charge and on-resistance. Tests with 64QAM and wideband code division multiple access (WCDMA) RF signals showed that these devices are the best choice for this kind of application, where the main challenge is to increase the efficiency of the signal transmission simultaneously with the bandwidth.

Keywords:

• ET
• EER
• Envelope amplifier
• GaN HEMTs
• Wide large signal bandwidth
• High efficiency

Additional information

Notes on contributors

D. Cucak

Dejana Čučak received an MS degree from the University of Belgrade, Faculty of Electrical Engineering, Serbia, in 2009. She received an MS degree in industrial electronics from the University of Madrid, Spain, in 2011. Currently, she is a PhD student in Centro de Electronica Industrial (CEI), Madrid. Her research interests include modelling of wide band-gap devices, RF circuit design, and switching mode power supplies.

M. Vasic

Miroslav Vasić was born in Serbia in 1981. He received an MS degree from the University of Belgrade, School of Electrical Engineering, Serbia, in 2005. He received his MS and PhD degrees in industrial electronics from the University of Madrid, Spain, in 2008 and 2010, respectively. Since 2010, he has been working as a researcher in Centro de Electronica Industrial (CEI), Madrid. His research interests include switching mode power supplies, RF circuit design and digital control applied to power electronics.

O. García

Oscar Garcia (M’99) was born in Madrid, Spain, in 1968. He is a Full Professor at Universidad Polittecnica de Madrid. He has been involved in more than 70 research projects, holds 8 patents and he has published more than 150 technical papers in conferences and journals. He is vice-president of the Center for Industrial Electronics (CEI - UPM). Prof. Garcia received the UPM Research and Development Award for Faculty less than 35 years in 2003 and the UPM Innovation in Education Award in year 2005.

J. Oliver

Jesus A. Oliver (M’00) received his MS and PhD degrees in electrical engineering from Universidad Politecnica de Madrid, Madrid, Spain in 1996 and 2007, respectively. Since 2001, he has been an assistant professor of electrical engineering at Universidad Politecnica de Madrid and in 2007 he became associate professor. He has published over 100 technical papers and holds three patents. He has been actively involved in over 60 R&D projects for companies in Europe, USA, and Australia.

P. Alou

Pedro Alou (M’ 07) was born in Madrid, Spain in 1970. He received his MS and PhD degrees in electrical engineering from the Universidad Politecnica de Madrid (UPM), Spain, in 1995 and 2004, respectively. He has been a professor at UPM since 1997. He has been involved in power electronics since 1995, participating in more than 40 R&D projects with industry. He has authored or co-authored over 100 technical papers and holds three patents.

J. A. Cobos

José A. Cobos has been a professor at the Technical University of Madrid (UPM) since 2001. His contributions are focused in the field of power supply systems. His research interests include energy efficiency in microprocessors and RF amplifiers, magnetic components, piezoelectric transformers, and dynamic power management. He received the “UPM Research and Development Award for faculty less than 35 years of age”, and the “Richard Bass Outstanding Young Power Electronics Award of the IEEE” (year 2000). He has advised 14 Doctoral dissertations, published over 200 technical papers and holds 6 patents. He received the Semikron Innovation Award for the teamwork on “RF Power Amplifier with Increased Efficiency and Bandwidth”. He is the Director of the CEI-UPM, a university research centre, leading a strong industrial programme in power electronics, with technology transfer through more than 50 direct R&D contracts with companies in Europe, USA, Australia, and China. The CEI-UPM was awarded among the top five European universities by the EPSMA in 2007, and awarded with the “UPM Technology transfer award” in 2006.