Equivalent load impedance of pulse width modulation excited band pass filters |
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Authors: | David Seebacher Peter Singerl Christian Schuberth Michael E. Gadringer Wolfgang Bösch |
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Affiliation: | 1. Institute of Microwave and Photonic Engineering, Graz University of Technology, Graz, Austria;2. Infineon Technologies Austria AG, RF Power Department Villach, Austria |
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Abstract: | Many efficiency enhancement concepts for power amplifiers (PAs) rely on pulse width modulation in combination with direct filter connection. Direct connection of bandpass filters results in load modulation for the PA. Therefore, the resulting equivalent impedances, respectively, load trajectories, are important for efficient operation. This article presents analytical equations to calculate these equivalent load impedances. The equations are parameterized with two impedance values making them independent of the filter structure. Based on the presented equations a PA design properly taking the load modulation into account can be done. This is shown based on a design example of a biphase energy recovery transmitter, verifying the general validity of the equations. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:164–172, 2015. |
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Keywords: | baseband pulse width modulation high efficiency microwave power amplifiers switching amplifiers energy reuse direct filter connection equivalent load impedance |
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