Improvements in high power LDMOS amplifier efficiency realized through the application of mixed-signal active loadpull

This paper presents the results of experimental large-signal characterization of a high power LDMOS amplifier using a mixed-signal active load pull system. The architecture of the system provides the freedom to present unique and independent reflection coefficients at multiple different frequencies. In this case the fundamental frequency, and the 2nd harmonic frequency were chosen, and the reflection coefficients presented to the output terminal of the transistor were captured at these two frequencies. A high voltage LDMOS power amplifier from Freescale Semiconductor was studied and the results will demonstrate that a distinct improvement in drain efficiency is realized through careful magnitude and phase selection of the reflection coefficient at the 2nd harmonic frequency while keeping the refection coefficient presented at the fundamental frequency at a constant optimized value.