Analytical model and design of load modulated balanced amplifier
Date
Authors
Editor(s)
Advisor
Supervisor
Co-Advisor
Co-Supervisor
Instructor
Source Title
Print ISSN
Electronic ISSN
Publisher
Volume
Issue
Pages
Language
Type
Journal Title
Journal ISSN
Volume Title
Series
Abstract
RF power amplifiers (PA) with high efficiency and linearity are in high demand for modern communication systems. Modulated signals having a high peakto-average power ratio (PAPR) require PA’s to maintain these features in the output-back-off (OBO) region. Since higher linearity always brings the trade-off in the form of lower efficiency, a PA having both high efficiency and linearity is challenging requirement for RF designers. Load modulation is one of the promising techniques offering good efficiencylinearity trade-off under OBO conditions for conventional PAs. This work presents an analytical model for the load modulated balanced amplifier (LMBA) using the recently introduced analytical non-linear model of a RF power transistor. We show that it is possible to predict the efficiency and nonlinearity of the LMBA reasonably well using this simple transistor model having only a small number of parameters. To test the performance of the analytical model, we designed an LMBA using three identical discrete RF transistors and 3-dB hybrid couplers. The model parameters of the 5-W GaAs PHEMT are determined from the I-V characteristics and load-pull measurements. LMBA works at 1.7 GHz with a peak output power of 37.5 dBm and with a peak efficiency of 53%. The efficiency is measured to be 47% at 6 dB output-back-off.