Analytical model and design of load modulated balanced amplifier
Aras, Yunus Erdem
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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.
High-eﬃcient power ampliﬁer