A de-cresting technique for polar transmitters using Envelope-Tracking (ET) and SiGe power amplifiers for mobile-WiMAX

A decresting algorithm for mobile WiMAX has been developed using time domain clipping and filtering processes for a polar transmitter (TX) using Envelope-Tracking (ET) and a monolithic SiGe power amplifier (PA). RF/Analog/Digital system and circuits co-design simulations have been performed for mobile WiMAX with 64 QAM OFDM modulation format. It is found that higher power-to-average ratio (PAR) decresting can improve the adjacent channel power ratio (ACPR) and the overall TX system efficiency, but at the cost of its EVM degradation. Our system simulations show that careful design of signal decresting can improve the overall polar TX system efficiency from 28.1% to 30.3% while the TX output can still meet the stringent WiMAX TX mask and EVM specs.

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