Line-up efficiency improvement using dual path Doherty power amplifier

In this paper, we demonstrate for the first time, a transmitter lineup consisting of a multi-stage dual path asymmetrical Doherty power amplifier (PA) with an innovative method to condition the phase and amplitude of the input signals presented to the Carrier and Peaking amplifiers to achieve optimum performance. The final stage PA has been designed using a new generation of Freescale Airfast™ LDMOS power transistors. Asymmetrical Doherty PA using this transistor shows more than 15.5 dB gain and 48% efficiency at 8 dB output back-off (OBO). Additionally in dual path configuration a line-up efficiency of greater than 43% at 8 dB OBO is achieved. The corrected adjacent channel power ratio (ACPR) values are better than -52 dBc after digital pre-distortion (DPD) for a wideband LTE signal. The amplifier line-up targets next generation cellular infrastructure systems operating in the 2.6 GHz band, and to the authors knowledge, exhibits the highest reported line-up performance for this application.