Digital Shaping and Linearization of a Dual-Input Load-Modulated Balanced Amplifier

This paper presents shaping and linearization techniques to trade-off linearity and power efficiency in a dual-input pseudo-Doherty load-modulated balanced amplifier (PD-LMBA). The proposed shaping function is defined to operate in the frequency domain and it is oriented at exploiting the dual-input architecture of the PD-LMBA to either enhance linearity or power efficiency. In addition, since the linearity requirements are not met by simply shaping the input signals, digital predistortion (DPD) linearization is applied on top of it. Experimental validation of the proposed shaping function and DPD linearization is provided for a PD-LMBA excited with 200 MHz bandwidth 5G-like modulated signals with 8 dB of PAPR. For an output power around 40 dBm, the PD-LMBA presents a power efficiency around 50%, while meeting the linearity specs of -45 dB of adjacent channel power ratio (ACPR) and error vector magnitude (EVM) below 3%.

I. Introduction

In the quest for power efficient amplification of RF communications signals, several power amplifier (PA) topologies have been proposed in the literature to be able to keep high efficiency figures over wide bandwidths and high power back-off levels. Dual-input PAs, such as the load modulated balanced amplifier (LMBA) [1], can take advantage of the additional degrees of freedom offered by the separate inputs to trade-off linearity and average efficiency. In a dual-input LMBA, e.g., [2], one of the RF signals is amplified by the balanced power amplifier pair biased in class AB, while the other RF signal excites the control power amplifier (typically biased in class C) to perform the load-modulation.