A Multilevel Pulse-Modulated Polar Transmitter Based on a Doherty Power Amplifier and Memoryless Digital Predistortion

This letter presents an aliasing free multilevel pulse modulation (MLPM) architecture to implement a linear Doherty power amplifier (PA). This letter is believed to be the first reported results of this type of Doherty architecture to achieve linear amplification rather than the usual situation of a continuous amplitude modulated carrier and continuous load modulation. Our results show that both high efficiency and good linearization can be achieved with simple memoryless digital predistortion. Doherty operation with MLPM is believed to have benefits in linearization due to the MLPM discrete drive as less power is dissipated by the PA, leading to less thermal-related memory effects. A prototype transmitter system is constructed using a commercially available Doherty PA for validation. Measurements are performed using a 64-QAM long-term evolution (LTE) downlink signal at 2140 MHz with 20-MHz bandwidth. The overall system achieved an output power level of 40.1 dBm with a power-added efficiency of 39.5% while passing the -45-dBc downlink spectral requirements of the LTE standard.