Breaking the Bandwidth Limit: A Review of Broadband Doherty Power Amplifier Design for 5G

The next generation wireless network, 5G, is expected to provide ubiquitous connections to billions of devices as well as to unlock many new services through multigigabit-per-second data transmission. To meet the ever-increasing demands for higher data rates and larger capacities, new modulation schemes have been developed, and wider frequency bands, such as those at millimeter wave (mm-wave), have been designated for 5G [1], [2]. Massive multiple input/multiple output (MIMO), which uses a large number of antennas at the transmitter and receiver, has been considered one of the key 5G technologies to improve data throughput and spectrum efficiency [3]. These new application scenarios impose stringent requirements on wireless transceiver front ends and call for special considerations at the circuit and system design levels. In the transmitter, power amplifiers (PAs) should accommodate complex modulated signals, featuring a high peak-to-average-power ratio (PAPR) and a wide modulation bandwidth. Moreover, in massive MIMO arrays, PAs should maintain a high average efficiency to mitigate thermal heating issues.