Design of Generalized Doherty Power Amplifier Including Device Parasitics Compensation With Modulated Signal Measurements

In this article, the design of a 50W symmetry Doherty Power amplifier (DPA) with an Output Power Back-Off (OPBO) extended beyond 6 dB for N78 band 5G applications is demonstrated. The challenges encountered throughout the design phase, particularly dealing with high frequency and power, including device non-idealities, are analyzed. Parasitic compensation addresses key DPA issues, such as RF current leakage from the main to the auxiliary path when the auxiliary PA is not ideally open. The fabricated DPA has been tested with a continuous wave (CW) signal, and the measured gain and Drain Efficiency (DE) were observed as 8~8.5 dB and 40.7~43%, respectively, over 3.3~3.7 GHz at 39-dBm average power (8 dB OPBO). To test the DPA’s linearity performance, a 10 MHz 64-QAM signal has been transmitted through the DPA over 3.3 ~ 3.7 GHz at 8 dB OPBO with and without digital pre-distortion (DPD). After linearization, it is observed from the measurements that the Adjacent Channel Power Ratio (ACPR) and the Error Vector Magnitude (EVM) have been enhanced to 49 dBc and 0.98%, respectively.