This paper presents a class-D outphasing power amplier (PA) that incorporates a non-isolating balun combiner employing a 180° phase shift. Both isolating and non-isolating outphasing combiners are analyzed for signal restoration and combining eciency. The proposed non-isolating balun combiner employing the 180° phase shift was experimentally evaluated and compared with a commercial isolating Wilkinson combiner. When two constant-envelope signals derived from a 10 MHz long-term evolution (LTE) signal are applied to the inputs of the outphasing combiners, both combiners demonstrate successful signal reconstruction. The measured adjacent channel leakage ratios (ACLRs) are 47 dBc for the Wilkinson combiner and 46 dBc for the proposed balun combiner. At 6 dB power back-o (PBO), the proposed balun combiner achieves a combining eciency of 85.1%, representing an improvement of nearly 60% over the Wilkinson combiner. With a center frequency of 650 MHz, targeting 5G FR1 applications, a class-D outphasing PA was designed in a 28 nm CMOS process using the measured S-parameter data from both outphasing combiners. Simulation results show that the class-D outphasing PA incorporating the proposed balun combiner achieves a peak drain eciency (DE) of 82.9% with an output power of 17.7 dBm. At 6 dB PBO, the DE reaches 61%, which is approximately 37% higher than that of the outphasing PA using the Wilkinson combiner. Moreover, the designed outphasing PA supports broadband operation over the 360–860 MHz range.
Loading....