Theoretical and Experimental Analysis of Reversed Uneven Power Splitting Technique in GaN MMIC Doherty Power Amplifiers

Abstract

We present a theoretical and experimental analysis of the use of a reversed uneven power splitting (RUPS) technique for asymmetric Doherty power amplifiers (PAs). The RUPS technique utilizes an uneven power splitter that drives more input power into the carrier amplifier, enabling shallow class-C operation of the peaking amplifier. Although the RUPS technique has played a significant role in achieving high-performance Doherty PAs, there has been a lack of comprehensive research examining the fundamental factors that contribute to its effectiveness. We conducted numerical and experimental investigations to demonstrate that the RUPS Doherty PA exhibits significant improvements in efficiency, gain, and linearity compared to conventional Doherty PAs with even power splitting (EPS). For the experiments, the EPS and RUPS networks were developed using lumped-element directional couplers. The fabricated RUPS Doherty PA, based on a 0.25- $\mu$ m GaN HEMT monolithic microwave integrated circuit (MMIC) process, achieves superior overall performance at 2.14 GHz compared to the conventional EPS Doherty PA, without requiring any additional circuitry. The results verify that the RUPS technique can enhance the performance of asymmetric Doherty PAs.

Keywords

• Doherty power amplifier (Doherty PA)
• input power splitting
• directional coupler
• gallium nitride (GaN)
• monolithic microwave integrated circuit (MMIC)
• long-term evolution (LTE)