RF/DSP Codesign Methodology of Enhanced Doherty Amplifiers

In this brief, a mixed radio frequency/digital signal processing (DSP) codesign approach is proposed to enhance the performance of Doherty power amplifiers (PAs). For the hardware optimization, a load-pull-based design methodology is proposed to determine the optimal matching elements of the main amplifier for enhanced efficiency at back-off. Subsequently, DSP control of the baseband input signal is used to efficiently distribute the drive power between the main and auxiliary amplifiers in order to enhance the efficiency at high power levels and also to improve the linearity. Precisely, the input power is evenly distributed between the two amplifiers at the back-off region and then unequally split with more drive into the auxiliary amplifier once the latter turns on. This allows for improving the load modulation behavior of the Doherty PA and flattening its gain response, which yield enhanced efficiency and improved linearity. For the experimental validation, the proposed codesign approach is applied to implement a dual-input Doherty PA based on a 10-W gallium nitride (GaN) device. Measurement results with wideband code division multiple access demonstrated improvements of up to 5% in average drain efficiency and up to 3 dB in adjacent channel leakage ratio.