Analytical Modeling of the Dual-Input Digital Doherty Power Amplifier for Efficiency and Linearity Optimization

The paper presents a comprehensive theoretical analysis of dual-input digital Doherty power amplifiers (DPAs) and outlines a specific design methodology. The theory explains how adaptive input signals affect the linearity and efficiency of the amplifiers, as well as the necessary adjustments to the operating point of the peaking amplifier. Using the analytical model, the paper offers guidance on adjusting the input signal to achieve the highest efficiency, ensuring that the carrier amplifier remains in saturation mode within the load-modulated region. It also discusses the maximum theoretically achievable efficiency for digital DPAs, which serves as a benchmark for comparing results with other amplifier topologies. Additionally, the paper proposes a practical approach for implementing the adaptive input algorithm during the measurement of modulated test signals. This method combines the measured response of the DPA with the theoretically derived optimal input signal splitting pattern, creating test signals for both the carrier and peaking input paths of the DPA. This effectively addresses unseen sources of nonlinearity by the theoretical model within the input signal bandwidth. Validation experiments were conducted on a 50W dual-input DPA designed for 5G wireless communication at 3.5 GHz, utilizing a 90 MHz modulated signal.