Analysis, Design Optimization and Performance Comparison of Bias Adapted and Asymmetrical Doherty Power Amplifiers

Abstract

Doherty type Power Amplifier (DPA) design is one of the most practical efficiency enhancement methods that provide moderate linearity. Asymmetrical device usage and employment of bias adaptation are among the most commonly used Doherty architectures in recent applications. In this paper, the efficiency performances of bias adapted DPA and asymmetrical DPA are compared based on the efficiency expression that is derived in terms of the conduction angle. The efficiency of bias adapted DPA is analyzed in terms of conduction angle of the peaking device; various bias waveforms are proposed and their effects on enhanced efficiency performance are demonstrated. This paper also facilitates an approach to determine the required relative periphery of the peaking amplifier in order to have a fully load modulated asymmetrical DPA. Both DPA structures are designed and implemented at the output power of 50 dBm with nearly 60% drain efficiencies in 6 dB load modulation region. The measurements verify the better efficiency characteristics of the bias adapted DPA and asymmetric DPA in comparison to the conventional DPA. For the first time in the literature, as a fair comparison, the performances of asymmetrical DPA and bias adapted DPA are compared on the same platform and their advantages as well as drawbacks are demonstrated using measurement results.

Design of Asymmetrical Doherty Power Amplifier With Reduced Memory Effects and Enhanced Back-Off Efficiency

“…Research efforts on DPA have been mainly made to enhance the efficiency, improve the linearity and extend the bandwidth of the DPA. To overcome the efficiency degradation due to incomplete load modulation, solutions such as uneven power drive [1], gate bias adoption [2], asymmetrical structure [3] and modified load modulation network [4] were proposed. In addition, harmonic tuning [5], knee voltage effect mitigation [6] and digital DPA [7] were devised to further enhance the back-off efficiency.…”