Extension of High-Efficiency Range of Doherty Amplifier by Using Complex Combining Load

Abstract

In this paper, a novel Doherty power amplifier (DPA) configuration with a complex combining load (CCL) is presented to extend the high-efficiency range of the amplifier. Theoretical analysis of dynamic load span, current ratio, and drain efficiency reveals that CCL can offer a new degree of freedom to boost the output back-off (OBO) of the DPA. For verification, a 2-GHz equal-cell GaN HEMT-based DPA is simulated, prototyped, and measured with both complex and resistive combining loads (RCLs). Under continuous wave (CW) excitation, measurement results show that the proposed DPA can attain an OBO of 9.1 dB, which is 3.6 dB higher than that of the RCL design. In addition, by the use of single-carrier WCDMA signal with peak-to-average power ratio of 9.6 dB and at an average output power of 33.2 dBm, the proposed design is found to deliver an average drain efficiency of 57.4%. In the absence of multi-cell or enlarged auxiliary device, this approach offers a low-cost and simple DPA solution with extended OBO, as well as good Doherty behavior.Index Terms-Complex combining load (CCL), Doherty power amplifier (DPA), drain efficiency, load modulation, output back-off (OBO).

A novel design method for extending power back‐off range of broadband Doherty power amplifier

“…Based on the load modulation theory, the OBO of the DPA was expressed as where α is the power ratio of the peaking amplifier and the carrier amplifier at the saturation point, and β is the ratio of the output power of the main amplifier at the saturation point and the OBO point. Meanwhile, the parameter β is also the ratio of the optimum drain load at the OBO point and the saturation point . Therefore, the required OBO level can be determined by the appropriate selection of α and β values.…”

“…On the other hand, considering that the matching network is lossless and reciprocal, the scatter parameter matrix of the matching network can be given as follows: …”

“…However, with the application of high order modulation technologies, the 6 dB OBO can no longer meet the system requirements, and the design of the DPA with extended power back‐off range is an urgent problem to be solved. In addition, as the signal bandwidth is getting larger and larger, the design of broadband DPA is also one of the research hotspots …”

A Broadband High-Efficiency Doherty Power Amplifier With Integrated Compensating Reactance

“…The influence of complex impedance seen at the combining point on the back-off efficiency of the DPA at a specific frequency has been discussed in [23]. To analyze the effect of the reactance of the common load over a wide frequency range, assuming the common load Z L =R L +jX L and R L =0.5Z 0 , the normalized carrier load impedance Z C_low at low and high frequencies (0.75f 0 and 1.25f 0 ) as a function of the reactance of the common load (X L ) can be calculated according to (6) and the result is shown in Fig.…”

High Efficiency Power Amplifiers for Modern Mobile Communications: The Load-Modulation Approach

“…The main drawbacks of this solution are device under-utilization and increased bias circuit complexity. In [48] and [49], instead, a wide HEPR for a symmetric DPA is achieved by modifying the output power combiner, thus ensuring a high power utilization for both transistors, while in [50], electronically-tunable devices are adopted to dynamically adjust circuit parameters as a function of the average input power level, maintaining high efficiency even in deep OBO conditions. A novel technique for enhancing the HEPR of traditional symmetrical DPAs, based on adopting an output impedance for the Auxiliary stage different from an open circuit and changing the phase delay of the IIN, has been recently proposed in [51].…”