Frequency Response Analysis and Bandwidth Extension of the Doherty Amplifier
Frequency Response Analysis and Bandwidth Extension of the Doherty Amplifier
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DOI：
10.1109/tmtt.2010.2098040
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发表时间：
2011-04-01
影响因子：
4.3
通讯作者：
Boeck, Georg
中科院分区：
文献类型：
--
作者：
Bathich, Khaled;Markos, Asdesach Z.;Boeck, Georg
对Doherty放大器进行了完整的频率响应分析，给出了两条中心频率为1/4的四分之一波长传输线组成的常规输出合成网络的频率响应分析。推导了在整个动态范围和任意频率下的输出功率和效率的表达式。分析表明，效率提高的量以及最大输出功率都随着偏差的增大而减小。例如，推导出的公式表明，传统Doherty放大器的漏极效率Eta>；=52.7%，比B类放大器效率提高至少13.4%，分数带宽高达33.3%。文中还分析了一种改进的输出合成网络，该网络使用了阻抗变换比降低的Lambda/4线，使得Doherty放大器的带宽比传统设计有了很大的扩展。为了验证分析结果，设计了三个非对称GaN-Doherty功率放大器(DPA)，第一个DPA基于传统的输出合成网络，第二个DPA基于所提出的网络。测试结果表明，在5-6分贝退避时，第一个DPA的漏极效率为ETA&>52.7%，分数带宽(1.7-2.25 GHz)超过28%；而采用所提出的输出合并网络的DPA具有比第三个参考常规DPA更好的宽带性能，其退避漏极效率为Eta&>52.7%，分数带宽(1.7-2.6 GHz)超过42%。据作者所知，到目前为止，所设计的DPA具有最高的带宽。
A complete frequency response analysis of the Doherty amplifier is presented with the conventional output combining network consisting of two quarter-wavelength (lambda/4) transmission lines at a center frequency. Expressions for output power and efficiency were derived over the whole dynamic range and at any frequency. The analysis shows that the amount of efficiency enhancement, as well as the maximum output power, reduce as the deviation from increases. For instance, the derived expressions show that a conventional Doherty amplifier has a drain efficiency of eta >= 52.7%, which represents at least 13.4% efficiency enhancement over a class B amplifier, and up to 33.3% fractional bandwidth. A modified output combining network, using lambda/4 lines with reduced impedance transformation ratio, is also analyzed, which results in a bandwidth extension of the Doherty amplifier when compared to the conventional design. To verify the derived analyses, three unsymmetrical GaN Doherty power amplifiers (DPAs) were designed and characterized; the first DPA was based on the conventional output combining network, while the second DPA was based on the proposed network. Measurements showed that the first DPA had, at 5-6-dB back-off, a drain efficiency of eta >= 52.7% and over 28% fractional bandwidth (1.7-2.25 GHz), while the DPA with the proposed output combining network had a better wideband performance than the third reference conventional DPA, with a back-off drain efficiency of eta >= 52.7%, and over 42% fractional bandwidth (1.7-2.6 GHz). To the best of authors' knowledge, the designed DPAs have the highest bandwidths reported thus far.