Investigating and optimising linearity in load modulated balanced amplifier

在功率放大器（PA）的设计中，三个最重要的考虑因素是频谱效率、线性度和功率效率。通常，必须在这三个参数之间达成妥协，一边是频谱效率和线性，另一边是功率效率。当试图操作具有高功率输出的放大器时，必须牺牲原始信号的完整性。多尔蒂放大器是一种常用的PA架构，它提供了良好的功率效率，而不会过多地扭曲原始信号。然而，这种架构缺乏可调性，因此缺乏大型宽带应用。Sheppard等人开发了一种宽带可重构放大器，称为负载调制平衡放大器（LMBA）[1]。该器件利用隔离端口上的控制信号来调制器件的匹配，该器件允许放大器的动态操作频率，从而允许更大的带宽。控制信号与输出射频信号重新组合，以免影响扩音器的效率。该技术的效率约为50%，带宽大于标准Doherty PAs[2]。Collins等人以正交LMBA的形式进一步阐述了LMBA，它比标准LMBA[3]需要更低的控制信号功率。然而，这种装置缺乏的是线性。为了保持输出信号忠实于输入，这个参数是至关重要的。通过将控制信号应用于平衡放大器-与LMBA一样-希望线性度可以得到改善，同时保留LMBA的宽带功率效率。最初，平衡多尔蒂放大器可以嵌入到OLMBA，取代平衡晶体管。通过仿真和原型设计，可以对该设计进行表征，重点是捕获失真和线性-尽管功率效率仍将是一个重要的标准。由此，可以确定设计的优点和缺点，并可以探索新的架构，以最大限度地提高放大器的性能D. Shepphard， J. Powell， S. Cripps，“基于有源负载调制的高效宽带可重构功率放大器”，IEEE微波与无线元件快报，第26卷，第6期，第443-445页，2016年6月[3]R. Quagila， J. Powell， S. Cripps，“用于电信应用的负载调制平衡放大器”，IEEE微波理论与技术学报，第66卷，第3期，第1328-1338页，2018年3月[3]D. Collins， R. Quagila， J. Powell， S. Cripps，“正交LMBA：一种具有宽带可重构性的RFPA架构”，IEEE微波与无线元件学报，第30卷，第9期，第888-891页，2020年9月

Three of the most important factors to consider in the design of power amplifiers (PA) are the spectral efficient, linearity and power efficiency. Usually, a compromise must be struck between these three parameters, with spectral efficiency and linearity on one side and power efficiency on the other. When trying to operate PAs with high power output, the integrity of the original signal must be sacrificed. The Doherty amplifier is a commonly used PA architecture which provides good power efficiency without distorting the original signal too much. However, this architecture lacks tuneability and thus lacks large broadband application.Sheppard et al. have developed a broadband reconfigurable PA known as the Load Modulated Balanced Amplifier (LMBA) [1]. This device utilises a control signal on an isolated port in order to modulate the matching of the device which allows the amplifier's frequency of operation of be dynamic thus allowing greater bandwidth. The control signal is recombined with the output RF signal so as to not impact the efficiency of the PA. This technique allows for efficiencies of around 50% with greater bandwidth than standard Doherty PAs [2]. The LMBA has been further elaborated upon Collins et al. in the form of the Orthogonal LMBA which required lower power in the control signal than the standard LMBA [3].Where this device lacks, however, is linearity. This parameter is crucial in order to keep the output signal faithful to the input. By applying a control signal into a balanced amplifier - as with the LMBA - it is hoped that linearity can be improved upon while conserving the LMBA's wideband power efficiency.Initially, balanced Doherty amplifiers can be embedded into the OLMBA, replacing the balanced transistors. Through simulation and prototyping this design can be characterised, with a focus on capturing distortion and linearity - although power efficiency will remain an important criterion. From this, the benefits and drawbacks of thedesign can be identified and new architectures can be explored to maximise the performance of the amplifier.[1] D. Shepphard, J. Powell, S. Cripps, "An Efficient Broadband Reconfigurable Power Amplifier Using Active Load Modulation," IEEE microwave and wireless components letters, Vol 26, Issue 6, pp 443-445, Jun 2016[2] R. Quagila, S. Cripps, "A Load Modulated Balanced Amplifier for Telecom Applications", IEEE transactions on microwave theory and techniques, vol. 66, issue 3, pp. 1328-1338, Mar 2018[3] D. Collins, R. Quagila, J. Powell, S. Cripps, "The Orthogonal LMBA: A Novel RFPA Architecture With Broadband Reconfigurability", IEEE microwave and wireless components letters, vol. 30, issue 9, pp. 888-891, Sep 2020