Investigating and optimising linearity in load modulated balanced amplifier

功率放大器的频谱效率、线性度和功率效率是功率放大器设计中需要考虑的三个最重要的因素。通常，必须在这三个参数之间达成妥协，一方面是频谱效率和线性度，另一方面是功率效率。当试图以高功率输出操作PA时，必须牺牲原始信号的完整性。Doherty放大器是一种常用的PA架构，它提供了良好的功率效率，而不会使原始信号失真太多。Sheppard等人开发了一种宽带可重构功率放大器，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，这允许放大器的工作频率是动态的，从而允许更大的带宽。控制信号与输出RF信号重新组合，以便不影响PA的效率。这种技术允许在比标准Doherty PA更大的带宽下实现约50%的效率[2]。柯林斯等人以正交LMBA的形式进一步阐述了LMBA，该正交LMBA在控制信号中需要比标准LMBA更低的功率[3]。为了保持输出信号与输入信号的一致性，该参数至关重要。通过将控制信号施加到平衡放大器（如LMBA）中，可以提高线性度，同时保持LMBA的宽带功率效率。最初，可以将平衡Doherty放大器嵌入OLMBA中，取代平衡晶体管。通过仿真和原型设计，可以对这种设计进行表征，重点是捕获失真和线性度-尽管功率效率仍然是一个重要的标准。从这一点上，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。[1]D. Shepphard，J. Powell，S. Cripps，“An Efficient Broadband Reconfigurable Power Amplifier Using Active Load Modulation，”IEEE microwave and wireless components letters，2016年6月26日，第6期，第443-445页[2] R. Quagila，S. Cripps，“用于电信应用的负载调制平衡放大器”，IEEE微波理论与技术汇刊，第66卷，第3期，第110页。1328-1338，2018年3月[3] D.柯林斯河Quagila，J. Powell，S. Cripps，“正交LMBA：一种具有宽带可重新配置性的新型RFPA架构”，IEEE微波和无线组件快报，第30卷，第9期，pp. 888-891，2020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