Investigating and optimising linearity in load modulated balanced amplifier

在功率放大器(PA)的设计中，需要考虑的三个最重要因素是频谱效率、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功率放大器时，必须牺牲原始信号的完整性。Doherty放大器是一种常用的功率放大器结构，它在不太大失真原始信号的情况下提供了良好的功率效率。然而，这种架构缺乏可调性，因此缺乏大规模的宽带应用。开发了一种宽带可重构功放，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，从而允许放大器的工作频率是动态的，从而允许更大的带宽。控制信号与输出的RF信号重新组合，从而不影响功放的效率。与标准Doherty PAS[2]相比，该技术可以在带宽更大的情况下实现约50%的效率。LMBA对Collins等人作了进一步的阐述。以正交LMBA的形式，其控制信号中所需的功率比标准LMBA[3]更低。然而，这种器件缺少的是线性度。为了使输出信号与输入信号保持一致，该参数至关重要。与LMBA一样，通过在平衡放大器中应用控制信号，希望在保持LMBA宽带功率效率的同时改善线性度。最初，平衡Doherty放大器可以嵌入到OLMBA中，取代平衡晶体管。通过模拟和原型设计，可以确定这种设计的特点，重点是捕捉失真和线性度--尽管功率效率仍将是一个重要的标准。[1]D.Sepphard，J.Powell，S.Cripps，《使用有源负载调制的高效宽带可重构功率放大器》，IEEE微波和无线组件通讯，第26卷，第6期，第443-445页，2016年6月[2]R.Quagila，S.Cripps，《用于电信应用的负载调制平衡放大器》，IEEE微波理论与技术会刊，第66卷，第3期，第1328-1338页，2018年3月[3]D.Collins，[2]R.Quagila，S.Cripps，《用于电信应用的负载调制平衡放大器》，IEEE微波理论与技术学报，第66卷，第3期，第1328-1338页，2018年3月[3]D.Collins，[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，《The Orthogonal LMBA：A new RFPA Architecture with Broadband Refigurations》，IEEE微波和无线组件通讯，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