通过Rached Hajji和Kim Tran，Qorvo.USA, Inc. & Larry Dunleavy and Laura Levesque,Modelithics, Inc.
The demand for Power Amplifiers (PAs) continues to grow with the increase in industrial and military applications of wireless and microwave technologies. Current PA designs must meet increasingly challenging performance goals in terms of efficiency, gain, linearity, power and bandwidth. The optimal design of the complete PA usually requires some compromise between several of these goals, and the ability to closely analyze the circuit under various conditions helps engineers make these design decisions. With sufficiently accurate nonlinear models, these trade-offs can be optimized in simulation prior to building any hardware. This is true for evaluation board (EVB) reference designs as well as final application circuits.
In fact, simulation-based PA design with non-linear models is the best path to meeting these complex design challenges. An alternative is to use measured load-pull data to determine matching condition trade-offs for PA design. However, load-pull characterization is time-consuming, requires specialized equipment, is not always available to designers, and its use is limited to the specific biases, frequencies and impedance ranges used to take the data.
进入紧凑型非线性晶体管型号大大简化了PA设计，并启用外推的负载拉和其他非线性模拟，可以延伸到用于拍摄用于构建模型的数据的台阶条件。通过在电子设计阶段在输入和输出匹配网络中使用的寄生分析和特定特性，可以进一步增加模拟到测量的协议。在这项工作中，描述了一个160W GAN类AB功率放大器EVB示例，其设计仅基于Keysight Technologies先进设计系统（广告）的基于仿真的设计优化，具有先进的模型。以下摘要将说明设计过程，并显示如何使用仿真进行成功的第一通道设计，即使是具有具有挑战性的性能目标的原型。
功率放大器设计示例概述
The design example to be presented is a power amplifier EVB prototype that can deliver 52dBm (160W) P3dB minimum with at least 50% power added efficiency (PAE) over the frequency band 1.35 GHz to 1.75 GHz. The selected transistor device is Qorvo’s TGF2819-FS packaged GaN on SiC HEMT RF transistor. The device is based on Qorvo’s GaN25HV technology and features an operating frequency range of DC to 4 GHz and rated output P3dB power of 54dBm. A non-linear model for this device is contained within the Modelithics-Qorvo GaN Library, described elsewhere1,2.
The described EVB development relies solely on simulation-based design using Modelithics’ non-linear model for the Qorvo TGF2819-FS device, a temperature and bias-dependent non-linear model validated with single tone power and load-pull at 2 GHz and 3 GHz. So, there is no load-pull data available in the desired design band, but the model was validated for broadband S-parameter fitting over 0.1 to 8 GHz. The GaN HEMT non-linear model features and performance plots are detailed in a model data sheet (Figure 1）。对于设计者便利和参考，所有模型数据表都可用于所有博客主动和被动模型。EVB的非线性模拟和优化使用Keysight广告中的谐波平衡分析进行，并使用Montionum电磁（EM）共模进行了优化了匹配的网络，其与ModelICS可扩展的微波全球模型™进行了优化。
Design: Determine Source and Load Impedances
PA设计的第一步通常是在操作频带上确定目标源阻抗。在封装参考平面上完成了分立GaN HEMT模型的小信号仿真和源引导。使用理想匹配网络元件的小信号源阻抗匹配设计之后是HB仿真，然后是集总/分布式输入匹配网络的EM共模，如图所示Figure 2.
Next, the optimum load impedances were determined using a large signal load-pull simulation across the operating band, optimized for both max power and max efficiency.
The load impedance chosen to design the output matching network required some compromise between the maximum power and maximum efficiency simulated impedances. The resulting output matching network was evaluated with EM co-simulation and Modelithics capacitor and inductor models, and was compared to the target impedances selected from non-linear transistor model load pull simulation, as the plot ofFigure 3shows.
Further analysis of the output matching network design was performed to check the 2ndharmonic impact on power and efficiency across the operating band. This is to verify that the PA performance is not degraded inadvertently by a poor second harmonic condition, and is particularly important when the power discrete device does not have output pre-match inside the package (seeFigure 4）。
Build and Validate PA Evaluation Board
The power amplifier design was finalized and fabricated based completely on the predicted performance of the simulations using the non-linear GaN HEMT model and the parasitic capacitor and inductor models. The assembled prototype EVB and complete simulation schematic are shown inFigure 5.
的测量性能EVB原型excellent overall model-to-measurement agreement in essentially every aspect across the full PA operating frequency band. The wideband small signal predicted performance of the simulation aligned very well with the measurement, including the prediction of response in the second harmonic frequency band (Figure 6）。The large signal harmonic balance power sweep simulations showed accurate prediction, exceeding minimum design goals throughout the PA band, with more than 70% PAE, >52 dBm P3dB, and 3dB gain (G3dB) of 14-15dB (Figures 7and8）。概述了PA设计目标，仿真和测量的摘要Table 1.
Summary
A 160W GaN PA evaluation board example illustrates the excellent results that are possible using a simulation-based design flow with high accuracy models. The use of non-linear models, such as those in the Modelithics-Qorvo GaN Library, enables broad-band complex and multi-harmonic predictions and design optimizations. Design cycles for new EVBs and application-specific PA circuits are reduced significantly by eliminating the need for custom device characterization in cases where available load-pull data does not cover design application space. Design time is also reduced by enabling first pass design success so that extensive bench tuning is not required, or is minimized. This use of advanced scalable parasitic simulation models and EM co-simulation for matching and bias elements is also an important aspect of implementing efficient and successful PA design flows.
Acknowledgements and Additional Information
The simulation-based design process and results were presented as part of an exhibitor workshop presented by Modelithics, Inc., Qorvo USA and Keysight Technologies at the IMS 2017 conference held in Honolulu, HI in June 2017. The authors would like to thank Jack Sifri of Keysight Technologies for collaboration related to this work and his review of the manuscript.
可免费访问Modelithics®QorvoGaN库，可供批准的设计师使用，可以在：https://www.modelithics.com/mvp/qorvo。对于方便设计，可以在库安装中包含广泛的文档和与思想Qorvo GaN设备模型相关的工作空间。
References
1L. Dunleavy, H. Morales, C. Suckling and Kim Tran, “Device and PA Circuit Level Validations of a High Power GaN Model Library,” Microwave Journal, August 2016.
2L. Dunleavy，J. Liu，M. Calvo，H. Morales，L. Levesque和R. Santhakumar，高频GAN设备的先进的非线性和噪声模型，2017年11月微针和RF。
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