How Not to Run Hot: Overcoming Thermal Challenges in Wi-Fi Front-End Designs (Part 1)
2017年11月14日
这是第一个查看Wi-Fi前端设计的设计挑战中的第一部分。第2部分检查共存和干扰。
用于无线接入点或customer premises equipment (CPE)，它可能很难完全考虑热管理和在FCC认证之前受其影响的参数。为了保护自己由于干扰，共存或射频前端（RFFE）线性而导致的最后一刻更改的头痛，请务必在记住中使用组件热参数设计。该博客帖子介绍了Wi-Fi前端设计面临的最大热挑战。
增加智能家庭的能力
平均而言，今天的家庭有12个客户或物联网(IoT)products communicating with each other, but these numbers will increase in coming years.Intel相信househo的数量ld clients will increase to 50 in 2020, whileGartner2020年将在全球范围内使用204亿连接的东西。
在当今的无线家庭中，通信运营商和零售商通常提供了一个大型无线路由器，使用原始电源来实现整个房屋的覆盖范围。但随着家庭设备和物联网的急剧增加，智能家庭正在推动单路由器模型的功能。
As a result, new application models are evolving. Consumers are finding that placing more routers, or nodes, in the home helps service more clients and data backhaul to the home router/modem. Thismesh (or distributed Wi-Fi) network modelensures wireless capability across a home using some techniques that are already present in office headquarters, hospitals and college campuses via enterprise-level systems.
相关博客文章：分布式Wi-Fi如何支持连接的智能房屋
The IoT challenge
It’s no surprise that the RF complexity within the access point increases because of this mesh networking model and as devices integrate more standards and capabilities.
物联网带来了几个挑战：
- 添加无线电需求。Access points today incorporate more than just Wi-Fi — they also supportZigbee,Bluetooth,蓝牙低能量（BLE）和线。Operators are also finding ways to reach households who previously didn’t have access. Operator-supportedLTE-M(the machine-to-machine version of LTE) is one example finding its way into some Wi-Fi gateways.
- More users within each home.房屋不再只有一两台电脑和一些手机。如今，几台计算机，电视，智能手机，可穿戴设备，安全网络，无线设备以及更全面连接到Wi-Fi和Internet。
- Additional Wi-Fi bands.单位不再有一个2.4 GHz频段和一个5 GHz频段。现在有高达八个个人2.4 GHz和八个5 GHz路径。这种变化给了我们MIMO(multiple input / multiple output) and多用户MIMO（MU-MIMO）paths within the Wi-Fi access point or node.
- Shrinking size and expanded functionality.无线上网manufacturers are making Wi-Fi units smaller, sleeker, more decorative and less obtrusive. They’re also making some units all-weather or adding multifunctionality such as night-light capability.
Block diagrams of older vs. new access points highlight just how complex the RFFE design is now.
Running hot
All these changes in the Wi-Fi front-end design increase the number of RF chains, contributing to the overall heat within the access point. This increase in unit temperature also increases the RF tuning challenges, especially when the size of the box is the same or even smaller.
在Wi-Fi的世界中，最关键的设计挑战之一工程师需要解决的是产品温度。在当今的产品中，组件受60°C或更大的平均温度，同时坐在25°C的室温环境中。重要的是要在设计中提早考虑这一事实，以帮助最大限度地减少重新设计的问题或额外费用。
RF前端如何提供高温挑战，以提供容量和范围
Temperature affects three RFFE components:
- Power amplifiers
- RF switches and low noise amplifiers (LNAs)
- 过滤器
让我们来检查每个类别的热挑战和Wi-Fi设计考虑因素。
在Wi-Fi世界中，最关键的设计挑战之一工程师需要解决产品温度。
#1: How does the power amplifier factor in?
Engineers often balance between linearity, power output and efficiency in each of the RF chains. Using optimized, highly linear power amplifiers or front-end modules (FEMs) optimizes system efficiencies, creating less overall heat. It also reduces processing inefficiencies.
RF工程师还应考虑几种影响功率放大器的Wi-Fi设计趋势：
- Use of time division duplexing (TDD).Wi-Fi网络使用TDD，这意味着在操作交替发送和接收功能期间PAS脉冲开启和关闭。这增加了PA瞬态，属于高温。
- More difficult error vector magnitude (EVM) specifications.EVM是一种调制质量和错误性能的衡量标准。在802.11ac中，EVM规范为-35 dB，但在Wi-Fi，802.11ax的下一个标准，this specification increases to -47 dB — which is more difficult for Wi-Fi component designers to meet. Design engineers must design highly linear FEMs to optimize for EVM, which ultimately helps reduce overall product temperature.
- Higher modulation schemes.帮助实现更高的容量和数据速率,Wi-Fi designs are moving from 256 QAM to 1024 QAM modulation schemes. With 1024 QAM modulation, there are more bits per symbol — 10 bits per symbol versus 8 bits in 256 QAM. However, as the data rate increases, EVM on the RFFE becomes a principal concern. The constellation is so dense in 1024 QAM that the processor must use sophisticated system decoding to distinguish each point. When the processor works harder, the unit device heat increases.
- How the RFFE performance affects the overall current draw on the system processor.Poor RF front-end performance means the processor will have to work harder to meet overall system requirements. Working the processor more increases system hardware heat.
＃2：RF开关和低噪声放大器（LNA）呢？
在开关中，插入损耗也可以产生多余的热量。当插入损耗增加并且信号强度降低时，PA更易于补偿和推动更高的输出，这会降低效率。较少的效率意味着从装置中加热更多。使用高线性度，低损耗开关在整个频段上保持规格内的插入损耗。
接收吞吐量高度依赖于LNA增益和噪声数字。虽然LNA对发热没有显着贡献，但热量对LNA的影响可能会急剧影响产量。热量降低噪声系数，并取决于电路设计和晶圆技术的选择，对此的补偿可以引导设计者特定的解决方案。
＃3：最后，过滤器
由于温度的变化，RF滤波器漂移到左侧或右侧，如以下锯与BAW图所示。这些换档可能导致带边的高插入损耗，这可能导致低增益或p出去来自rffe的回应。如果过滤器漂移过多（如SAW图中所示），则PA推动更多功率输出以补偿插入损耗。这增加了电流并降低了系统效率。
Using filters with high insertion loss can decrease linearity and increase the RF chain P出去。一个大的优势Qorvo的Lowdrift™散装声波（BAW）filters is their stability over temperature shifts. Diplexers, bandpass filters and coexistence filters that use BAW technology with lower temperature drift help mitigate insertion loss, and lead to good product thermals.
Read More Design Tips:Resolving Interference in a Crowded Wi-Fi Environment Using BAW Filters
Watch thisdetailed "Chalk Talk" videoto learn more about Qorvo's Wi-Fi connectivity solutions (37:56).
Design considerations for power consumption: Qorvo’s approach
热量可以降低整体系统性能（例如吞吐量，范围和干扰分辨率）。因此，通过选择减轻热量的RFFE组件来设计系统是重要的。在传输链中，重点应在平衡链路预算需求，例如系统线性电源。
随着设备从802.11ac转移到802.11ax功能，产品制造商必须专注于使用更高效的组件。Qorvo向其设计团队提出挑战，要求他们在不增加功耗的情况下增加线性功耗，即设计与前几代产品功耗相同的更高吞吐量设备。一个例子是QPF4528，802.11Ax5 GHz FEM，传输实现-47 dB EVM的线性功率 - 高于电流QPF4538FEM，一个802.11ac 5 GHz FEM，实现-43 dB EVM，具有较低的功耗耗散。
Another product that integrates all the aspects of heat mitigation is Qorvo’sQPF7200.，一个完全集成的前端模块（IFEM），可降低重量和设计复杂性，同时也降低系统热量。QPF7200模块：
- 包含一个高效的2 GHz功率放大器，可减少热量
- Integrates an FCC bandedge LowDrift BAW filter, which is resistant to temperature shifts and provides the option to remove the number of required RF chains
- Includes an LTE Wi-Fi coexistence filter that negates the interference effects of LTE devices such as phones or modems, which could degrade throughput
Think about operating temperatures before FCC certification
With so many radios and RF chains squeezed together, it’s important to partner with an RF supplier that helps you achieve low power dissipation and linear power budgets simultaneously.
Although many systems are designed and modeled at room temperature, ask yourself how it will operate at 60-70°C (140-158°F) when the device is operating. Don’t wait until FCC certification time to find out.
查看第2部分在我们的系列中，我们解决了无线干扰/共存的Wi-Fi设计挑战，以及克服它们的智能提示。
Have another topic that you would like Qorvo experts to cover?Email your suggestions to theQorvo.博客team它可以在即将到来的帖子中得到特色。请在电子邮件正文中包含您的联系信息。
Wi-Fi 802.11ax：这一切是什么？
探索802.11AX的Wi-Fi连接的未来。
Read the White Paper >