For wireless access points or client devices (CPEs), it is difficult to fully consider the parameters of thermal management and its effects prior to FCC certification. In order to avoid the trouble of last-minute changes caused by the coexistence or linearity of the radio frequency front end (RFFE) due to interference, it is necessary to design using the thermal parameters of the components. This blog post explains the biggest challenge facing Wi-Fi front-end design - heat.
Improve the load of smart homesThe current family has an average of 12 client or Internet of Things (IoT) products communicating with each other, but these numbers will increase in the next few years. Intel believes that by 2020, the number of home users will increase to 50, and Gartner predicts that by 2020, there will be 20.4 billion users worldwide using the Internet.
In today's wireless homes, communications carriers and retailers typically offer a large wireless router that uses raw power to achieve coverage across the home. But with the rapid growth of home devices and the Internet of Things, smart homes are pushing the capabilities of single-router mode.
As a result, new application models are evolving. Consumers have found that placing more routers or nodes at home helps provide more client and data backhaul services for home routers/modems. This new mesh network model uses enterprise-level systems to ensure the wireless capabilities of the entire home using technologies already in office headquarters, hospitals, and university campuses.
Undoubtedly, due to the mesh network model and the integration of more standards and functions, the RF complexity within the access point increases.
The Internet of Things brings several challenges:
The demand for wireless broadcasting has increased. Today's access points include not only Wi-Fi, but also Zigbee, Bluetooth, Bluetooth Low Energy (BLE), Thread and Narrowband Internet of Things (NB-IoT). Operators are also trying to find families that were previously inaccessible. Operator-supported LTE-M (machine-to-machine version of LTE) is an example of access to some Wi-Fi gateways.
There are more users in each family. The home no longer has only one or two computers and a few phones. Today, several computers, TVs, smartphones, wearables, secure networks, wireless devices, etc. are all connected to Wi-Fi and the Internet.
Additional Wi-Fi band. The unit no longer has a 2.4 GHz band and a 5 GHz band. There are now eight independent 2.4 GHz and eight 5 GHz paths. This change allows us to have MIMO (Multiple Input/Multiple Output) and Multi-User MIMO (MU-MIMO) paths within Wi-Fi access points or nodes.
Reduce size and expand functionality. Wi-Fi manufacturers are making Wi-Fi devices smaller, more stylish, more decorative, and less prominent. They also make parts around the clock or add versatility, such as luminous power.
All of these changes in the Wi-Fi front-end design increase the number of RF chains and contribute to the overall heat within the access point. This increase in unit temperature also increases the RF tuning challenge, especially when the boxes are the same size or smaller.
In the Wi-Fi world, one of the most critical design challenges engineers need to address is product temperature. In today's products, the average temperature of the components is 60 ° C or higher, and at room temperature of 25 ° C. It is important to consider this fact early in the design to help minimize redesign issues or additional costs.
How does heat challenge the capabilities and range of RF front ends?
Temperature affects three RFFE components:
Power amplifier
RF Switch and Low Noise Amplifier (LNA)
filter
Let's take a look at each category of thermal challenges and Wi-Fi design considerations.
In the Wi-Fi world, one of the most critical design challenges engineers need to address is product temperature.
#1: What is the power amplifier factor?Engineers often balance the linearity, power output, and efficiency of each RF link. Optimize system efficiency and reduce overall heat generation with an optimized high linear power amplifier or front end module (FEM). This also solves the problem of inefficient processing.
RF engineers should also consider several Wi-Fi design trends that affect power amplifiers:
Use Time Division Duplex (TDD). Wi-Fi networks use TDD, which means that the power amplifier is pulsed on and off during operation - alternate transmission and reception functions. This increases the PA transient, which is the cause of the high temperature.
A more difficult error vector magnitude (EVM) specification. EVM is a measure of modulation quality and error performance. In 802.11ac, the EVM specification is -35dB, but in Wi-Fi's next standard 802.11ax, the specification is increased to -47dB, which is more difficult for Wi-Fi component designers to meet. Design engineers must design highly linear FEMs to optimize the EVM and ultimately help reduce the overall temperature of the product.
A higher modulation scheme. To achieve higher capacity and data rates, the Wi-Fi design is moving from 256 QAM to 1024 QAM modulation. With 1024 QAM modulation, there are more bits per signal - 10 bits per signal, and only 8 bits in 256 QAM. However, as data rates increase, EVM on RFFE becomes a major concern. In 1024 QAM the constellation is very dense and the processor must use complex system decoding to distinguish each point. When the processor is more difficult to work, the heat of the unit device increases.
How RFFE performance affects the overall current consumption of the system processor. Poor RF front-end performance means that the processor will have to work harder to meet the requirements of the entire system. Using a processor increases the heat of the system hardware.
In the switch, the insertion loss also generates excessive heat. As the insertion loss increases and the signal strength decreases, the power amplifier is more difficult to compensate and push for higher output, which reduces efficiency. The lower the efficiency, the more heat the device has. Using high linearity, low loss switches ensure insertion loss across the entire frequency range.
Receive throughput is highly dependent on LNA gain and noise figure. Although the LNA does not contribute significantly to heat generation, the effects of heat on the LNA can severely impact throughput. Heat reduces the noise figure and, depending on the choice of circuit design and wafer technology, compensation for this allows the designer to get a specific solution.
#3: Finally, the filterThe RF filter drifts to the left or right due to temperature changes, as shown in the SAW and BAW diagrams below. These shifts can result in high insertion loss at the edges, which can result in low gain or P OUT response of the RFFE. If the filter drifts too much (as shown in the SAW diagram), the PA will push more power output to compensate for the insertion loss. This increases current and reduces system efficiency.
Using a high insertion loss filter reduces linearity and increases the RF link P OUT . Qorvo LowDrift? A major advantage of bulk acoustic wave (BAW) filters is their stability in temperature drift. The duplexer, bandpass filter and coexistence filter use BAW technology with low temperature drift to help reduce insertion loss and result in good product heat dissipation.
Power design considerations: Qorvo's approach
Heat reduces overall system performance (such as throughput, range, and interference resolution). Therefore, it is important to design a system by selecting a heat-reducing RFFE component. In the transmission chain, the focus should be on balancing link budget requirements, such as system linear power.
As devices migrate from 802.11ac to 802.11ax, product manufacturers must focus on using more efficient components. Qorvo challenges its design team to increase linear power without increasing power consumption - designing higher throughput devices with the same power consumption as previous generations. For example, the upcoming QPF4528 is an 802.11ax 5 GHz FEM that delivers linear power with -47 dB EVM - higher than the current QPF4538 FEM, 802.11ac 5 GHz FEM, achieving -43 dB EVM with lower Maximum power consumption.
Qorvo's QPF7200 is a fully integrated front-end module (iFEM) that reduces weight and design complexity while reducing system heat. QPF7200 module:
Includes an efficient 2 GHz power amplifier to reduce heat
Integrated FCC rib LowDrift BAW filter to withstand temperature changes and provide the option to remove the required number of RF chains
Includes an LTE Wi-Fi coexistence filter that eliminates the effects of interference from LTE devices such as phones or modems, reducing throughput
Consider the operating temperature before FCC certification
With so many radio and RF chains, it's important to work together with RF vendors to help you achieve both low power and linear power budgets.
Although many systems are designed and modeled at room temperature, ask yourself how to operate at 60-70 ° C (140-158 ° F) while the equipment is running. Don't wait until the FCC certification to find out.
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