[Guide]This article is the first in a series of blogs, introducing the challenges faced by Wi-Fi front-end design. The next part will discuss coexistence and interference issues. For wireless access points or customer premises equipment (CPE), it is difficult to fully consider thermal management and affected parameters before obtaining FCC certification. In order to avoid the need to change the design at the last moment due to interference, coexistence or the linearity of the radio frequency front end (RFFE), be sure to use the thermal parameters of the component to design. This blog post explains the biggest thermal challenge faced by Wi-Fi front-end design.
Improve smart home capabilities
Currently, each household has an average of 12 clients or Internet of Things (IoT) products communicating with each other, but this number will increase in the coming years. Intel believes that by 2020, the number of home clients will increase to 50; and Gartner predicts that by 2020, there will be 20.4 billion devices connected to the Internet.
In today’s wireless homes, communication operators and retailers usually provide a large wireless router that uses raw power to cover the entire home. However, with the rapid growth of household equipment and the rapid development of the Internet of Things, the single router model has become increasingly difficult to meet the needs of smart homes.
Therefore, new application models are constantly evolving. Consumers find that deploying more routers or nodes in their homes helps home routers/modems provide more client and data backhaul services. This new mesh network model ensures the wireless capabilities of the entire family through enterprise-level systems using technologies adopted in some office headquarters, hospitals, and university campuses.
Because of the application of this mesh network model and the integration of more standards and functions in the equipment, it is not surprising that the complexity of the radio frequency in the access point has increased.
The Internet of Things brings some challenges:
● The demand for wireless broadcasting has increased. Today’s access points not only integrate Wi-Fi functions, but also support Zigbee, Bluetooth, Bluetooth Low Energy (BLE), threading, and Narrowband Internet of Things (NB-IoT). Operators are also trying their best to cover households that have not been connected to the network before. LTE-M (machine-to-machine version of LTE) supported by operators is an example of entering some Wi-Fi gateways.
● The number of users in each household increases. There is no longer just one or two computers and a few phones in a family. Today, several computers, TVs, smart phones, wearable devices, secure networks, wireless devices, etc. must be connected to Wi-Fi and the Internet.
● Additional Wi-Fi frequency band. The device no longer has only one 2.4 GHz frequency band and one 5 GHz frequency band. Now, there are up to 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 in Wi-Fi access points or nodes.
● Reduce size and expand functions. Wi-Fi manufacturers are making Wi-Fi devices smaller, more stylish, more decorative, and less obtrusive. They also produce some devices that can adapt to various climates or add multiple functions, such as night light functions.
The following block diagram compares the old and new access points, highlighting the complexity of RFFE design today.
All these changes in the Wi-Fi front-end design have increased the number of RF chains and have become the culprit of the overall heat of the access point. The increase in device temperature also exacerbates the RF tuning problem, especially when the box size is the same or smaller.
In the Wi-Fi field, one of the most critical design challenges that engineers need to solve is product temperature. In today’s products, if left at a room temperature of 25°C, the average temperature of the parts will reach 60°C or higher. It is important to consider this issue in the early stages of the design to help minimize redesign or additional costs.
What challenges does heat pose to the function and coverage of the RF front-end
Temperature affects three RFFE components:
1. Power Amplifier
2. RF switch and low noise amplifier (LNA)
Let’s understand the thermal challenges of each category and Wi-Fi design considerations.
In the Wi-Fi field, one of the most critical design challenges that engineers need to solve is product temperature.
#1: How to solve the power amplifier?
Engineers often have to balance linearity, power output, and efficiency in each RF link. The use of optimized high linearity power amplifiers or front-end modules (FEM) can optimize system efficiency and reduce overall heat generation. At the same time, the problem of low system processing efficiency is also reduced.
RF engineers should also consider several Wi-Fi design trends that affect power amplifiers:
Use of Time Division Duplex (TDD). The use of TDD in Wi-Fi networks means that the power amplifier will pulse on and off during operation, that is, alternately transmitting and receiving function signals. This increases the transients of the power amplifier, leading to high temperatures.
Tighter Error Vector Magnitude (EVM) specifications. 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 a highly linear FEM to optimize the EVM, which ultimately helps reduce the overall temperature of the product.
Higher modulation scheme. In order to achieve higher capacity and data rate, Wi-Fi design is shifting from 256 QAM to 1024 QAM modulation scheme. After 1024 QAM is used for modulation, each symbol transmits 10 bits of data instead of 8 bits of data in 256 QAM. But as data rates increase, EVM on RFFE becomes the main focus. In 1024 QAM, the constellation points are very dense, and the processor must use complex system decoding to distinguish each point. When the processor is under high load, the heat of the device and equipment will increase.
The impact of RFFE performance on the overall current consumption of the system processor. Poor RF front-end performance means that the processor will have to work heavily to meet the requirements of the entire system. Increasing the load on the processor will also increase the heat of the system hardware.
#2: What about RF switches and low noise amplifiers (LNA)?
In the switch, the insertion loss also generates excessive heat. When the insertion loss increases and the signal strength decreases, the power amplifier will work at a high load to compensate and promote higher output, but this reduces the efficiency. The reduced efficiency means more heat in the equipment. The use of a high-linearity low-loss switch can ensure that the insertion loss in the entire frequency band is within the specification range.
Receive throughput is highly dependent on LNA gain and noise figure. Although LNA has no significant effect on heat generation, the heat on the LNA can severely affect throughput. Heat reduces the noise figure, and depending on the circuit design and wafer technology choice, compensation for this may lead designers to adopt specific solutions.
#3: Finally, the filter
The RF filter drifts to the left or right due to temperature changes, as shown in the SAW and BAW diagrams below. These shifts may cause high insertion loss at the edge of the frequency band, which in turn causes the gain of the RFFE or the POUT response to decrease. If the filter drifts too much (as shown in the SAW diagram), the power amplifier will drive more power output to compensate for the insertion loss. This increases current and reduces system efficiency.
Using a filter with high insertion loss can reduce linearity and increase the RF chain OUT. A major advantage of Qorvo’s LowDrift™ Bulk Acoustic Wave (BAW) filter is its stability in terms of temperature drift. The diplexer, bandpass filter and coexistence filter adopt BAW technology, which has low temperature drift, which helps to reduce insertion loss and achieve good product heat dissipation.
Read More Design Tips: Resolving Interference in a Crowded Wi-Fi Environment
Watch the detailed video “Chalk Talk” for more Qorvo Wi-Fi wireless connection solutions.
Design considerations for power consumption: Qorvo’s approach
Heat will degrade the performance of the entire system (such as throughput, range, and interference resolution). Therefore, it is very important to design the system by selecting RFFE components that can reduce heat. In the transmission chain, the focus should be on balancing link budget requirements, such as system linear power.
A As devices migrate from 802.11ac to 802.11ax capabilities, product manufacturers must focus on using more efficient components. Qorvo requires its design team to increase linear power without increasing power consumption and design higher throughput devices with the same power consumption as previous generations of products. For example, the upcoming QPF4528 is an 802.11ax 5 GHz FEM that can transmit linear power and achieve -47dB EVM, which is higher than the current QPF4538, which is an 802.11ac 5 GHz FEM that can achieve -43dB EVM and has a lower The maximum power consumption.
Another product that integrates all heat dissipation functions is Qorvo’s QPF7200, which is a fully integrated front-end module (iFEM) that can reduce weight and design complexity while reducing system heat generation. QPF7200 module:
● Contains an efficient 2 GHz power amplifier to reduce heat
● Integrated FCC band-edge LowDrift BAW filter, which can resist temperature changes and provides the option to remove the required number of RF chains
● Includes an LTE Wi-Fi coexistence filter, which can eliminate the interference effects of LTE devices (such as phones or modems) and avoid throughput degradation
The operating temperature should be considered before FCC certification
With so many radios and RF chains squeezed together, it is particularly important to cooperate with RF vendors, which can help you achieve both low power consumption and linear power budget at the same time.
Although many systems are designed and modeled at room temperature, ask yourself, if the operating temperature reaches 60-70°C (140-158°F), how can these devices continue to operate? Don’t wait until FCC certification to think about solving this problem.
Stay tuned for the next part of this blog post series, where we will discuss Wi-Fi design challenges and solutions related to wireless interference/coexistence.