July 9, 2020
Expand your knowledge of today’s Wi-Fi RF filter technology helping design engineers create state-of-the-art product designs for the world. In this blog, Tony Testa provides practical advice on bandBoost™, coexBoost™ and edgeBoost™ filter technologies and how they provide engineers the ability to mitigate interference and boost bandpass signal performance needed in our wireless world.
Filter technology used in gateways, cell phones and other wireless devices is critical to mitigating crosstalk interference, maintaining peak signal performance, and optimizing system efficiency. Without these filters, designers would struggle to meet many required system-level specifications that provide us ubiquitous, always-on connectivity in our homes, businesses and cities.
Early on, while working with our customers, Qorvo engineers saw a need to use filter technology to provide better overall system performance. We began helping our customers design filters into their design to achieve several important product specifications. These filters also helped make the product design engineer’s job easier by providing additional margin to ensure final product certification.
Qorvo provides three styles of filters. The individual filter styles are called bandBoost™, coexBoost™ and edgeBoost™ filters. The way they are used in a system differentiates them from each other.
coexBoost filters are used on both the receive and transmit side of an RF Path,
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targeting applications where signals near Wi-Fi need to operate simultaneously. These filters have steep band edge skirts. This is key in maintaining Wi-Fi signal quality and making certain coexistence is maintained with the Wi-Fi transmitter and receiver.
A good example of this is the Band 40 cellular signal and the 2.4 GHz Wi-Fi band. Band 40 operates from 2300 to 2400 MHz, while the Wi-Fi band 2.4 GHz operates from 2412 to 2484 MHz. This means that the high end of the Band 40 channel is only 12 MHz from the Wi-Fi 2.4 GHz band. Thus, steep filter skirts are required on both Band 40 and Wi-Fi filters. Wi-Fi coexBoost filters offer these steep skirts and reject the close proximity Band 40 signal from interfering with the Wi-Fi channel being transmitted and received.
The bandBoost filters provide band isolation between closely aligned signals. These filters improve Wi-Fi multi-user MIMO network capacity. They do this by helping multiple Wi-Fi networks support different users simultaneously – when these users are operating on separate channels in the same channel space. Thus, removing possible network interference.
Here’s an application example: In today’s tri-band Wi-Fi systems (2.4 GHz, 5.2 GHz + 5.6 GHz configurations), these bandBoost filters are used to improve system capacity. These three channels are sometimes used at the same time. Thus, these filters minimize the interference between each of these network signals and enable dividing the spectrum (U-NII 1-2a and UNII 2c-3) for both backhaul and client communications simultaneously.
The edgeBoost filters are added to the transmit side of the RFFE to increase signal performance. Mainly when a Wi-Fi signal is close to the edge of the Wi-Fi Channel band, such as channel 1.
For example, radios are not allowed to create “noise” outside their band, and on the channels close to the edge of the band. However, in cases when the signal is transmitting at full power, there may be a possibility of “bleed noise” outside the band, which is commonly resolved by reducing the output power in these channels. But this has implications on overall signal output and range. By using edgeBoost filters, the need to reduce the output power goes away. These filters reduce the bleeding of the radio signals outside of the band. Thus, the radio can transmit in these edge channels at maximum power and range.
Our primary go-to filter technology is the Bulk Acoustic Wave (or BAW). It’s best suited for 1 GHz or more. Because Wi-Fi is in the range of 2.4, 5 and soon to be 6 GHz, BAW technology works great for these frequency ranges.
BAW has superior insertion loss capabilities to help minimize RF path loss. The other advantages of BAW are its steep band edge skirts and thermal dissipative characteristics.
BAW filters are Solidly Mounted Resonator (SMR) structures and remove thermal heat much more efficiently than other filter technologies, such as Film Bulk Acoustic Resonator (FBAR). SMR BAW uses an acoustic reflector comprised of solid layers below the piezoelectric resonator. These solid layers provide a direct link to the silicon substrate below it, allowing the heat generated within the filter to efficiently move away from the piezo resonator through the reflector layers. Thus, any increase in system heat has minimal effect on SMR BAW filter and system performance, making it a good option in filter technology.
These coexBoost, bandBoost and edgeBoost filters can make such a difference in today’s Wi-Fi end-product design because they help system designers mitigate or entirely remove system-level challenges. Additionally, these filters can reduce design time, by creating viable go-to solutions for a Wi-Fi system designer both in the form of a highly integrated RFFE or simple plug-and-play discrete product.
Key architecture and quality-of-service (QOS) benefits from these filter solutions allow for optimal power usage across all useable spectrums. This allows for maximum use of channels at full power, providing users max range and solid connections. The savings aggregate all the way to the service providers, ensuring no “dead spots” and reducing service calls and truck rolls.
The key to creating any end product in a timely manner and with guaranteed end certification is to have all the tools needed at your fingertips. These filters offer that. By using coexBoost, bandBoost and edgeBoost filters in our highly integrated RFFE solutions, we help engineers reduce tedious, time-consuming design. For example, using a drop-in solution like the QPF7219 2.4 GHz iFEM provides all the RFFE capability – without the hassle of adding tuning and matching components and time typically required when using a discrete approach.
However, that being said – we also offer these BAW filters in discrete form – bandpass and multiplexer topologies (i.e., 885136, QPQ1903, QPQ1904, QPQ1907, QPQ2455, QPQ2456) for those Wi-Fi end-product designs that require more flexibility. These discrete filter solutions are also drop-in fixes to mitigating the above-discussed signal problems for all Wi-Fi end-products and have saved the day to bring regulatory requirements in line for many designs.
We have seen success with operators using these filters to mitigate interference and the ability to provide optimized signal range for best-in-class user experience. For operators, the user experience is one of the most important Key Performance Indicators (KPIs) they have. This is what keeps the user happy and allows operators to meet their customer needs. These filters are imperative to optimizing the user experience by allowing simultaneous receive and transmit ability even when in close proximity to other wireless signals. These filters also mitigate the interference inside a Smart Home when multiple users are doing different wireless related functions, such as talking on the phone, downloading a movie, adjusting your room temperature, operating a camera or talking with Alexa on your Echo Dot.
This improved Quality of Service (QoS) can reduce customer complaints, unnecessary truck-rolls as well as reduce the number of equipment (extender) issuance. Thus, keeping users connected at all times around their premise.
With all these wireless signals and standards in constant “on-mode” around us, there are bound to be some cross-over interferences that occur. But using these coexBoost, bandBoost and edgeBoost filters in your Wi-Fi end-product design, those issues essentially go away. These filters help designers provide products that function at peak performance while optimizing the user experience. The wireless signals around our homes, offices, cities, and airports are only growing in number. As technology continues to advance in the wireless ecosystem, more use cases will arise. This means we will need even more ways to mitigate or completely rid the possibility of cross-over interference as well as providing ways to increase signal range. These filters will help system designers create state-of-the-art products for Wi-Fi products well into the future.
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