The process of choosing RF front-end components for a Wi-Fi design is a challenging task given the stringent requirements and increased performance targets that need to be met for today’s consumers. There are many elements to consider, from cost and availability, to mitigating interference and thermal creep. While searching for the right part that meets all of your desired requirements can seem like an overwhelming task, dividing the process into more manageable steps can help narrow the options and provide for a more methodical approach.

As you move through the following phases, it should become apparent what parts will and won’t work given the parameters of your design. Before selecting any actual components, it’s important to coordinate with all teams involved in the product’s lifecycle to determine what kind of performance is required, account for known issues with procurement, and desired production timelines for hitting time-to-market goals. While it may be your responsibility as an engineer to determine the exact components to use, there are many varying interests to consider that will be directly impacted by the RF elements ultimately chosen.

Here are 3 design stages, that if followed in sequence, should provide a smoother process and result in selecting the best components for your next Wi-Fi design:

Initial Project Concept

In this first decision-making stage, members from product marketing, design leadership, and engineering teams come together to determine the nature of the final product, it’s target users and how the end device will eventually be positioned in the market. This conversation is critical for defining the product’s size, exact functionality and performance requirements, the operating environment in which it will be used, project budget, production timeline and planned resource allocation for accomplishing all of these goals. These decisions will help inform what components are used with respect to specific RF protocols needed, power consumption requirements, thermal conditions, interference considerations, testing standards and budgetary restrictions among other things. Besides defining the final product look, feel and cost, the project concept sets the foundation for the next two decision making stages.  

For example, when it comes to deciding on the environment in which your product concept will be used, there are many standards to consider that affect which kind of filters, PAs, LNAs and switches to use. In today’s complex, RF-rich homes and offices, multiple protocols operate simultaneously and choosing the ideal frequency for your design can vary greatly based on what the solution is meant to accomplish:

• Standards that operate at short- and mid-range coverage, such as Zigbee, Bluetooth, Thread and Z-Wave
• Standards that operate in longer ranges, like Wi-Fi, 3G/4G LTE and 5G

Regardless of which frequency is chosen, a big challenge is attaining seamless coexistence between all radios in a given environment. The standards outlined above operate in both licensed and unlicensed spectrums and are becoming more prevalent in Wi-Fi devices to support IoT expansion or offload large data streams. Knowing which protocols will need to be managed will go a long way in determining the necessary parts to add or remove from a final design.

By specifying the requirements for overall system functionality and design features early on in this project concept stage, marketing, engineering and sourcing teams can better visualize the end-product and work together toward the stated goals with clear direction and accountability. But knowing what’s desired from the end product and actually making it happen can be very different tasks.

Defining the System Architecture

During this design stage, all of the features and considerations outlined in the initial concept are reviewed by engineering to vet the feasability of elements such as product size, power needs, budget, thermal management, and throughput. Piecing these features together creates a more detailed picture to help effectively narrow down what type of components will be required to meet the desired product capabilities, and if there may be need to sacrifice any performance specifications based on what can actually be accomplished.

In order to further refine the project requirements, it’s also useful to ask questions such as:

• Is your solution going to use multiple-input/multiple output (MIMO)?
• Is it a Wi-Fi 5 (802.11ac) or Wi-Fi 6/6E (802.11ax) application?
• What capacity and speed will the environment demand?

While the data stream into a home, office or access point establishes the initial Internet bandwidth target, another factor which should be considered is network speed. Things that can affect the network speed may be:

• Distance between the client and the access point
• Interference from other clients on the same frequency
• Inherent Wi-Fi overhead for acknowledgements, transmission, and clear channel assessments

Interference is also a highly important factor to consider in guiding your choice of components. Coexistence between devices and within a device, including between wireless carrier signals or wireless standards, is both necessary for regulatory compliance, as well as proper device functionality. Common interference scenarios between Bluetooth, cellular bands and Wi-Fi can be planned for relatively easily, but it’s important to include other, less likely scenarios too, as many of today’s RF systems’ multiple antenna signals can interfere with each other. As a result, the coupling between affected antennas can be compromised leading to poor signal-to-noise ratios, receiver desense and dropped or interrupted wireless connections.

With all of these challenges in mind, begin narrowing the field of known requirements and communicate any issues around desired performance specifications that may not be feasable. The earlier these concerns are addressed, the better, so as not to waste precious time and money on redesigns further down the road. After compiling a list of specific performance metrics and proposed design solutions, start working with your procurement teams to research the best sources for supplying the needed parts within your desired timeframe and be sure to include plenty of lead time for testing and verifying all solutions once your design has been built.

Component Down-Selection

After moving through the two phases above, it’s time to start selecting specific components to test and use in your design. RF component selection is always a balancing act between thermal management, interference mitigation, cost considerations, quality, reliability, performance and size requirements. Using the information gathered from your initial design concept meeting and vetting process of your system architecture specifications, start selecting the specific parts needed for your final solution and work closely with your procurement team to purchase samples for initial solution build outs.

In choosing your final parts, keep in mind how each element may affect the whole system and any external considerations defined in previous design stages. For example, the RF PA efficiency and linearity will influence PCB thermals and overall package design, so managing the PA efficiency specifications under various Wi-Fi modes is important. PA efficiency is critical to avoiding costly re-designs, heatsinks or regulatory requirement failure. Care should therefore be taken when choosing the RF component with the efficiency needed for your solution. Be sure to maintain awareness as to how the component’s characteristics affect the end product’s size, range and performance.

When deciding on a final solution, integration is another important consideration. Designing with integrated solutions can reduce design time and tuning. Many highly integrated components also incorporate filter technology to mitigate interference, support coexistence and reduce thermal issues without compromising harmonic compliance and emissions. With integrated filters, your design team can spend less time tuning for discrete components and remove extra elements such as MLCCs – a smart option to reduce the size of your final product and overall BOM all the while achieving reliable coverage across the full allocated spectrum.

Although there’s a lot involved in deciding on final components for your next Wi-Fi design, we hope that following the steps outlined above will help provide a more refined approach for cross-functional decision making that supports the goals of all teams involved and results in a successful new wireless device.