The field of wireless communications is rife with complex mathematics, algorithms, and constraints. Still, the field continues to churn out newer, better protocols time and again. While protocols are generally designed from an algorithmic level, they still require hardware to make them work.
Different wireless protocols all operate differently, necessitating unique RF designs. Image used courtesy of Bonaiuto et al. and ResearchGate
In RF design, the front end is one of the most important hardware blocks. New wireless protocols, like Wi-Fi 6E, require updated front end design to support the protocol’s requirements, including bandwidth and power.
In this article, we’ll take a look at RF front-end design and ways that new protocols push their limits.
What Makes Up an RF Front End?
An RF front end is the part of the RF signal chain that is responsible for interfacing the antennas with the digital circuitry. While there are many different architectures and topologies, a general superheterodyne RF receiver front-end architecture consists of the antenna, impedance matching networks, a bandpass filter, an amplifier, and a mixer.
The front end of an RF receiver is highlighted in red. Image from Wikimedia Commons
The filter component of the RF front end is a straightforward concept, serving to filter out any signal or noise outside of the desired band. The amplifier design used in RF front ends is generally a low-noise amplifier (LNA). This device amplifies the signal to achieve the desired sensitivity while introducing as little noise to the signal as possible and maintaining a high level of linearity.
Mixers work with the local oscillator to lower the signal frequency. Image used courtesy of Marki Microwave
Finally, the mixer works with the local oscillator to convert the RF signal into an intermediate frequency (IF) signal. The IF signal is often significantly lower frequency than the RF signal. Lowering the frequency is useful for many reasons since circuit design at lower frequencies reduces complexity, including making demodulation simpler.
In addition, RF designs at the same IF can utilize the same circuitry, making it easier to design for many applications as opposed to the varying front-end requirements.
How New Protocols Influence Front-End Design
With this background in place, we can see why different protocols need different front-end designs. The important thing to understand about RF front-end design is that every piece of circuitry is meticulously optimized for a specific frequency to meet protocol-specific requirements; different wireless protocols require different frequency bands, bandwidths, sensitivities, and power.
Wi-Fi 6 vs. Wi-Fi 6E design protocols. Image used courtesy of NokiaMob
Changing the frequency of the protocol will require a new BPF, revised LNA and mixer designs, and new impedance-matching networks. Changing bandwidths, power, and sensitivity will also influence noise in the circuit and the power consumption of the front end.
An Example of a Wi-Fi6E Front-End Module
Wi-Fi 6E and its associated front-end modules is a relevant example of how an upgrade of the Wi-Fi protocol to the 6GHz band will require completely new front-end designs compared to Wi-Fi 6. For instance, Skyworks recently released two new front-end modules, SKY85784-11 and SKY85780-11, for wireless video streaming and indoor/outdoor network via Wi-Fi6E.
Block diagram of the SKY85784-11, a new Wi-Fi6E front-end module. Image used courtesy of Skyworks
Supporting the Wi-Fi 6E output power with a +19 dBm to -43 dB range, both devices include an integrated PA, logarithmic power detector, LNA with bypass, and T/R switch. Skyworks says the SKY85784-11 can extend range coverage by offering both a low EVM floor and a high linear output power that meets the regulatory limit.
Alternately, the SKY85780-11 front-end module is said to be “the only solution on the market to maximize distance and throughput within FCC maximum output power limit.”
New Protocols, New Designs
As wireless technology continues to advance, electrical engineers may continue to face unprecedented design challenges to support higher bandwidths and power demands. What changes have you seen front-end design undergo as new wireless protocols have rolled out? Share your thoughts in the comments below.
