Every Wi-Fi generation since Wi-Fi 4 has tightened its demands on signal quality, and the RF front end has quietly paid for it in range, power, and calibration effort. Dr Ali Fard – who worked on one of the first Wi-Fi chips with digital predistortion – now argues that the correction loop has reached its limits and that the fix belongs in the amplifier itself.
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The previous parts of this series have examined why front-end modules matter, why filtering is becoming more difficult, how PA linearity and digital predistortion (DPD) affect RF architecture, and why the entire Wi-Fi radio chain ultimately needs to be designed as a system. So who supplies these technologies? The answer reveals a market that is becoming increasingly diverse.
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Wi-Fi APs increasingly need to support many frequency bands, multiple spatial streams, wide channels, high-order modulation, simultaneous transmissions, Bluetooth and sometimes cellular radios – all within tight constraints on size, cost and power consumption.Meanwhile, the RF chain needs to preserve extremely demanding signal quality from the Wi-Fi chipset all the way to the antenna. This makes RF front-end integration one of the less visible – but increasingly important.
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Digital pre-distortion, or DPD, offers one way to improve that trade-off. But DPD also adds digital processing, calibration, control, and integration requirements involving both the Wi-Fi chipset and the RF front end. There is another possibility: Improve the underlying analog RF architecture so that less digital correction is required in the first place. This is the approach being pursued by QuantalRF.
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Wi-Fi radios have a deceptively simple job: Transmit and receive radio signals within the frequencies allocated to Wi-Fi. In practice, however, the RF environment surrounding a Wi-Fi radio is crowded with signals that the receiver does not want – and some of the strongest unwanted signals may originate from radios inside the same device. This is where RF filters become essential.
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A key building block of the RF front end is the front-end module, or FEM. As Wi-Fi has expanded across the 2.4 GHz, 5 GHz, and 6 GHz bands – and as Wi-Fi signals have become wider and more demanding – the performance of these components has become increasingly important.
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