The complexity of current 4G/5G phones comes from the need to cover multiple bands. Modern modems like the ones used in mobile phones are compatible with multiple transmission bands, including 3G, 4G LTE, Wi-Fi, and Bluetooth. The radio frequency front-end (RFFE) section of cellphone includes components like antennas, LNAs, filters, and switches. The usual arrangement is to divide the RFFE into sections for low bands (698-960 MHz), mid-band (1710-2200 MHz), and high-band (2400-3800 MHz). 5G would add another section. Filters are components required for dividing the frequency band. Filter main role is to selectively transmit and receive desired signals and greatly attenuating the other frequency components, reduce the interference of the signal.
To avoid cross talk and optimize the quality and throughput of each band, a dedicated analog filter is used for each of the bands. Good filters like surface acoustic wave (SAW) or bulk acoustic wave (BAW) types are essential to minimize cross talk and intermodulation distortion. In addition to the 2/3 / 4G signal Send and receive filtering, but also need to Wi-Fi, Bluetooth, GPS signal filtering, so a phone about 30 or so for different bands of the filter. Unlike general filter components which are based on electromagnetic (EM) signals, the Surface-acoustic-wave (SAW) and bulk-acoustic-wave (BAW) resonators, filters, oscillators, and delay lines are based on Acoustic waves. Since Acoustic waves have much shorter-wavelength it’s possible to create extremely small resonators, filters, oscillators, and delay lines for SAW structures that process higher-frequency electromagnetic (EM) signals.
The advantage of acoustic wave filters over electromagnetic filters is generally recognized as their small size resulting from the approximately five orders of magnitude reduction in the acoustic wave velocity. Bulk acoustic wave resonators have such unique advantages since they are at least an order of magnitude smaller than dielectric resonators or lumped elements, and possess much lower insertion loss than Surface Acoustic Wave devices. When compared to Surface Acoustic Wave devices, BAW resonators exhibit a lower frequency drift with temperature, a better power handling, and their technology can be made compatible with standard IC technology, hence moving a step closer to the one-chip radio concept.
Bulk Acoustic Wave (BAW) piezoelectric resonator is a device that has the potential for meeting the needs of modern wireless communication equipments. RF systems between 1 and 10 GHz can be targeted with such devices, which provide a high Qfactor. Qfactor offered by BAW is greater than that for on-chip LC tanks. In addition to the high QFactor BAW resonators also provide low volume, low cost, and a reasonable coupling coefficient. These properties are all essential when portability is required, since they contribute to a reduced power consumption and a greater compactness.
RF filters will be disruptor in the military RF and microwave industries. “The number of mobile devices is growing. As it does, frequency and bandwidth will continue to be limited. This significantly impacts everything from commercial applications like smartphones, Wi-Fi, and base stations to defense technologies like radar and [communications] systems. The industry will have to rely on RF filters such as BAW [bulk acoustic wave] and SAW [surface acoustic wave] to solve this issue, which will ultimately improve user experience and connectivity, says Roger Hall, General Manager”, says Defense & Aerospace for Qorvo
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