The filter is used to remove unwanted frequency components in the signal while preserving the required frequency components. The filter is basically divided into four types of low-pass, high-pass, band-pass, and band-stop (band reject) filters according to different ways of receiving or suppressing signals.
Today we don't talk about this. With the continuous evolution of acoustic wave filter technology, it will meet the challenges encountered in the global migration to 4G networks. Q Jun introduces two technologies for solving mobile device filtering: Surface Acous Wave Filter (SAW) and Bulk Acous Wave Filter (BAW).
SAW
SAW is widely used in 2G and 3G receiver front-ends, duplexers, and receive filters. It combines low insertion loss with good rejection to achieve high bandwidth and is only as large as conventional cavity and ceramic filters. The former is a fraction.
Advantage
The main advantage of SAW is its ability to meet the highest 1.9 GHz standard filter applications, including standard bands such as GSM, CDMA and 3G, as well as some 4 bands. Currently, wafer-level packaging and other technologies are used to reduce the volume of the surface acoustic wave filter, which allows filters and duplexers of multiple frequency bands to be integrated into one chip. This is all the more important as smartphones continue to be enriched.
limitation
At frequencies above about 1 GHz, the selectivity of such filters is reduced; at frequencies up to about 2.5 GHz, surface acoustic waves are limited to applications with medium performance requirements. In addition, SAW is very sensitive to temperature. When the temperature rises, the frequency response of the surface acoustic wave filter may drop by as much as 4 MHz. As the guard band becomes narrower and the specified operating temperature range for consumer devices is large (typically -20 ° C to 85 ° C), the impact of this limitation is increasing.
BAW
BAW delivers superior performance (higher quality factor) at higher frequency levels with lower insertion loss. By using bulk acoustic wave technology, it is possible to develop a narrow-band filter with extremely high edge slope and excellent suppression capability. This makes bulk acoustic waves the technology of choice for solving many interference problems.
Advantage
The operating frequency is about 1.5 GHz, making it complementary to surface acoustic wave technology (the latter is more efficient at lower frequencies). Bulk acoustic waves can be processed at frequencies up to 6 GHz and are used in new LTE bands with frequencies above 1.9 GHz. In addition, for LTE/Wi-Fi coexistence filters, bulk acoustic waves are also very effective.
The size of the bulk acoustic wave filter decreases with increasing frequency, making the bulk acoustic wave filter an ideal filter for the most demanding 3G and 4G applications. In addition, even at wide bandwidths, the design of bulk acoustic waves is much less sensitive to temperature changes.
As a feature-rich international handset, it may now be necessary to filter 2G, 3G and 4G transceivers in up to 15 bands, in addition to Wi-Fi, Bluetooth and Global Navigation Satellite System (GNSS). Statistics, such a phone may require up to 30 to 40 filters.
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