What is a SAW Filter?

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- everything RF

Apr 4, 2019

Surface Acoustic Wave Filters or SAW Filters are compact, low-cost RF filters that can be used in a wide range of applications up to 3 GHz. SAW filters operate by converting electrical energy into acoustic or mechanical energy on a piezoelectric material. To do so these filters uses interdigital transducers (IDTs). The IDTs have interleaved metal electrodes on either end of the device which converts an electrical signal into an acoustic wave and then back to an electrical signal.

Once the electrical energy is converted into acoustic waves, the waves travel across the surface of an elastic, piezoelectric material with an amplitude decaying into the substrate material, such as quartz, lithium tantalite (LiTaO3) or lithium niobate (LiNbO3). This decay is what causes the insertion loss in SAW Filters.

Surface Acoustic Wave (SAW) filters are best suited for applications up to 3 GHz. The filter selectivity starts to decline above 1.5 GHz, and at about 3 GHz their use is limited to applications that have modest performance requirements.

The center frequency of a SAW filter is impacted considerably by temperature variations. Except for the Quartz substrate, the center frequency of a filter will shift upwards at lower temperatures and downwards at higher temperatures in a linear fashion. To compensate for these shifts in frequency, temperature shift components are often added to SAW filters. Another option would be to use TC-SAW Filters i.e. Temperature Compensated SAW Filters.