SAW Filters are electromechanical devices commonly used in radio frequency applications. Electrical signals are converted a mechanical wave in a device constructed of a piezoelectric crytal or cermaic; this wave is delayed as it propagates a across the device, before being converted back to an electrical signal by further electrodes.
The delayed outputs are recombined to produce a direct analong implementation of a finite impulse reponse filter.
This hybrid filtering technique is also found in an analog sampled filter. SAW filters are limited to frequencies up to 3GHz.
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