SAW filter

SAW filter

(Surface Acoustic Wave filter) A semiconductor device that is used to filter out desired frequencies. Widely used in mobile phones to filter both RF and IF frequencies, a SAW filter uses the piezoelectric effect to turn the input signal into vibrations that are turned back into electrical signals in the desired frequency range.

Two sets of metal electrodes like teeth on a comb are adhered to a quartz crystal and spaced apart (in microns) based on the required frequencies. As few as five and as many as 5,000 electrodes are used. An intriguing analogy from Bruce Thomas at Sawtek, a subsidiary of TriQuint Semiconductor, is that the first set of electrodes is like throwing a large log into a pond, which makes huge waves that cause little sticks to bounce out at the other side (second set).

TC-SAW and BAW
SAW filters are sensitive to high temperatures, and temperature-compensated SAW (TC-SAW) filters were designed to retain their integrity under such conditions. However, TC-SAWs do not support the higher LTE frequencies, but bulk acoustic wave (BAW) filters do. As a result, SAW filters are often used for lower frequencies, while BAWs, which are twice as costly, are used for the high end. See RF filter.
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References in periodicals archive ?
This SAW filter is designed for use in a global navigation satellite system.
By using a balanced output SAW filter instead of a single output one, the RF designer can suppress the use of the transformer and impedance networks (see Figure 2).
The model VS-500 SAW stabilized, voltage-controlled oscillator operates at the fundamental frequency of the internal SAW filter.
The signal is then upconverted to IF and the I and Q channels are combined and moved off chip to the external SAW filter.
A transversal SAW filter generally consists of input and output transducers deposited on a highly polished piezoelectric substrate such as quartz, lithium tantalate or lithium niobate.
Eigen functions for the SAW filter design (first used by DeVries[1]) were simple sinc functions in the frequency domain whose inverse Fourier transforms were cosine bursts of particular durations.