What Is Surface Acoustic Wave Filter?

- Jul 18, 2018-

The surface acoustic wave filter is made of a piezoelectric effect of quartz, lithium niobate, and barium titanate crystal. The so-called piezoelectric effect is a phenomenon in which an electric field proportional to the pressure is generated when the crystal is mechanically acted upon. A crystal having a piezoelectric effect, when subjected to an electrical signal, also undergoes an elastic deformation to emit a mechanical wave (sound wave), thereby converting an electrical signal into an acoustic signal. Since this sound wave propagates only on the surface of the crystal, it is called a surface acoustic wave. The surface acoustic wave filter is abbreviated as SAWF. The surface acoustic wave filter has the advantages of small size, light weight, reliable performance and no need for complicated adjustment. It is a key device for implementing adjacent frequency transmission in cable TV systems. The surface acoustic wave filter is characterized by: (1) the frequency response is flat, the unevenness is only ±0.3-±0.5 dB, and the group delay is ±30-±50 ns. (2) SAWF has a good rectangular coefficient and the out-of-band rejection can reach more than 40dB. (3) Although the insertion loss is as high as 25-30dB, the amplifier can compensate for the level loss. The surface acoustic wave filter includes a surface acoustic wave television image IF filter, a television sound filter, and a TV channel vestigial sideband filter.

 

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