Introduce the SAW Filter

Surface acoustic wave filter (SAWF) is made of quartz, lithium niobate and barium titanate crystals with piezoelectric effect. The so-called piezoelectric effect is that when the crystal is subjected to mechanical action, it will produce an electric field proportional to the pressure; When the crystal with piezoelectric effect is affected by electric signal, it will produce elastic deformation and emit mechanical wave (sound wave), which can convert electric signal into acoustic signal. Because this kind of sound wave only propagates on the crystal surface, it is called surface acoustic wave.

The characteristics of SAW filter

a. The frequency response is flat, the roughness is only ± 0.3 - ± 0.5dB, and the group delay is ± 30 - ± 50ns; 

b. SAWF has good rectangle coefficient, and the out of band rejection can reach more than 40dB;

c. Although the insertion loss is as high as 25-30db, the level loss can be compensated by an amplifier. Surface acoustic wave filter has the characteristics of frequency selection, which depends on the shape, spacing, cross length and number of electrodes of inter digital transducer. As long as the design is reasonable, the near ideal amplitude frequency characteristics of intermediate frequency can be obtained.

d. The saw filter has the advantages of small volume, light weight, reliable performance and no complex adjustment.

Application

Although the surface acoustic wave filter (swaf) is an analog device, it is widely used in many fields because of its good filtering characteristics. Especially in the cable TV system, the image if filter, sound filter, channel residual sideband filter and other swaf devices are the key to realize the adjacent frequency transmission. In addition, the front-end filter in GPS receiver is widely used because of its strong anti-interference ability.