Time Domain Analysis of SAW Filters.

摘要

A Surface Acoustic Wave (SAW) device consists of two transducers with interleaved aluminum fingers on a piezoelectric substrate. The input transducer is implemented with fingers of equal length, while the output transducer has fingers with varied overlap. The filter operates by electrically exciting the input transducer which through the piezoelectric effect causes a surface wave along with other modes to propagate toward the output transducer. There the wave is transformed back into an electrical signal. The output transducer works in a manner similar to a digital filter and can be modeled as a tapped delay line of N fingers where (1) each finger is a delta function generator-detector of surface waves, (2) the constant propagation time between fingers is the unit delay time t, (3) the variable finger overlap (apodization) is proportional to an attenuator weight Wk and (4) the relative direction of overlap with respect to the direction of propagation determines the relative sign of that tap. (Author)