Browse Prior Art Database

Designing Surface Acoustic Wave Filters

IP.com Disclosure Number: IPCOM000087609D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Walker, EL: AUTHOR

Abstract

This design sets forth a way of obtaining maximum aperture sizes and minimum weighting values in the design of surface acoustic wave (SAW) devices.

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Designing Surface Acoustic Wave Filters

This design sets forth a way of obtaining maximum aperture sizes and minimum weighting values in the design of surface acoustic wave (SAW) devices.

In the course of designing bandpass filters using SAW devices, it is commonly necessary to weight the apertures on one or both transducers to achieve a desired performance. The weighting is accomplished by arranging the length of the teeth in the comb-shaped electrodes of the transducer in accordance with the desired mathematical weighting function. The aperture relates to the overlap between adjacent interleaved teeth.

Referring to Fig. 1, it can be seen that the input transducer 10 made up of electrodes 12 and 14 having interleaved teeth 16 has a weighting W(n) which is equal to a constant. However, the output transducer 18 consisting of electrodes 20 and 22 each having teeth 19 which are varied in length in accordance with the weighting W(n). Actually, the most common implementation of weighting in bandpass filters, as illustrated in Fig. 1, is to vary the beam width of the finger pairs (amount of overlap of teeth) in accordance with the normalized values of A(n), a mathematically obtained function that satisfies the boundary conditions in the filter response specification.

For a uniformly sampled filter designed (Fig. 2) to give a symmetrical response around some center frequency f(o) the A(n) values are the terms, and n=2N-1 is the number of finger or teeth pairs. N is determined from the ripple and rejection level specification. For the filter response shape shown in Fig. 2 ...