A Design Algorithm for Arbitrary Phase and Amplitude Surface Acoustic Wave Filters

Abstract

<p>The subject of this study is the development of a computer-aided-design tool that filter designers could use to obtain nonlinear phase and nonsymmetric amplitude responses for surface acoustic wave devices. To accomplish this, a design algorithm was developed that uses a Fast Fourier Transform to realize the time domain transform of the frequency domain specifications required by the designer. From this time domain solution an interdigital transducer (IDT) is synthesized that will approximate the design specifications. The next step in the algorithm is to analyse the synthesized IDT using an accurate charge distribution model for the IDT (the charge distribution model is developed in this thesis which gives the frequency domain response for the IDT). The frequency response is then compared to the input specifications so as to generate an error function. This error function is then used to predistort the input frequency domain specifications and the whole synthesis/analysis procedure is repeated iteratively until an acceptable solution is obtained. The algorithm is programmed and used to design 2 filters (3 separate IDT designs) for the nonlinear phase and nonsymmetric amplitude specifications for television intermediate frequency (TVIF) specifications. Using these designs, two filters were fabricated and tested to show the validity of the algorithm.</p>