Technique for capacitively voltage weighting interdigital surface acoustic wave transducers

Abstract

A simple method is presented by which the voltage between electrodes on an interdigital surface acoustic wave (SAW) transducer is varied by means of capacitive voltage division. Using this technique, a capacitor is added in series with the capacitance of an electrode pair through the use of a single photolithographic mask. The capacitance values are determined by geometry alone. This method permits voltage weighting both transducers of a device, and it minimizes the effects of diffraction. Experimental results are presented in which the sidelobes in a SAW filter have been reduced to 45 dB below the passband level.