New design techniques for SAW filters using slanted-finger IDTs

Abstract

The authors describe two design techniques for slanted-finger interdigital transducers (IDTs) which could not be designed using conventional techniques. One technique provides a large stopband attenuation: individual fingers or groups of slanted-fingers are withdrawn from the selected portions of the IDT. The other technique realizes a nonlinear phase response: the center-to-center distance between transmitting and receiving ITDs is varied along the axis normal to the surface acoustic wave (SAW) propagation axis. Two examples of filters, fabricated on x-112y LiTaO/sub 3/, are shown with about a 30% fractional bandwidth and a 19 MHz center frequency. One filter has a 45-dB stop-band attenuation, a 1.10 shape factor, and +or-0.05-dB passband ripples. The other filter has a nonlinear phase response which equalizes the phase response of an LC filter. This filter achieves a group delay distortion of less than +or-10 ns.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>