| 摘要 |
A cascaded SAW filter system includes first and second SAW filters (12a, 12b) each including an input transducer (36, 36') and an output transducer (37, 37') on a piezoelectric substrate (38, 38'). Group delay and pass band ripples associated with a time spur at TD' away from the main signal of the second filter (12b) cancel the group delay and pass band ripples associated with a time spur at TD away from the main signal of the first filter (12a) because: 1) the input and output transducers (36', 37') of the second filter (12a) are offset from those of the first filter (12a); 2) the center frequency (f0') of the second filter (12b) is offset from the center frequency (f0) of the first filter (12a); 3) the perturbation region (P1) of the first filter (12a) is different from the perturbation region (P2) of the second filter (12b) or 3) a combination of 1), 2) and/or 3. The associated time spur echo of the cascaded response will also be canceled. Also, time spurs due to reflections from the ends of the input and output transducers of the first and second filters (12a, 12b) can be cancelled by adding dummy fingers (36a, 37a) at each end of the input arid output transducers of the second filter.
|
