Surface acoustic wave filter
First Claim
1. A surface acoustic wave (SAW) filter having a piezoelectric substrate and a conductive transducer formed over said piezoelectric substrate, wherein:
- said transducer has first and second bus bars arranged in parallel at a prescribed interval from each other;
a plurality of pairs of first electrode fingers having the same lengths, vertically extending from said first bus bar and arranged at prescribed intervals in the lengthwise direction of said first bus bar;
a plurality of pairs of second electrode fingers having the same lengths, vertically extending from said second bus bar, arranged at said prescribed intervals in the lengthwise direction of said second bus bar, the tips of these paired second electrode fingers being positioned opposite to those of said paired first electrode fingers;
a plurality of first weighted electrode pairs positioned between two adjacent pairs of said first electrode fingers, each pair of said first weighted electrodes comprising a pair of first electrode sections whose lengths of overlap with said paired second electrode fingers are determined by the negative tap coefficients of an FIR filter having a desired lowpass characteristic and a pair of second electrode sections positioned on the elongations of these first electrode sections, one end of each such second electrode section being connected to the first bus bar; and
a plurality of second weighted electrode pairs positioned between two adjacent pairs of said second electrode fingers, each pair comprising a pair of third electrode sections positioned between two opposite ones of said first electrode pairs, whose lengths of overlap with said paired first electrodes are determined by the positive tap coefficients of said FIR filter, and a pair of fourth electrode sections positioned on the elongations of said electrode sections, one end of each such fourth electrode section being connected to the second bus bar.
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Accused Products
Abstract
A surface acoustic wave (SAW) filter has a piezoelectric substrate and a conductive transducer formed over the substrate. The transducer has first and second bus bars arranged in parallel at a prescribed interval from each other, a plurality of pairs of first electrode fingers having the same lengths, and a plurality of pairs of second electrode fingers having the same lengths. The tips of the second electrode fingers are positioned opposite those of the first electrode fingers. The transducer also has first and second weighted electrode pairs positioned between two adjacent pairs of the first electrode fingers and two adjacent pairs of the second electrode fingers, respectively. Each pair of first weighted electrodes has a pair of first electrode sections whose lengths of overlap with the paired second electrode fingers are determined by the negative tap coefficients of an FIR filter having a desired low pass characteristic and a pair of second electrode sections positioned on the elongations of these first electrode sections, one end of each such second electrode section been connected to the first bus bar. The second weighted electrode pairs are similarly formed, but the lengths of overlap are determined by the positive tap coefficients of the FIR filter.
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Citations
14 Claims
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1. A surface acoustic wave (SAW) filter having a piezoelectric substrate and a conductive transducer formed over said piezoelectric substrate, wherein:
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said transducer has first and second bus bars arranged in parallel at a prescribed interval from each other; a plurality of pairs of first electrode fingers having the same lengths, vertically extending from said first bus bar and arranged at prescribed intervals in the lengthwise direction of said first bus bar; a plurality of pairs of second electrode fingers having the same lengths, vertically extending from said second bus bar, arranged at said prescribed intervals in the lengthwise direction of said second bus bar, the tips of these paired second electrode fingers being positioned opposite to those of said paired first electrode fingers; a plurality of first weighted electrode pairs positioned between two adjacent pairs of said first electrode fingers, each pair of said first weighted electrodes comprising a pair of first electrode sections whose lengths of overlap with said paired second electrode fingers are determined by the negative tap coefficients of an FIR filter having a desired lowpass characteristic and a pair of second electrode sections positioned on the elongations of these first electrode sections, one end of each such second electrode section being connected to the first bus bar; and a plurality of second weighted electrode pairs positioned between two adjacent pairs of said second electrode fingers, each pair comprising a pair of third electrode sections positioned between two opposite ones of said first electrode pairs, whose lengths of overlap with said paired first electrodes are determined by the positive tap coefficients of said FIR filter, and a pair of fourth electrode sections positioned on the elongations of said electrode sections, one end of each such fourth electrode section being connected to the second bus bar. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A surface acoustic wave (SAW) filter having a piezoelectric substrate and a conductive transducer set formed over said piezoelectric substrate, wherein:
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said transducer set has a first transducer, second and third transducers arranged in parallel to each other, and a multistrip coupler for coupling said first transducer to said second and third transducers; said first transducer has first and second bus bars arranged in parallel at a prescribed interval from each other; a plurality of pairs of first electrode fingers having the same lengths, vertically extending from said first bus bar and arranged at prescribed intervals in the lengthwise direction of said first bus bar; a plurality of pairs of second electrode fingers having the same lengths, vertically extending from said second bus bar, arranged at said prescribed intervals in the lengthwise direction of said second bus bar, the tips of these paired second electrode fingers positioned opposite to those of said paired first electrode fingers; a plurality of first weighted electrode pairs positioned between two adjacent pairs of said first electrode fingers, each pair of said first weighted electrodes comprising a pair of first electrode sections whose lengths of overlap with said paired second electrode fingers are determined by the negative tap coefficients of an FIR filter having a desired lowpass characteristic and a pair of second electrode sections positioned on the elongations of these first electrode sections, one end of each such second electrode section being connected to the first bus bar; a plurality of second weighted electrode pairs positioned between two adjacent pairs of said second electrode fingers, each pair comprising a pair of third electrode sections positioned between two opposite ones of said first electrode pairs, whose lengths of overlap with said paired first electrodes are determined by the positive tap coefficients of said FIR filter, and a pair of fourth electrode sections positioned on the elongations of said electrode sections, one end of each such fourth electrode section being connected to the second bus bar; said second transducer has exactly the same structure as said first transducer; and said third transducers includes electrode fingers having the same width and arranged at the same intervals as the electrode fingers of said first transducer, each such electrode finger being weighted according to the tap coefficient of a bandpass type FIR filter. - View Dependent Claims (10, 11, 12, 13, 14)
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Specification