Ladder filter having edge reflection type saw resonators

A ladder filter comprising:

• a first piezoelectric substrate having a pair of end surfaces which are substantially parallel with each other;
• a second piezoelectric substrate having a pair of end surfaces which are substantially parallel with each other;
• a plurality of series arm resonators connected in series to define a series arm of a ladder circuit, each series arm resonator including a edge-reflection surface acoustic wave resonator which includes an interdigital transducer having a plurality of electrode fingers and utilizes a shear horizontal surface acoustic wave, the plurality of series arm resonators being arranged on the first piezoelectric substrate along a length direction of the first piezoelectric substrate such that a pair of outermost electrode fingers of each series arm resonator are flush with the pair of end surfaces of the first piezoelectric substrate, respectively;
• and
• a plurality of parallel arm resonators, each connected in parallel between the series arm and a ground potential to define a parallel arm of the ladder circuit and including an edge-reflection surface acoustic wave resonator which includes an interdigital transducer having a plurality of electrode fingers and utilizes a shear horizontal surface acoustic wave, the plurality of parallel arm resonators including a first group of at least two parallel arm resonators which are arranged on the second piezoelectric substrate along a length direction of the second piezoelectric substrate such that a pair of outermost electrode fingers of each parallel arm resonator of the first group are flush with the pair of end surfaces of the second piezoelectric substrate, respectively.

A ladder filter comprising:

• a piezoelectric substrate with a pair of end surfaces which are substantially parallel to each other and, the piezoelectric substrate having a groove structure extending substantially parallel to the pair of end surfaces so as to define first and second main regions between the pair of end surfaces of the piezoelectric substrate and corresponding side surfaces of the groove structure;
• a plurality of series arm resonators connected in series to define a series arm of a ladder circuit, each series arm resonator including an edge-reflection surface acoustic wave resonator which includes an interdigital transducer having a plurality of electrode fingers and utilizes a shear horizontal surface acoustic wave, the plurality of series arm resonators being arranged on the first main region of the piezoelectric substrate along a length direction of the first main region such that a pair of outermost electrode fingers of each series arm resonator are flush with one of the end surfaces of the piezoelectric substrate and one of the side surfaces of the groove structure;
• and
• a plurality of parallel arm resonators, each connected in parallel between the series arm and a ground potential to define a parallel arm of the ladder circuit and including an edge-reflection surface acoustic wave resonator which includes an interdigital transducer having a plurality of electrode fingers and utilizes a shear horizontal surface acoustic wave, the plurality of parallel arm resonators including a first group of at least two parallel arm resonators which are arranged at the second main region of the piezoelectric substrate along a length direction of the second main region such that a pair of outermost electrode fingers of each parallel arm resonator of the first group are flush with the other end surface of the piezoelectric substrate and the other side surface of the groove structure.

A ladder filter comprising:

• a piezoelectric substrate having a pair of end surfaces which are substantially parallel to each other and, the piezoelectric substrate having first and second groove structures each of which has a pair of side surfaces, respectively and extend substantially parallel to the pair of end surfaces so as to define a first main region between the two groove structures, a second main region between one end surface of the piezoelectric substrate and the first groove structure and a third main region between the other end surface of the piezoelectric substrate and the second groove structure;
• a plurality of series arm resonators connected in series to define a series arm of a ladder circuit, each series arm resonator including an edge-reflection surface acoustic wave resonator which includes an interdigital transducer having a plurality of electrode fingers and utilizes a shear horizontal surface acoustic wave, the plurality of series arm resonators being arranged on the first main region of the piezoelectric substrate along a length direction of the first main region such that a pair of outermost electrode fingers of each series arm resonator are flush with the respective side surfaces of the first and second groove structures;
• and
• a plurality of parallel arm resonators, each connected in parallel between the series arm and a ground potential to define a parallel arm of the ladder circuit and including an edge-reflection surface acoustic wave resonator which includes an interdigital transducer having a plurality of electrode fingers and utilizes a shear horizontal surface acoustic wave, the plurality of parallel arm resonators including a first group of at least two parallel arm resonators and a second group of at least two parallel arm resonators, the first group of the parallel arm resonators are arranged on the second main region of the piezoelectric substrate such that a pair of outermost electrode fingers of each parallel arm resonator of the first group are respectively flush with one of the end surfaces of the piezoelectric substrate and the other side surface of the first groove structure, the second group of the parallel arm resonators are arranged on the third main region of the piezoelectric substrate such that a pair of outermost electrode fingers of each parallel arm resonator of the second group are respectively flush with the other end surface of the piezoelectric substrate and the other side surface of the second groove structure.