Surface acoustic wave filter apparatus and communication apparatus

• US 20020167378A1
• Filed: 04/17/2002
• Published: 11/14/2002
• Est. Priority Date: 04/18/2001
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Sawada, Yoichi
• Granted Patent: US 6,891,451 B2
• Time in Patent Office: Days
• US Class Current: 333/193
• CPC Class Codes: H03H 9/0071 the balanced terminals being on the same side of the tracks
• CPC Class Codes: H03H 9/0085 having four acoustic tracks

Abstract

A surface acoustic wave filter apparatus includes extensional-coupling-resonator-mode first through fourth SAW filter devices which are disposed on a piezoelectric substrate. Each SAW filter device includes three interdigital transducers (IDTs) arranged in a SAW propagating direction, and reflectors arranged such that they sandwich the IDTs therebetween. The SAW filter devices are provided with a balanced-to-unbalanced input/output function. The reflectors of the first and second SAW filter devices are different from those of the third and fourth SAW filter devices in at least one of the number, the pitch, the duty, and the thickness of the electrode fingers of the reflectors.

Claims

1. A surface acoustic wave filter apparatus comprising:

a piezoelectric substrate;

a surface acoustic wave filter device disposed on said piezoelectric substrate, said surface acoustic wave filter device including;

a plurality of interdigital transducers arranged in a direction in which a surface acoustic wave propagates; and

at least two reflectors arranged to reflect the surface acoustic wave propagating from each of the plurality of interdigital transducers to the corresponding interdigital transducer, said surface acoustic wave device being provided with a balanced-to-unbalanced conversion function;

wherein

the structure of at least one of the at least two reflectors is different from the structure of the other of the at least two reflectors.

2. A surface acoustic wave filter apparatus according to claim 1, wherein the structure of the at least one of the at least two reflectors is different from the structure of the other of the at least two reflectors in at least one of the number, the pitch, the duty, and the thickness of electrode fingers of the reflectors.

3. A surface acoustic wave filter apparatus according to claim 1, further comprising a plurality of the surface acoustic wave filter devices disposed on the piezoelectric substrate, wherein the reflectors of each of the plurality of the surface acoustic wave filter devices are different from each other.

4. A surface acoustic wave filter apparatus according to claim 1, wherein the piezoelectric substrate is a LiTaO₃ piezoelectric substrate.

5. A communication apparatus comprising the surface acoustic wave filter apparatus according to claim 1.

14. A communication apparatus comprising the surface acoustic wave filter apparatus according to claim 1.

6. A surface acoustic wave filter apparatus comprising:

a piezoelectric substrate;

a first surface acoustic wave filter device disposed on the piezoelectric substrate and including a plurality of interdigital transducers arranged in a direction in which a surface acoustic wave propagates, and reflectors arranged so as to sandwich the plurality of interdigital transducers therebetween;

a second surface acoustic wave filter device disposed on the piezoelectric substrate and including a plurality of interdigital transducers arranged in a direction in which a surface acoustic wave propagates, and reflectors arranged so as to sandwich the plurality of interdigital transducers therebetween, transmission phase characteristics of said second surface acoustic wave filter device being 180°

out of phase with transmission phase characteristics of said first surface acoustic wave filter device;

an unbalanced terminal for electrically connecting one terminal of said first surface acoustic wave filter device in parallel to one terminal of said second surface acoustic wave filter device; and

balanced terminals for electrically connecting the other terminal of said first surface acoustic wave filter device to the other terminal of said second surface acoustic wave filter device;

wherein

the structure of the reflectors of said first surface acoustic wave filter device is different from the structure of the reflectors of said second surface acoustic wave filter device.

7. A surface acoustic wave filter apparatus according to claim 6, wherein the reflectors of said first surface acoustic wave filter device are different from the reflectors of said second surface acoustic wave filter device in at least one of the number, the pitch, the duty, and the thickness of electrode fingers of the reflectors.

8. A surface acoustic wave filter apparatus according to claim 6, wherein the piezoelectric substrate is a LiTaO₃ piezoelectric substrate.

9. A communication apparatus comprising the surface acoustic wave filter apparatus according to claim 6.

10. A surface acoustic wave filter apparatus comprising:

a piezoelectric substrate;

first, second, and third surface acoustic wave filter devices disposed on the piezoelectric substrate, each of said first, second, and third surface acoustic wave filter devices including a plurality of interdigital transducers arranged in a direction in which a surface acoustic wave propagates, and reflectors arranged so as to sandwich the plurality of interdigital transducers therebetween;

a fourth surface acoustic wave filter device disposed on the piezoelectric substrate and including a plurality of interdigital transducers arranged in a direction in which a surface acoustic wave propagates, and reflectors arranged so as to sandwich the plurality of interdigital transducers therebetween, transmission phase characteristics of said fourth surface acoustic wave filter device being 180°

out of phase with transmission phase characteristics of said first, second, and third surface acoustic wave filter devices;

an unbalanced terminal for electrically connecting one terminal of a first group obtained by cascade-connecting said first and second surface acoustic wave filter devices in parallel to one terminal of a second group obtained by cascade-connecting said third and fourth surface acoustic wave filter devices; and

balanced terminals for electrically connecting the other terminal of the first group in series to the other terminal of the second group;

wherein

the structure of the reflectors of at least one of said first through fourth surface acoustic wave filter devices is different from the structure of the reflectors of the other surface acoustic wave filter devices.

11. A surface acoustic wave filter apparatus according to claim 10, wherein the structure of the reflectors of the first group is different from the structure of the reflectors of the second group.

12. A surface acoustic wave filter apparatus according to claim 10, wherein the structures of the reflectors are different among said first through fourth surface acoustic wave filter devices in at least one of the number, the pitch, the duty, and the thickness of electrode fingers of the reflectors.

13. A surface acoustic wave filter apparatus according to claim 10, wherein the piezoelectric substrate is a LiTaO₃ piezoelectric substrate.