Surface acoustic wave device and communication apparatus including the same

• US 20040077325A1
• Filed: 09/19/2003
• Published: 04/22/2004
• Est. Priority Date: 09/20/2002
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Takamine, Yuichi
• Granted Patent: US 7,116,189 B2
• Time in Patent Office: Days
• US Class Current: 455/286
• CPC Class Codes: H03H 9/0071 the balanced terminals being on the same side of the tracks
• CPC Class Codes: H03H 9/008 having three acoustic tracks H03H9/0085 takes precedence
• CPC Class Codes: H03H 9/0085 having four acoustic tracks
• CPC Class Codes: H03H 9/02771 Reflector banks
• CPC Class Codes: H03H 9/14582 the last fingers having a different pitch
• CPC Class Codes: H03H 9/6426 Combinations of the characteristics of different transducers

Abstract

A SAW device includes two surface-acoustic-wave filter elements arranged so as to have a balanced-to-unbalanced conversion function. The surface-acoustic-wave filter elements include two first reflectors and two second reflectors. In each surface-acoustic-wave filter element, three IDTs are arranged on a piezoelectric substrate in a direction in which surface acoustic waves are transmitted so as to be positioned between one first reflector and one second reflector. The first reflectors differ in structure from the second reflectors.

Claims

1. A surface acoustic wave device comprising:

a piezoelectric substrate; and

first and second surface-acoustic-wave filter elements arranged on said piezoelectric substrate so as to have a balanced-to-unbalanced conversion function, said first and second surface-acoustic-wave filter elements each including at least two interdigital transducers arranged along a propagation direction of surface acoustic waves, and a first reflector and a second reflector which are arranged such that said at least two interdigital transducers are arranged along the propagation direction between the first and second reflectors;

wherein

the first and second reflectors differ in structure, and in said first and second surface-acoustic-wave filter elements, the first reflectors have the same structure, and the second reflectors have the same structure.

2. A surface acoustic wave device according to claim 1, wherein a number of electrode fingers of said first reflector differs from a number of electrode fingers of said second reflector in the respective first and second surface-acoustic-wave filter elements.

3. A surface acoustic wave device according to claim 1, wherein a duty of said first reflector differs from a duty of said second reflector in the respective first and second surface-acoustic-wave filter elements.

4. A surface acoustic wave device according to claim 1, wherein an electrode-finger pitch of said first reflector differs from the electrode-finger pitch of said second reflector in the respective first and second surface-acoustic-wave filter elements.

9. A surface acoustic wave device according to claim 1, further comprising a cascade-connected surface-acoustic-wave filter element.

17. A communication apparatus including a surface acoustic wave device as described in claim 1.

5. A surface acoustic wave device comprising:

a piezoelectric substrate; and

first and second surface-acoustic-wave filter elements arranged on said piezoelectric substrate so as to have a balanced-to-unbalanced conversion function, said first and second surface-acoustic-wave filter elements each including at least two interdigital transducers arranged along a propagation direction of surface acoustic waves, and a first reflector and a second reflector which are arranged so that said at least two interdigital transducers are provided along the propagation direction between the first and second reflectors;

wherein

in each of said first and second surface-acoustic-wave filter elements, a first center-to-center distance of the adjacent electrode fingers between said first reflector and one interdigital transducer adjacent thereto differs from a second center-to-center distance of the adjacent electrode fingers between said second reflector and one interdigital transducer adjacent thereto; and

the first and second center-to-center distances of the first surface-acoustic-wave filter element is the same as the corresponding first and second center-to-center distances of the second surface-acoustic-wave filter element.

18. A communication apparatus including a surface acoustic wave device as described in claim 5.

6. A surface acoustic wave device comprising:

a piezoelectric substrate; and

first and second surface-acoustic-wave filter elements arranged on said piezoelectric substrate so as to have a balanced-to-unbalanced conversion function, said first and second surface-acoustic-wave filter elements each including at least two interdigital transducers arranged along a propagation direction of surface acoustic waves, and a first reflector and a second reflector which are arranged so that said at least two interdigital transducers are provided along the propagation direction between the first and second reflectors;

wherein

the first and second reflectors are weighted by apodization; and

in said first and second surface-acoustic-wave filter elements, the first reflectors have the same structure, and the second reflectors have the same structure.

19. A communication apparatus including a surface acoustic wave device as described in claim 6.

7. A surface acoustic wave device comprising:

a piezoelectric substrate; and

first and second surface-acoustic-wave filter elements arranged on said piezoelectric substrate so as to have a balanced-to-unbalanced conversion function, said first and second surface-acoustic-wave filter elements each including at least two interdigital transducers arranged along a propagation direction of surface acoustic waves, and a first reflector and a second reflector which are arranged so that said at least two interdigital transducers are provided along the propagation direction between the first and second reflectors;

wherein

in at least one portion of at least one of said first reflector and said second reflector, at least one of an electrode-finger width and an electrode-finger gap differs compared with surrounding electrode fingers; and

in said first and second surface-acoustic-wave filter elements, the first reflectors have the same structure, and the second reflectors have the same structure.

20. A communication apparatus including a surface acoustic wave device as described in claim 7.

8. A surface acoustic wave device comprising:

a piezoelectric substrate; and

first and second surface-acoustic-wave filter elements arranged on said piezoelectric substrate so as to have a balanced-to-unbalanced conversion function, said first and second surface-acoustic-wave filter elements each including at least two interdigital transducers arranged along a propagation direction of surface acoustic waves, and a first reflector and a second reflector which are arranged so that said at least two interdigital transducers are provided along the propagation direction between the first and second reflectors;

wherein

in at least one portion of at least one of said first reflector and said second reflector, a duty differs compared with surrounding electrode fingers; and

in said first and second surface-acoustic-wave filter elements, the first reflectors have the same structure, and the second reflectors have the same structure.

21. A communication apparatus including a surface acoustic wave device as described in claim 8.

10. A surface acoustic wave device comprising:

a piezoelectric substrate; and

first, second, third, and fourth surface-acoustic-wave filter elements arranged on said piezoelectric substrate so as to have a balanced-to-unbalanced conversion function, said first, second, third, and fourth surface-acoustic-wave filter elements each including at least two interdigital transducers arranged along a propagation direction of surface acoustic waves, and a set of reflectors arranged so that said at least two interdigital transducers are provided along the propagation direction between opposite reflectors of the set of reflectors;

wherein

the first and third surface-acoustic-wave filter elements are cascade-connected to each other, and the second and fourth surface-acoustic-wave filter elements are cascade-connected to each other;

the first and second surface-acoustic-wave filter elements have the same sets of reflectors, and the third and fourth surface-acoustic-wave filter elements have the same sets of reflectors; and

the sets of reflectors in the first and second surface-acoustic-wave filter elements differ in structure from the sets of reflectors in the third and fourth surface-acoustic-wave filter elements.

12. A surface acoustic wave device according to claim 10, wherein a number of electrode fingers of the reflector in the first surface-acoustic-wave filter element differs from a number of electrode fingers of the reflector in the third surface-acoustic-wave filter element, and a number of electrode fingers of the reflector in the second surface-acoustic-wave filter element differs from a number of electrode fingers of the reflector in the fourth surface-acoustic-wave filter element.

13. A surface acoustic wave device according to claim 10, wherein a duty of the reflector of the first surface-acoustic-wave filter element differs from a duty of the reflector of the third surface-acoustic-wave filter element, and a duty of the reflector of the second surface-acoustic-wave filter element differs from a duty of the reflector of the fourth surface-acoustic-wave filter element.

14. A surface acoustic wave device according to claim 10, wherein an electrode-finger pitch of the reflector of the first surface-acoustic-wave filter element differs from an electrode-finger pitch of the reflector of the third surface-acoustic-wave filter element, and an electrode-finger pitch of the reflector of the second surface-acoustic-wave filter element differs from an electrode-finger pitch of the reflector of the fourth surface-acoustic-wave filter element.

22. A communication apparatus including a surface acoustic wave device as described in claim 10.

11. A surface acoustic wave device comprising:

a piezoelectric substrate; and

first, second, third, and fourth surface-acoustic-wave filter elements arranged on said piezoelectric substrate so as to have a balanced-to-unbalanced conversion function, said first, second, third, and fourth surface-acoustic-wave filter elements each including at least two interdigital transducers arranged along a propagation direction of surface acoustic waves, and a set of reflectors arranged so that said at least two interdigital transducers are provided along the propagation direction between opposite reflectors of the set of reflectors;

wherein

the first and third surface-acoustic-wave filter elements are cascade-connected to each other, and the second and fourth surface-acoustic-wave filter elements are cascade-connected to each other;

the first and fourth surface-acoustic-wave filter elements have the same sets of reflectors, and the second and third surface-acoustic-wave filter elements have the same sets of reflectors; and

the sets of reflectors in the first and fourth surface-acoustic-wave filter elements differ in structure from the sets of reflectors in the second and third surface-acoustic-wave filter elements.

23. A communication apparatus including a surface acoustic wave device as described in claim 11.

15. A surface acoustic wave device comprising:

a piezoelectric substrate; and

first, second, third, and fourth surface-acoustic-wave filter elements arranged on said piezoelectric substrate so as to have a balanced-to-unbalanced conversion function, said first, second, third, and fourth surface-acoustic-wave filter elements each including at least two interdigital transducers arranged along a propagation direction of surface acoustic waves, and a set of reflectors arranged so that said at least two interdigital transducers are provided along the propagation direction between opposite reflectors of the set of reflectors;

wherein

the first and third surface-acoustic-wave filter elements are cascade-connected to each other, and the second and fourth surface-acoustic-wave filter elements are cascade-connected to each other;

a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the first surface-acoustic-wave filter element and one interdigital transducer adjacent thereto differs from a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the third surface-acoustic-wave filter element and one interdigital transducer adjacent thereto;

a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the second surface-acoustic-wave filter element and one interdigital transducer adjacent thereto differs from a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the fourth surface-acoustic-wave filter element and one interdigital transducer adjacent thereto;

a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the first surface-acoustic-wave filter element and one interdigital transducer adjacent thereto is equal to a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the second surface-acoustic-wave filter element and one interdigital transducer adjacent thereto; and

a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the third surface-acoustic-wave filter element and one interdigital transducer adjacent thereto is equal to a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the fourth surface-acoustic-wave filter element and one interdigital transducer adjacent thereto.

24. A communication apparatus including a surface acoustic wave device as described in claim 15.

16. A surface acoustic wave device comprising:

a piezoelectric substrate; and

first, second, third, and fourth surface-acoustic-wave filter elements arranged on said piezoelectric substrate so as to have a balanced-to-unbalanced conversion function, said first, second, third, and fourth surface-acoustic-wave filter elements each including at least two interdigital transducers arranged along a propagation direction of surface acoustic waves, and a set of reflectors arranged so that said at least two interdigital transducers are provided along the propagation direction between opposite reflectors of the set of reflectors;

wherein

the first and third surface-acoustic-wave filter elements are cascade-connected to each other, and the second and fourth surface-acoustic-wave filter elements are cascade-connected to each other;

a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the first surface-acoustic-wave filter element and one interdigital transducer adjacent thereto differs from a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the third surface-acoustic-wave filter element and one interdigital transducer adjacent thereto;

a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the second surface-acoustic-wave filter element and one interdigital transducer adjacent thereto differs from a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the fourth surface-acoustic-wave filter element and one interdigital transducer adjacent thereto;

a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the first surface-acoustic-wave filter element and one interdigital transducer adjacent thereto is equal to a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the fourth surface-acoustic-wave filter element and one interdigital transducer adjacent thereto; and

a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the second surface-acoustic-wave filter element and one interdigital transducer adjacent thereto is equal to a center-to-center distance of the adjacent electrode fingers between one of the reflectors in the third surface-acoustic-wave filter element and one interdigital transducer adjacent thereto.

25. A communication apparatus including a surface acoustic wave device as described in claim 16.