Surface acoustic wave filter

• US 6,972,643 B2
• Filed: 06/26/2002
• Issued: 12/06/2005
• Est. Priority Date: 06/29/2001
• Status: Expired due to Term

• Current Assignee: Skyworks Filter Solutions Japan Co., Ltd. (Skyworks Solutions Incorporated)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Nakamura, Hiroyuki, Yamada, Toru, Seki, Shunichi, Tsunekawa, Akio, Nakaya, Shinobu
• Primary Examiner(s): Summons, Barbara
• Application Number:
  US10/362,903
• Publication Number:
  US 20040108918A1
• Time in Patent Office: 1,259 Days
• Field of Search: 333193-196, 333/133, 310/313.B, 310/313.D
• US Class Current: 333/195
• CPC Class Codes: H03H 9/0028 using surface acoustic wave devices
• CPC Class Codes: H03H 9/0042 the balanced terminals being on opposite sides of the track
• CPC Class Codes: H03H 9/14582 the last fingers having a different pitch
• CPC Class Codes: H03H 9/25 Constructional features of resonators using surface acoustic waves devices for manipulating acoustic surface waves in general G10K11/36
• CPC Class Codes: H03H 9/643 the transfer characteristic being determined by reflective or coupling array characteristics
• CPC Class Codes: H03H 9/6433 Coupled resonator filters
• CPC Class Codes: H03H 9/6436 having one acoustic track only

Abstract

A longitudinally coupled surface acoustic wave filter includes a first, second and third IDT electrodes and a first and second reflector electrodes on a piezoelectric substrate. The IDT electrodes each include a primary excitation region having λ/2 electrode finger pitches, where λ is the wavelength of a surface acoustic wave. The primary excitation region is phase-shifted by a certain amount in accordance with a desired passband frequency response. The IDT electrodes further include a plurality of secondary excitation regions each having electrode finger pitches different from the λ/2 pitches. All of the electrode finger pitches of the surface acoustic wave filter thus range from 0.8λ/2 to 1.2λ/2, so that a loss increase caused by discontinuity between the IDT electrodes is prevented.

Claims

1. A longitudinally coupled surface acoustic wave filter comprising:

a piezoelectric substrate; and

a plurality of interdigital transducer electrodes (IDT electrodes) and a plurality of reflector electrodes disposed on the piezoelectric substrate,

wherein each of the IDT electrodes is an interdigital electrode including a plurality of opposed electrode fingers,

wherein the IDT electrodes and the reflector electrodes are arranged in close relation along a propagation direction of a surface acoustic wave,

wherein each of the IDT electrodes includes a primary excitation region having λ

/2 electrode finger pitches, where λ

is a wavelength of the surface acoustic wave,

wherein the primary excitation region of at least one of the IDT electrodes is phase-shifted from the primary excitation region of another IDT electrode by a certain amount in accordance with a desired passband frequency response, and

wherein at least one of a condition that at least one of the IDT electrodes includes, on a side thereof adjacent to another IDT electrode, a secondary excitation region having electrode finger pitches different from the λ

/2 pitches, and a condition that at least one of the reflector electrodes having electrode finger pitches different from the λ

/2 pitches is disposed between two of the IDT electrodes is established,

the plurality of IDT electrodes includes a first IDT electrode and a second IDT electrode adjacent to the first IDT electrode,

the reflector electrodes include a first reflector electrode adjacent to the first IDT electrode and a second reflector electrode adjacent to the second IDT electrode,

the respective primary excitation regions of the first and second IDT electrodes are phase-shifted from each other by the certain amount in accordance with the desired passband frequency response, and

the first and second IDT electrodes include, on the respective adjacent sides of the first and second IDT electrodes, respective secondary excitation regions each having the electrode finger pitches different from the λ

/2 pitches,

wherein the electrode finger pitches of at least one of the secondary excitation regions are all equal.

2. The surface acoustic wave filter according to claim 1, wherein all of the electrode finger pitches of the surface acoustic wave filter fall within a range of 0.8λ

/2 to 1.2λ

/2.

3. The surface acoustic wave filter according to claim 1, wherein the surface acoustic wave is a leaky surface acoustic wave.

4. A longitudinally coupled surface acoustic wave filter comprising:

a piezoelectric substrate; and

a plurality of interdigital transducer electrodes (IDT electrodes) and a plurality of reflector electrodes disposed on the piezoelectric substrate,

wherein each of the IDT electrodes is an interdigital electrode including a plurality of opposed electrode fingers,

wherein the IDT electrodes and the reflector electrodes are arranged in close relation along a propagation direction of a surface acoustic wave,

wherein each of the IDT electrodes includes a primary excitation region having λ

/2 electrode finger pitches, where λ

is a wavelength of the surface acoustic wave,

wherein the primary excitation region of at least one of the IDT electrodes is phase-shifted from the primary excitation region of another IDT electrode by a certain amount in accordance with a desired passband frequency response, and

wherein at least one of a condition that at least one of the IDT electrodes includes, on a side thereof adjacent to another IDT electrode, a secondary excitation region having electrode finger pitches different from the λ

/2 pitches, and a condition that at least one of the reflector electrodes having electrode finger pitches different from the λ

/2 pitches is disposed between two of the IDT electrodes is established,

the plurality of IDT electrodes includes a first and second IDT electrodes,

at least one of the reflector electrodes is disposed between the first and second IDT electrodes,

the respective primary excitation regions of the first and second IDT electrodes are phase-shifted from each other by the certain amount in accordance with the desired passband frequency response, and

the at least one reflector electrode has electrode finger pitches different from the λ

/2 pitches,

wherein the electrode finger pitches of the at least one reflector electrode include two or more different kinds of electrode finger pitches.

5. A longitudinally coupled surface acoustic wave filter comprising:

a piezoelectric substrate; and

a plurality of interdigital transducer electrodes (IDT electrodes) and a plurality of reflector electrodes disposed on the piezoelectric substrate,

wherein each of the IDT electrodes is an interdigital electrode including a plurality of opposed electrode fingers,

wherein the IDT electrodes and the reflector electrodes are arranged in close relation along a propagation direction of a surface acoustic wave,

wherein each of the IDT electrodes includes a primary excitation region having λ

/2 electrode finger pitches, where λ

is a wavelength of the surface acoustic wave,

wherein the primary excitation region of at least one of the IDT electrodes is phase-shifted from the primary excitation region of another IDT electrode by a certain amount in accordance with a desired passband frequency response, and

wherein at least one of a condition that at least one of the IDT electrodes includes, on a side thereof adjacent to another IDT electrode, a secondary excitation region having electrode finger pitches different from the λ

/2 pitches, and a condition that at least one of the reflector electrodes having electrode finger pitches different from the λ

/2 pitches IS disposed between two of the IDT electrodes is established,

the plurality of IDT electrodes includes a first and second IDT electrodes,

at least one of the reflector electrodes is disposed between the first and second IDT electrode,

the respective primary excitation regions of the first and second IDT electrodes are phase-shifted from each other by the certain amount in accordance with the desired passband frequency response, and

the at least one reflector electrode has electrode finger pitches different from the λ

/2 pitches,

wherein the electrode finger pitches of the reflector electrode differ from one another and increase stepwise.

6. A longitudinally coupled surface acoustic wave filter comprising:

a piezoelectric substrate; and

a plurality of interdigital transducer electrodes (IDT electrodes) and a plurality of reflector electrodes disposed on the piezoelectric substrate,

wherein each of the IDT electrodes is an interdigital electrode including a plurality of opposed electrode fingers,

wherein the IDT electrodes and the reflector electrodes are arranged in close relation along a propagation direction of a surface acoustic wave,

wherein each of the IDT electrodes includes a primary excitation region having λ

/2 electrode finger pitches, where λ

is a wavelength of the surface acoustic wave,

wherein the primary excitation region of at least one of the IDT electrodes is phase-shifted from the primary excitation region of another IDT electrode by a certain amount in accordance with a desired passband frequency response, and

wherein at least one of a condition that at least one of the IDT electrodes includes, on a side thereof adjacent to another IDT electrode, a secondary excitation region having electrode finger pitches different from the λ

/2 pitches, and a condition that at least one of the reflector electrodes having electrode finger pitches different from the λ

/2 pitches is disposed between two of the IDT electrodes is established,

the plurality of IDT electrodes includes a first, second and third IDT electrodes,

the plurality of reflector electrodes includes a first and second reflector electrodes,

the second IDT electrode is located on a first side of the first IDT electrode across the first reflector electrode,

the third IDT electrode is located on a second side of the first IDT electrode across the second reflector electrode,

the primary excitation region of the first IDT electrode is phase-shifted from the respective primary excitation regions of the second and third IDT electrodes by the certain amount in accordance with the desired passband frequency response, and

each of the first and second reflector electrodes has electrode finger pitches different from the λ

/2 pitches,

wherein the electrode finger pitches of at least one of the first and second reflector electrodes include two or more different kinds of electrode finger pitches.

7. A longitudinally coupled surface acoustic wave filter comprising:

a piezoelectric substrate; and

a plurality of interdigital transducer electrodes (IDT electrodes) and a plurality of reflector electrodes disposed on the piezoelectric substrate,

wherein each of the IDT electrodes is an interdigital electrode including a plurality of opposed electrode fingers,

wherein the IDT electrodes and the reflector electrodes are arranged in close relation along a propagation direction of a surface acoustic wave,

wherein each of the IDT electrodes includes a primary excitation region having λ

/2 electrode finger pitches, where λ

is a wavelength of the surface acoustic wave,

wherein the primary excitation region of at least one of the IDT electrodes is phase-shifted from the primary excitation region of another IDT electrode by a certain amount in accordance with a desired passband frequency response, and

wherein at least one of a condition that at least one of the IDT electrodes includes, on a side thereof adjacent to another IDT electrode, a secondary excitation region having electrode finger pitches different from the λ

/2 pitches, and a condition that at least one of the reflector electrodes having electrode finger pitches different from the λ

/2 pitches is disposed between two of the IDT electrodes is established,

the plurality of IDT electrodes includes a first, second and third IDT electrodes,

the plurality of reflector electrodes includes a first and second reflector electrodes,

the second IDT electrode is located on a first side of the first IDT electrode across the first reflector electrode,

the third IDT electrode is located on a second side of the first IDT electrode across the second reflector electrode,

the primary excitation region of the first IDT electrode is phase-shifted from the respective primary excitation regions of the second and third IDT electrodes by the certain amount in accordance with the desired passband frequency response, and

each of the first and second reflector electrodes has electrode finger pitches different from the λ

/2 pitches,

wherein the electrode finger pitches of at least one of the first and second reflector electrodes differ from one another and increase stepwise.

8. A longitudinally coupled surface acoustic wave filter comprising:

a piezoelectric substrate; and

a plurality of interdigital transducer electrodes (IDT electrodes) and a plurality of reflector electrodes disposed on the piezoelectric substrate,

wherein each of the IDT electrodes is an interdigital electrode including a plurality of opposed electrode fingers,

wherein the IDT electrodes and the reflector electrodes are arranged in close relation along a propagation direction of a surface acoustic wave,

wherein each of the IDT electrodes includes a primary excitation region having λ

/2 electrode finger pitches, where λ

is a wavelength of the surface acoustic wave,

wherein the primary excitation region of at least one of the IDT electrodes is phase-shifted from the primary excitation region of another IDT electrode by a certain amount in accordance with a desired passband frequency response, and

wherein at least one of a condition that at least one of the IDT electrodes includes, on a side thereof adjacent to another IDT electrode, a secondary excitation region having electrode finger pitches different from the λ

/2 pitches, and a condition that at least one of the reflector electrodes having electrode finger pitches different from the λ

/2 pitches is disposed between two of the IDT electrodes is established,

wherein;

the plurality of IDT electrodes includes at least five IDT electrodes,

the plurality of reflector electrodes includes at least four reflector electrodes each disposed between two of the IDT electrodes,

the primary excitation region of one of the IDT electrodes is phase-shifted from the primary excitation region of another of the IDT electrode by the certain amount in accordance with the desired passband frequency response, and

at least one of the reflector electrodes has electrode finger pitches different from the λ

/2 pitches.

9. The surface acoustic wave filter according to claim 8, wherein the electrode finger pitches of the at least one reflector electrode include two or more different kinds of electrode finger pitches.

10. The surface acoustic wave filter according to claim 8, wherein the electrode finger pitches of the at least one reflector electrode differ from one another and increase stepwise.