Longitudinally coupled surface acoustic wave resonator filter having different distances between transducers

• US 5,874,868 A
• Filed: 12/27/1996
• Issued: 02/23/1999
• Est. Priority Date: 12/28/1995
• Status: Expired due to Term

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Shimoe, Kazunobu
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Summons, Barbara
• Application Number:
  US08/775,012
• Time in Patent Office: 788 Days
• Field of Search: 310/313 B, 310/313 R, 310/313 C, 310/313 D, 333/193-196
• US Class Current: 333/193
• CPC Class Codes: H03H 9/6436 having one acoustic track only
• CPC Class Codes: H03H 9/6466 each track containing more than two transducers
• CPC Class Codes: H03H 9/6473 the electrodes being electrically interconnected

Abstract

A longitudinal coupling type SAW resonator filter achieves improved selectivity without increasing the insertion loss and is constructed so as to be more easily mass-produced. The longitudinal coupling type SAW resonator filter has a piezoelectric substrate and first, second and third sets of interdigital electrodes each including a pair of comb electrodes disposed on the piezoelectric substrate. A pair of reflectors are located on the opposite sides in the surface wave propagation direction of the area in which the first to third sets of interdigital electrodes are disposed. The distance between the centers of adjacent electrode fingers of the first and second sets of interdigital electrode and the distance between the centers of adjacent electrode fingers of the first and third sets of interdigital electrode are set to different values.

Claims

1. A longitudinally coupled surface acoustic wave resonator filter comprising:

a substrate;

first, second and third interdigital transducers disposed on a surface of said substrate;

said second and third interdigital transducers being located on opposite sides of said first interdigital transducer in a direction of propagation of surface waves excited and received by said first interdigital transducer;

first and second reflectors located on said substrate at opposite ends of an area in which said first, second and third interdigital transducers are provided;

each of said first, second and third interdigital transducers including a pair of comb electrodes each having at least one electrode finger; and

a distance L₁ between centers of the at least one electrode finger of said first interdigital transducer and the at least one electrode finger of said second interdigital transducer located adjacent to each other and a distance L₂ between centers of the at least one electrode finger of said first interdigital transducer and the at least one electrode finger of said third interdigital transducer located adjacent to each other being set to different values;

wherein

each of said first and second reflectors has a plurality of electrode fingers arranged substantially perpendicularly to the surface wave propagation direction, a wavelength of surface waves determined by an electrode pitch of the reflectors is λ and

said distance L₁ satisfies an inequality (1);

space="preserve" listing-type="equation">0+nλ

≦

L.sub.1 ≦

λ

/2+nλ

(1)

space="preserve" listing-type="equation">(n;

an integer)

said distance L₂ satisfies an inequality (2);

space="preserve" listing-type="equation">λ

/2+mλ

≦

L.sub.2 ≦

(m+1)λ

(2)

space="preserve" listing-type="equation">(m;

an integer)

said distance L₁ and L₂ satisfy an inequality (3);

space="preserve" listing-type="equation">L.sub.1 ≠

L.sub.2 -λ

/2+kλ

(3)

space="preserve" listing-type="equation">(k;

an integer).

2. A longitudinally coupled surface acoustic wave resonator filter according to claim 1, wherein said substrate comprises one of a piezoelectric substrate and a substrate including a piezoelectric thin film disposed thereon.

3. A double mode filter comprising:

a longitudinally coupled surface acoustic wave resonator filter including first, second and third interdigital transducers disposed on a surface of said substrate, said second and third interdigital transducers being located on opposite sides of said first interdigital transducer in a direction of propagation of surface waves excited and received by said first interdigital transducer, first and second reflectors located on said substrate at opposite ends of an area in which said first, second and third interdigital transducers are provided, each of said first, second and third interdigital transducers including a pair of comb electrodes each having at least one electrode finger, and a distance L₁ between centers of the at least one electrode finger of said first of interdigital transducer and the at least one electrode finger of said second interdigital transducer located adjacent to each other and a distance L₂ between centers of the at least one electrode finger of said first interdigital transducer and the at least one electrode finger of said third interdigital transducer located adjacent to each other being set to different values;

wherein each of said first and second reflectors has a plurality of electrode fingers arranged substantially perpendicularly to the surface wave propagation direction, a wavelength of surface waves determined by an electrode pitch of the reflectors is λ and

said distance L₁ satisfies a relationship (1);

space="preserve" listing-type="equation">0+nλ

≦

L.sub.1 ≦

λ

/2+nλ

(1)

space="preserve" listing-type="equation">(for any value of n where n is an integer)

said distance L₂ satisfies a relationship (2);

space="preserve" listing-type="equation">λ

/2+mλ

≦

L.sub.2 ≦

(m+1)λ

(2)

space="preserve" listing-type="equation">(for any value of m where m is an integer)

said distances L₁ and L₂ do not satisfy a relationship (3);

space="preserve" listing-type="equation">L.sub.1 =L.sub.2 -λ

/2+kλ

(3)

space="preserve" listing-type="equation">(for all values of k where k is any integer)

such that two resonant modes are defined in the double mode filter;

at least one of a longitudinally coupled surface acoustic wave resonator filter, a transversely coupled surface acoustic wave resonator filter and a trap filter including a surface acoustic wave resonator disposed on the substrate and electrically connected to said longitudinally coupled surface acoustic wave resonator filter.

4. A multiple-IDT longitudinally coupled surface acoustic wave resonator filter comprising:

a substrate;

first to Xth (X;

an integer equal to or larger than

     4) interdigital transducers disposed on a surface of said substrate;

said second to Xth interdigital transducers being arranged to extend along a direction of propagation of surface waves excited and received by said first interdigital transducer;

first and second reflectors located on said substrate at opposite sides of an area in which said first to Xth interdigital transducers are provided; and

each of said interdigital transducers including a pair of comb electrodes each having at least one electrode finger;

wherein

distances between adjacent-end electrode fingers of adjacent pairs of said interdigital transducers are L₁, L₂, . . . L_X-1 and the distances satisfy equations (4) and (5);

space="preserve" listing-type="equation">L.sub.S =L.sub.1 =L.sub.3 =L.sub.5 . . . (4)

space="preserve" listing-type="equation">L.sub.A =L.sub.2 =L.sub.4 =L.sub.6 . . . (5)

wherein, a wavelength of surface waves determined by an electrode finger pitch of said reflectors is λ and

said distances L_S and L_A satisfy inequalities (6) and (7);

space="preserve" listing-type="equation">0+nλ

≦

L.sub.S ≦

λ

/2+nλ

(6)

space="preserve" listing-type="equation">(n;

integer)

space="preserve" listing-type="equation">λ

/2+mλ

≦

L.sub.A ≦

(m+1)λ

(7)

space="preserve" listing-type="equation">(m;

integer)

or inequalities (8) and (9);

space="preserve" listing-type="equation">λ

/2+nλ

≦

L.sub.S ≦

(n+1)λ

(8)

space="preserve" listing-type="equation">(n;

integer)

space="preserve" listing-type="equation">0+mλ

≦

L.sub.A ≦

λ

/2+mλ

(9)

space="preserve" listing-type="equation">(m;

integer),

and

the distances L_S and L_A satisfy an inequality (10);

space="preserve" listing-type="equation">L.sub.S ≠

L.sub.A -λ

/2+kλ

(10)

space="preserve" listing-type="equation">(k;

integer).

5.

5. An electronic component comprising:

a substrate;

a plurality of longitudinally coupled surface acoustic wave resonator filters located on said substrate and connected in series to each other, each of said plurality longitudinally coupled surface acoustic wave filters including;

first, second and third interdigital transducers disposed on a surface of said substrate;

said second and third interdigital transducers being located on opposite sides of said first interdigital transducer in a direction of propagation of surface waves excited and received by said first interdigital transducer;

first and second reflectors located on said substrate at opposite ends of an area in which said first, second and third interdigital transducers are provided;

each of said first, second and third interdigital transducers including a pair of comb electrodes each having at least one electrode finger; and

a distance L₁ between centers of the at least one electrode finger of said first interdigital transducer and the at least one electrode finger of said second interdigital transducer located adjacent to each other and a distance L₂ between centers of the at least one electrode finger of said first interdigital transducer and the at least one electrode finger of said third interdigital transducer located adjacent to each other being set to different values;

wherein

each of said first and second reflectors has a plurality of electrode fingers arranged substantially perpendicularly to the surface wave propagation direction, a wavelength of surface waves determined by an electrode pitch of the reflectors is λ and

said distance L₁ satisfies an inequality (1);

space="preserve" listing-type="equation">0+nλ

≦

L.sub.1 ≦

λ

/2+nλ

(1)

space="preserve" listing-type="equation">(n;

an integer)

said distance L₂ satisfies an inequality (2);

space="preserve" listing-type="equation">λ

/2+mλ

≦

L.sub.2 ≦

(m+1)λ

(2)

space="preserve" listing-type="equation">(m;

an integer)

said distance L₁ and L₂ satisfy an inequality (3);

space="preserve" listing-type="equation">L.sub.1 ≠

L.sub.2 -λ

/2+kλ

(3)

space="preserve" listing-type="equation">(k;

an integer).

6. A surface acoustic wave resonator filter device comprising:

a longitudinally coupled surface acoustic wave resonator filter including first, second and third interdigital transducers disposed on a surface of said substrate, said second and third interdigital transducers being located on opposite sides of said first interdigital transducer in a direction of propagation of surface waves excited and received by said first interdigital transducer, first and second reflectors located on said substrate at opposite ends of an area in which said first, second and third interdigital transducers are provided, each of said first, second and third interdigital transducers including a pair of comb electrodes each having at least one electrode finger and a distance L₁ between centers of the at least one electrode finger of said first interdigital transducer and the at least one electrode finger of said second interdigital transducer located adjacent to each other and a distance L₂ between centers of the at least one electrode finger of said first interdigital transducer and the at least one electrode finger of said third interdigital transducer located adjacent to each other being set to different values;

wherein each of said first and second reflectors has a plurality of electrode fingers arranged substantially perpendicularly to the surface wave propagation direction, a wavelength of surface waves determined by an electrode pitch of the reflectors is λ and

said distance L₁ satisfies an inequality (1);

space="preserve" listing-type="equation">0+nλ

≦

L.sub.1 ≦

λ

/2+nλ

(1)

space="preserve" listing-type="equation">(n;

an integer)

said distance L₂ satisfies an inequality (2);

space="preserve" listing-type="equation">λ

/2+mλ

≦

L.sub.2 ≦

(m+1)λ

(2)

space="preserve" listing-type="equation">(m;

an integer)

said distance L₁ and L₂ satisfy an inequality (3);

space="preserve" listing-type="equation">L.sub.1 ≠

L.sub.2 -λ

/2+kλ

(3)

space="preserve" listing-type="equation">(k;

an integer);

and

at least one of a longitudinally coupled surface acoustic wave resonator filter, a transversely coupled surface acoustic wave resonator filter and a trap filter including a surface acoustic wave resonator disposed on the substrate and electrically connected to said longitudinally coupled surface acoustic wave resonator filter.

7. A double mode filter comprising

a substrate;

first, second and third interdigital transducers disposed on a surface of said substrate;

said second and third interdigital transducers being located on opposite sides of said first interdigital transducer in a direction of propagation of surface waves excited and received by said first interdigital transducer;

first and second reflectors located on said substrate at opposite ends of an area in which said first, second and third interdigital transducers are provided;

each of said first, second and third interdigital transducers including a pair of comb electrodes each having at least one electrode finger; and

a distance L₁ between centers of the at least one electrode finger of said first interdigital transducer and the at least one electrode finger of said second interdigital transducer located adjacent to each other and a distance L₂ between centers of the at least one electrode finger of said first interdigital transducer and the at least one electrode finger of said third interdigital transducer located adjacent to each other being set to different values;

wherein

each of said first and second reflectors has a plurality of electrode fingers arranged substantially perpendicularly to the surface wave propagation direction, a wavelength of surface waves determined by an electrode pitch of the reflectors is λ and

said distance L₁ satisfies a relationship (1);

space="preserve" listing-type="equation">0+nλ

≦

L.sub.1 ≦

λ

/2+nλ

(1)

space="preserve" listing-type="equation">(for all values of n where n is any integer)

said distance L₂ satisfies a relationship (2);

space="preserve" listing-type="equation">λ

/2+mλ

≦

L.sub.2 ≦

(m+1)λ

(2)

space="preserve" listing-type="equation">(for all values of m where m is any integer)

said distances L₁ and L₂ do not satisfy a relationship (3);

space="preserve" listing-type="equation">L.sub.1 =L.sub.2 -λ

/2+kλ

(3)

space="preserve" listing-type="equation">(for all values of k where k is any integer)

such that two resonant modes are defined in the double mode filter.

8. The double mode filter according to claim 7, wherein said substrate comprises one of a piezoelectric substrate and a substrate including a piezoelectric thin film disposed thereon.

9. A double mode filter comprising:

a substrate;

first to Xth (X is any integer equal to or larger than

     4) interdigital transducers disposed on a surface of said substrate;

said second to Xth interdigital transducers being arranged to extend along a direction of propagation of surface waves excited and received by said first interdigital transducer;

first and second reflectors located on said substrate at opposite sides of an area in which said first to Xth interdigital transducers are provided; and

each of said interdigital transducers including a pair of comb electrodes each having at least one electrode finger;

wherein

distances between adjacent end electrode fingers of adjacent pairs of said interdigital transducers are L₁, L₂, . . . L_x-1 and the distances satisfy equations (4) and (5);

space="preserve" listing-type="equation">L.sub.S =L.sub.1 =L.sub.3 =L.sub.5 . . . (4)

space="preserve" listing-type="equation">L.sub.A =L.sub.2 =L.sub.4 =L.sub.6 . . . (5)

wherein a wavelength of surface waves determined by an electrode finger pitch of said reflectors is λ and

said distances L_s and L_A satisfy relationships (6) and (7);

space="preserve" listing-type="equation">0+nλ

≦

L.sub.S ≦

λ

/2+nλ

(6)

space="preserve" listing-type="equation">(for any value of n where n is an integer)

space="preserve" listing-type="equation">λ

/2+mλ

≦

L.sub.A ≦

(m+1)λ

(7)

space="preserve" listing-type="equation">(for any value of m where m is an integer)

or relationships (8) and (9);

space="preserve" listing-type="equation">0+nλ

≦

L.sub.S ≦

(n+1)λ

(8)

space="preserve" listing-type="equation">(for any value of n where n is an integer)

space="preserve" listing-type="equation">0+mλ

≦

L.sub.A ≦

λ

/2+mλ

(9)

space="preserve" listing-type="equation">(for any value of m where m is an integer)

and said distances L₁ and L₂ do not satisfy a relationship (10);

space="preserve" listing-type="equation">L.sub.S =L.sub.A -λ

/2+kλ

(10)

space="preserve" listing-type="equation">(for all values of k where k is any integer)

such that two resonant modes are defined in the double mode filter.

10. A double mode filter comprising:

a substrate;

a plurality of longitudinally coupled surface acoustic wave resonator filters located on said substrate and connected in series to each other, each of said plurality of longitudinally coupled surface acoustic wave filters including;

first, second and third interdigital transducers disposed on a surface of said substrate;

said second and third interdigital transducers being located on opposite sides of said first interdigital transducer in a direction of propagation of surface waves excited and received by said first interdigital transducer;

first and second reflectors located on said substrate at opposite ends of an area in which said first, second and third interdigital transducers are provided;

each of said first, second and third interdigital transducers including a pair of comb electrodes each having at least one electrode finger; and

a distance L₁ between centers of the at least one electrode finger of said first interdigital transducer and the at least one electrode finger of said second interdigital transducer located adjacent to each other and a distance L₂ between centers of the at least one electrode finger of said first interdigital transducer and the at least one electrode finger of said third interdigital transducer located adjacent to each other being set to different values;

wherein

each of said first and second reflectors has a plurality of electrode fingers arranged substantially perpendicularly to the surface wave propagation direction, a wavelength of surface waves determined by an electrode pitch of the reflectors is λ and

said distance L₁ satisfies a relationship (1);

space="preserve" listing-type="equation">0+nλ

≦

L.sub.1 ≦

λ

/2+nλ

(1)

space="preserve" listing-type="equation">(for any value of n where n is an integer)

said distance L₂ satisfies a relationship (2);

space="preserve" listing-type="equation">λ

/2+mλ

≦

L.sub.2 ≦

(m+1)λ

(2)

space="preserve" listing-type="equation">(for any value of m where m is an integer)

said distances L₁ and L₂ do not satisfy a relationship (3);

space="preserve" listing-type="equation">L.sub.1 =L.sub.2 -λ

/2+kλ

(3)

space="preserve" listing-type="equation">(for all values of k where k is any integer)

such that two resonant modes are defined in the double mode filter.