Resonator filter with improved adjacent channel selectivity

• US 6,894,588 B2
• Filed: 02/14/2003
• Issued: 05/17/2005
• Est. Priority Date: 02/15/2002
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Epcos AG (TDK Corporation)
• Inventors: Detlefsen, Andreas
• Primary Examiner(s): Summons, Barbara
• Application Number:
  US10/366,873
• Publication Number:
  US 20030231083A1
• Time in Patent Office: 823 Days
• Field of Search: 333193-196, 310/313.B, 310/313.D
• US Class Current: 333/195
• CPC Class Codes: H03H 9/643 the transfer characteristic being determined by reflective or coupling array characteristics
• CPC Class Codes: H03H 9/6436 having one acoustic track only
• CPC Class Codes: H03H 9/6469 via two connecting electrodes
• CPC Class Codes: H03H 9/6483 Ladder SAW filters

Abstract

For improving the adjacent channel selectivity of a resonator filter, reflectors of resonators are differently designed so that the minimums of the reflection functions of different reflectors of a resonator are shifted relative to one another and preferably compensate with the corresponding maximum of the respectively other reflection function. This reduces noise spikes at the low-frequency side of the pass-band of corresponding resonator filters and, thus, improves the adjacent channel selectivity.

Claims

1. A resonator filter for acoustic surface waves or surface-proximate waves, comprising:

a whole positive number n of acoustic resonators fashioned on a piezoelectric substrate, each respectively comprising at least one interdigital transducer; and

a first and a second reflector between which the at least one interdigital transducer is arranged, the reflectors being respectively allocated to at least one of the n resonators and that respectively are constructed to exhibit a frequency-dependent reflection behavior and to provide a reflection function comprising at least one minimum;

wherein the first and the second reflector are fashioned differently so that the frequency position of the minimums of the two reflection functions of the first and second reflector are shifted relative to one another; and

wherein the minimums of the reflection functions of the first and second reflector are shifted relative to one another such that a minimum of the first reflection function has approximately the same frequency position as a maximum of the second reflection function.

2. The resonator filter according to claim 1, further comprising:

a first acoustic track and a second acoustic track, a first acoustic resonator being provided in the first acoustic track, and a second acoustic resonator being provided in the second acoustic track, the first resonator and the second resonator being connected to one another;

the first and second reflectors being arranged in a same track.

3. The resonator filter according to claim 1, wherein the resonator filter is fashioned as a single-track or multi-track dual-mode SAW (DMS) filter.

4. The resonator filter according to claim 1, wherein a spacing of respectively two neighboring centers of reflector strips varies over a length of the reflectors measured in a wave propagation direction.

5. The resonator filter according to claim 4, wherein specific values for the spacing of two neighboring reflector strip centers follow corresponding function values of a periodically sampled, steady function viewed over the length of the resonators.

6. The resonator filter according to claim 1, wherein a width of reflector strips varies over a length of the reflectors measured in a wave propagation direction.

7. The resonator filter according to claim 1, wherein, when comprising one-port resonators, an interdigital transducer is arranged at each one-port resonator between a first and a second reflector, and frequency positions of the minimums of the reflection functions of the first and second reflector are shifted relative to one another at at least one resonator.

8. The resonator filter according to claim 1, wherein at least one of the reflectors has reflector stripes and is divided into two or more segments that differ on the basis of at least one of a plurality and spacing of centers of the reflector stripes.

9. The resonator filter according to claim 8, wherein the segments of the at least one reflector are arranged parallel to one another and thus respectively form a sub-aperture of the resonator, the sum of the sub-aperture widths allocated to the segments corresponds to at least an overall aperture of the resonator.

10. The resonator filter according to claim 8, wherein the segments are arranged following one another in a wave propagation direction.

11. The resonator filter according to claim 1, wherein specific values for a width of at least one of electrode fingers residing at an end and reflector stripes residing at at least one of the end and a center-to-center spacing of at least one of respectively two neighboring electrode fingers and reflector stripes in a region of the transition between two resonator structure elements follow corresponding function values of a steady function in the region of the transition as viewed over a length of the resonator, thereby avoiding discontinuities and hard transitions between neighboring resonator structure elements.

12. A resonator filter for acoustic surface waves or surface-proximate waves, comprising:

a whole positive number n of acoustic resonators fashioned on a piezoelectric substrate, each respectively comprising at least one interdigital transducer; and

a first and a second reflector between which the at least one interdigital transducer is arranged, the reflectors being respectively allocated to at least one of the n resonators and that respectively are constructed to exhibit a frequency-dependent reflection behavior and to provide a reflection function comprising at least one minimum;

wherein the first and the second reflector are fashioned differently so that the frequency position of the minimums of the two reflection functions of the first and second reflector are shifted relative to one another;

wherein a width of reflector strips varies over a length of the reflectors measured in a wave propagation direction; and

wherein specific values for the width of reflector strips follow corresponding function values of a periodically sampled, steady function viewed over the length of the resonators.

13. The resonator filter according to claim 12, further comprising:

a first acoustic track and a second acoustic track, a first acoustic resonator being provided in the first acoustic track, and a second acoustic resonator being provided in the second acoustic track, the first resonator and the second resonator being connected to one another;

the first and second reflectors being arranged in a same track.

14. The resonator filter according to claim 12, wherein the resonator filter is fashioned as a single-track or multi-track dual-wave SAW (DMS) filter.

15. The resonator filter according to claim 12, wherein specific values for a width of at least one of electrode fingers residing at an end and reflector stripes residing at at least one of the end and a center-to-center spacing of at least one of respectively two neighboring electrode fingers and reflector stripes in a region of the transition between two resonator structure elements follow corresponding function values of a steady function in the region of the transition as viewed over a length of the resonator, thereby avoiding discontinuities and hard transitions between neighboring resonator structure elements.

16. A resonator filter for acoustic surface waves or surface-proximate waves, comprising:

a whole positive number n of acoustic resonators fashioned on a piezoelectric substrate, each respectively comprising at least one interdigital transducer; and

a first and a second reflector between which the at least one interdigital transducer is arranged, the reflectors being respectively allocated to at least one of the n resonators and that respectively are constructed to exhibit a frequency-dependent reflection behavior and to provide a reflection function comprising at least one minimum;

wherein the first and the second reflector are fashioned differently so that the frequency position of the minimums of the two reflection functions of the first and second reflector are shifted relative to one another; and

wherein at least one of a width of individual and a center-to-center spacing of two neighboring electrode fingers of at least one of the interdigital transducers and reflector stripes varies continuously transverse to a length of the resonator composed of interdigital transducers and reflectors.

17. The resonator filter according to claim 16, wherein the quantities of width and center-to-center spacing transverse to the length are fashioned in a linearly increasing manner.

18. The resonator filter according to claim 17, further comprising:

a first acoustic track and a second acoustic track, a first acoustic resonator being provided in the first acoustic track, and a second acoustic resonator being provided in the second acoustic track, the first resonator and the second resonator being connected to one another;

the first and second reflectors being arranged in a same track.

19. The resonator filter according to claim 17, wherein the resonator filter is fashioned as a single-track or multi-track dual-wave SAW (DMS) filter.

20. The resonator filter according to claim 17, wherein specific values for a width of at least one of electrode fingers residing at an end and reflector stripes residing at at least one of the end and a center-to-center spacing of at least one of respectively two neighboring electrode fingers and reflector stripes in a region of the transition between two resonator structure elements follow corresponding function values of a steady function in the region of the transition as viewed over a length of the resonator, thereby avoiding discontinuities and hard transitions between neighboring resonator structure elements.

21. The resonator filter according to claim 16, wherein the resonator filter is fashioned as a single-track or multi-track dual-wave SAW (DMS) filter.

22. The resonator filter according to claim 16, further comprising:

a first acoustic track and a second acoustic track, a first acoustic resonator being provided in the first acoustic track, and a second acoustic resonator being provided in the second acoustic track, the first resonator and the second resonator being connected to one another;

the first and second reflectors being arranged in a same track.

23. The resonator filter according to claim 16, wherein specific values for a width of at least one of electrode fingers residing at an end and reflector stripes residing at at least one of the end and a center-to-center spacing of at least one of respectively two neighboring electrode fingers and reflector stripes in a region of the transition between two resonator structure elements follow corresponding function values of a steady function in the region of the transition as viewed over a length of the resonator, thereby avoiding discontinuities and hard transitions between neighboring resonator structure elements.

24. A resonator filter for acoustic surface waves or surface-proximate waves, comprising:

a first reflector that is divided into two or more segments arranged parallel to a propagation direction of a surface wave;

a second reflector that is divided into two or more segments arranged parallel to a propagation direction of a surface wave; and

an interdigital transducer arranged between the first reflector and the second reflector;

wherein a first acoustic sub-track is formed by two of the segments and the interdigital transducer lying between them, these two segments differing within a sub-track with regard to a separation of a middle of their reflector stripes;

wherein a second acoustic sub-track is formed by two of the segments and the interdigital transducer lying between them, these two segments differing within a sub-track with regard to a separation of a middle of their reflector stripes; and

wherein the segments differ between the first acoustic sub-track and the second acoustic sub-track.

25. The resonator filter according to claim 24, further comprising:

a first acoustic track and a second acoustic track, a first acoustic resonator being provided in the first acoustic track, and a second acoustic resonator being provided in the second acoustic track, the first resonator and the second resonator being connected to one another;

the first and second reflectors being arranged in a same track.

26. The resonator filter according to claim 24, wherein the resonator filter is fashioned as a single-track or multi-track dual-wave SAW (DMS) filter.

27. The resonator filter according to claim 24, wherein specific values for a width of at least one of electrode fingers residing at an end and reflector stripes residing at at least one of the end and a center-to-center spacing of at least one of respectively two neighboring electrode fingers and reflector stripes in a region of the transition between two resonator structure elements follow corresponding function values of a steady function in the region of the transition as viewed over a length of the resonator, thereby avoiding discontinuities and hard transitions between neighboring resonator structure elements.