JP2000031785A - Surface acoustic wave resonator filter - Google Patents

Abstract

(57) Abstract: A broadband, low-impedance, multipole two-dimensional mode-coupled SAW filter is obtained on the same substrate. SOLUTION: A plurality of IDT electrodes, grating electrodes, and grating reflectors are arranged on a piezoelectric substrate to excite three longitudinal resonance modes and three transverse resonance modes, and acoustically couple these resonance modes. Thus, nine filters are obtained to form a filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave resonator filter, and more particularly, to a surface acoustic wave resonator filter having a two-dimensional mode-coupled SAW filter with a wider band.

[0002]

2. Description of the Related Art In recent years, SAW devices have been widely used in the field of communications, and have excellent characteristics such as high performance, small size, and mass productivity, and thus are widely used especially in mobile phones and the like, and play a part in their spread. . FIG.
7, acoustically couples the longitudinal resonance mode in the longitudinal direction, which is the propagation direction of the surface acoustic wave, with the transverse resonance mode in the transverse direction, which is orthogonal to the SAW filter. FIG. 5 is a plan view showing a configuration of a resonator type multi-mode SAW filter. The IDT electrode 21 and the grating electrode 22 are arranged close to each other along the propagation direction of the surface acoustic wave on the piezoelectric substrate 20, and the grating reflectors 23a and 23b are arranged on both sides of the IDT electrode 21 and the grating electrode 22 to form the resonator α. Further, a resonator β having an IDT electrode 24, a grating 25, and grating reflectors 26a and 26b, which has the same configuration as the resonator α but replaces the positional relationship between the IDT electrode 21 and the grating electrode 22, A two-dimensional mode-coupled SAW filter is formed close to and adjacent to the resonator α.

FIGS. 4 (b) and 4 (c) show transverse resonance modes excited by the resonators α and β. FIG. 4 (b) shows a symmetric resonance mode (transverse first resonance mode) and FIG. c) is an obliquely symmetric resonance mode (lateral secondary resonance mode). FIGS. 4D and 4E show resonance modes in the vertical direction.
(D) is a symmetric resonance mode (vertical primary resonance mode), and (e) is an oblique symmetric resonance mode (vertical secondary resonance mode). The two-dimensional mode-coupling type SAW filter has two resonance modes, FIGS. 4B and 4C, which are excited in the horizontal direction, and two resonance modes, FIGS. 4D and 4E which are excited in the vertical direction. Acoustically couple the four resonance modes F (i,
j) (i = 1 to 2, j = 1 to 2) are vigorously excited.
(Here, F (i, j) indicates the resonance mode and the resonance frequency of the mode at the same time.) Here, the symbols i and j indicate the order of the horizontal and vertical resonance modes, respectively. Then, the frequency arrangement of the transverse first-order system, that is, the symmetric mode system, becomes F (1,2) <F (1,1), and the modes F (1,1) and F (1,2) have opposite phases Become a relationship. In addition, the frequency arrangement of the transverse quadratic system, that is, the oblique symmetric mode system, becomes F (2,2) <F (2,1), and similarly, the modes F (2,1) and F (2,2) are inversed. It becomes a phase relationship.

Here, a method of extracting the input / output IDT electrodes is set so that the symmetric mode system (lateral primary mode system) and the oblique symmetric mode system (lateral secondary mode system) have opposite phases. For example, in the example of FIG. 4, the IDT electrode 21 is realized by inputting a comb-shaped electrode on the lower side in the drawing and outputting the IDT electrode 24 by outputting a comb-shaped electrode on the upper side of the drawing. Further, as shown in FIG. 5, when the frequency relationship between the two modes is set so that F (1,1) ≒ F (2,2), a two-dimensional mode-coupled SAW filter can be configured. FIG. 5 shows the order of the transverse mode on the vertical axis,
FIG. 3 is a diagram showing the order of the longitudinal mode on the horizontal axis and the frequency arrangement and phase relationship of each resonance mode. Here, it is assumed that a white circle represents a phase difference of 180 degrees when a white circle represents a zero phase. The feature of the two-dimensional mode coupling type SAW filter is that it is a vertical coupling type SAW filter or a horizontal coupling type SAW filter.
The point is that a SAW filter having a wider band than a filter can be configured.

[0005]

However, in the two-dimensional mode-coupling type SAW filter described above, when a wider band is to be achieved, as a result of increasing the resonance frequency interval of each mode, the input / output impedance of the filter is reduced to the required input / output. There is a problem that the impedance becomes too large. Further, there is a problem that the attenuation gradient is insufficient for only one section of the three-pole filter (filter order) with respect to the required filter attenuation standard. The present invention has been made to solve the above problem, and has as its object to provide a two-dimensional mode-coupled SAW filter having a sufficient attenuation gradient over a wide band.

[0006]

According to a first aspect of the present invention, there is provided a surface acoustic wave resonator filter according to the present invention, wherein a plurality of surface acoustic wave resonators are provided on a piezoelectric substrate. Are arranged close so that the propagation directions of
A filter is formed using N × M (N × M ≧ 6) resonance modes obtained by acoustically coupling (N ≧ 2) transverse mode resonances and M (M ≧ 2) longitudinal mode resonances. It is a surface acoustic wave filter characterized in that it is configured. The invention according to claim 2 is characterized in that three transverse mode resonances from the first transverse mode to the third transverse mode and three longitudinal mode resonances from the first longitudinal mode to the third longitudinal mode are used. A surface acoustic wave filter according to claim 1. According to a third aspect of the present invention, when the resonance mode obtained by acoustic coupling of the i-th transverse mode and the j-th longitudinal mode is F (i, j),
(1, 2) and F (2, 3) have the same frequency,
(1,1), F (2,2) and F (3,3) have the same frequency, and F (2,1) and F (3,2) have the same frequency. 3. The method according to claim 2, wherein
It is a surface acoustic wave filter described. According to a fourth aspect of the present invention, at least one of the surface acoustic wave resonators is replaced with a grating electrode.
It is a surface acoustic wave filter described.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1 is a plan view showing a configuration of a surface acoustic wave resonator filter according to the present invention, in which an IDT electrode 2 and grating electrodes 3 and 4 are closely arranged on a main surface of a piezoelectric substrate 1 along a propagation direction of a surface wave. Then, grating reflectors 5a and 5b are arranged on both sides thereof to form a resonator A. Further, a grating electrode B is juxtaposed in parallel with the resonator A, and the configuration is the same as that of the resonator A in parallel with the grating electrode B.
A two-dimensionally arranged surface acoustic wave resonator filter in which a resonator C composed of an IDT electrode 6, grating electrodes 7, 8 and reflectors 9a, 9b in which the positional relationship between the electrode 2 and the grating electrode 4 is replaced is arranged in close proximity. To form

In the configuration of the IDT electrode and the grating electrode shown in FIG. 1, in the longitudinal direction (the propagation direction of the surface wave), FIG.
The three resonance modes shown in (b), (c), and (d), that is, the first-order, second-order, and third-order resonance modes are strongly excited, and the horizontal direction (the direction orthogonal to the propagation direction of the surface wave) ) Also includes the three horizontal primary, secondary, and horizontal shown in FIGS. 1 (e), (f), and (g).
The tertiary resonance mode is strongly excited. These FIG. 1 (b)
As a result of the acoustic coupling of the modes (g) to (g), nine resonance modes F (i, j) (i = 1 to 3, j = 1 to 3) are excited.

The above surface acoustic wave resonator filter is one type of a two-dimensional mode-coupling type SAW filter. The resonance mode and the frequency relationship will be described. F (1,1), F (1,
2), F (1,3) is strongly excited, and its frequency arrangement is F (1,3) <F (1,2) <F (1,1), and mode F (1,1) is the mode Although the phase is opposite to F (1,2), the mode is the same as mode F (1,3).

[0010] Next, in the transverse secondary system, that is, in the oblique symmetric mode system, 3
Modes F (2,1), F (2,2), F (2,3)
Is strongly excited, and the frequency arrangement is F (2,3) <F (2,2) <F (2,1), and each mode is sequentially from a higher frequency to a lower frequency.
The phase will be inverted by 180 degrees. Further, in a transverse third-order system, that is, in a symmetric mode system, three modes F (3, 1),
F (3,2) and F (3,3) are strongly excited, and their frequency arrangement is F (3,3) <F (3,2) <F (3,1). In the mode, the phase is sequentially inverted by 180 degrees from the higher frequency to the lower frequency.

The magnitude of the coupling in the transverse mode system is determined by the intersection width w _i
It is well known that it depends on the gap width g _i (i = 1, 2) between the IDT electrodes (i = 1, 2, 3 in FIG. 1). That is, when extending the resonance frequency interval, w _i ,
a g _i, etc. may be reduced. It is also well known that the magnitude of coupling in a vertical coupling system depends on the number of IDT electrodes, the ratio of the number of IDT electrodes to the number of grating electrodes, the ratio of the pitch between IDT electrodes and grating electrodes, and the like.

FIG. 2A shows the frequency arrangement F (i, j) of each mode and its phase relationship using the means for controlling the degree of coupling between the horizontal coupling mode and the vertical coupling mode. Adjust to That is, F (3,2) ≒ F (2,1) F (3,3) ≒ F (2,2) ≒ F (1,1) F (2,3) ≒ F (1,2) The frequency is adjusted as described above, and the phase of each mode is set such that the white circle (○) in FIG. For example, the input and output lead terminals may be set as shown in FIG. 1, and a five-pole two-dimensional mode-coupled SAW filter can be configured. When the input / output terminals (IN, OUT) of the surface acoustic wave resonator filter are terminated with low resistance, transmission characteristics having five resonance characteristics are observed as shown in FIG. You can see that. If this filter is appropriately terminated, a five-pole surface acoustic wave resonator filter having a flat pass band and steep attenuation characteristics can be obtained. Since the filter order is higher, it is possible to realize a SAW filter having a wider band than a conventional three-pole two-dimensional mode coupling type SAW filter and having a steep attenuation characteristic.

3 (a) and 3 (b) show another embodiment according to the present invention. FIG. 3 (a) shows two resonance modes obtained by two-dimensionally acoustically coupling two transverse modes and three longitudinal modes. And the frequencies of the horizontal mode and the vertical mode are adjusted so that F (1,1) ≒ F (2,2) F (1,2) ≒ F (2,3).
This is a configuration of a pole two-dimensional mode coupling SAW filter. FIG. 3B shows another embodiment according to the present invention, in which three transverse modes and two longitudinal modes are two-dimensionally acoustically coupled to excite six resonance modes, and F (2, 1 ) ≒ F (3,2) By adjusting the frequency of the horizontal mode and the vertical mode so that F (1,1) ≒ F (3,2), 4
This is a configuration of a pole two-dimensional mode coupling SAW filter.

Although the surface acoustic wave resonator filter shown in FIG. 1 is an example of a balanced two-dimensional mode coupling type SAW filter, the surface acoustic wave resonator filter according to the present invention has an unbalanced two-dimensional mode coupling type. Needless to say, the present invention can be applied to a type SAW filter.

[0015]

According to the present invention, as described above, a multi-pole two-dimensional mode-coupling SA on a piezoelectric substrate is provided.
Since a W filter can be formed, the order of the filter is increased and the increase in impedance is suppressed,
A steep but low impedance SAW filter can be realized. When the filter according to the present invention is used in a mobile phone or the like that requires miniaturization, there is a great advantage that the size is reduced while the performance is improved.

[Brief description of the drawings]

FIG. 1 (a) is a plan view showing an electrode pattern of a surface acoustic wave resonator filter according to the present invention, (b), (c),
(D) shows displacements in the first, second, and third longitudinal modes, and (e), (f), and (g) show first and second transverse resonances, respectively.
It is a figure which shows the displacement of a 3rd order mode.

FIG. 2A is a diagram showing a horizontal-longitudinal resonance mode frequency arrangement and its phase relationship, and FIG. 2B is a transmission characteristic in the case of terminating with a low resistance.

FIGS. 3A and 3B are diagrams showing a frequency arrangement and a phase relationship of a second-order to third-order surface acoustic wave resonator filter according to another embodiment of the present invention, and FIG. It is a figure which shows the frequency arrangement | sequence of a longitudinal secondary surface acoustic wave resonator filter, and its phase relationship.

4A is a diagram showing an electrode pattern of a conventional two-dimensional mode-coupling type SAW filter, and FIGS. 4B and 4C are diagrams showing displacements of transverse resonance primary and secondary modes; (E) is a diagram showing the displacement of the longitudinal resonance primary and secondary modes.

FIG. 5 is a diagram showing a resonance frequency arrangement and a phase relationship of a two-dimensional mode coupling type SAW filter.

[Explanation of symbols]

1. Piezoelectric substrate 6. IDT electrodes 4, 7, 8 Grating electrodes 5a, 5b, 9a, 9b Grating reflectors A, B, C Resonator IN, OUT I / O terminal F ( i, j)... resonance mode and its frequency (i = 1 to
3; j = 1 to 3, i represents the order of the horizontal mode, and j represents the order of the vertical mode.) White circles (）), black circles (●)...

Claims (4)

[Claims] 1. A plurality of surface acoustic wave resonators are arranged close to each other on a piezoelectric substrate such that propagation directions of surface acoustic waves are parallel to each other.
N × M obtained by acoustically coupling N (N ≧ 2) transverse mode resonances and M (M ≧ 2) longitudinal mode resonances
A surface acoustic wave filter comprising a filter using (N × M ≧ 6) resonance modes. 2. The three modes from the first-order transverse mode to the third-order transverse mode.
2. A surface acoustic wave filter according to claim 1, wherein two transverse mode resonances and three longitudinal mode resonances from a first-order longitudinal mode to a third-order longitudinal mode are used. 3. When a resonance mode obtained by acoustic coupling between an i-th transverse mode and a j-th longitudinal mode is F (i, j),
F (1,2) and F (2,3) have the same frequency,
F (1,1), F (2,2) and F (3,3) have the same frequency, and F (2,1) and F (3,2) have the same frequency. The surface acoustic wave filter according to claim 2, wherein: 4. The surface acoustic wave filter according to claim 1, wherein at least one of the surface acoustic wave resonators is replaced with a grating electrode.