JP3395752B2 - Surface acoustic wave filter - Google Patents

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 filter used for wireless communication equipment and the like.

[0002]

2. Description of the Related Art In recent years, the amount of information transmitted has increased due to the development of the information communication field. Along with this, a surface acoustic wave filter having a relatively wide band and excellent phase linearity in the pass band is required. Conventionally, a transversal type surface acoustic wave filter is suitable as such a surface acoustic wave filter. ing.

A conventional transversal surface acoustic wave filter will be described below.

FIG. 15 is a diagram showing a conventional transversal surface acoustic wave filter. Reference numeral 1501 denotes a piezoelectric substrate. Input and output interdigital transducer electrodes (hereinafter referred to as IDT electrodes) are formed on the piezoelectric substrate 1501, and an input IDT electrode 1502 and an output IDT electrode 1503 are arranged with a predetermined distance. By doing so, a surface acoustic wave filter is constructed.

Input IDT electrode 1502 and output IDT
The electrode 1503 has an IEEE Ultrasonics symposium, 1989,
The unidirectional excitation electrodes 1504 and 1505 according to the prior art disclosed in pp.77-89 are used, and as a basic configuration, a quarter width of the wavelength λ of the surface acoustic wave propagating on the piezoelectric substrate 1501. The basic unit is made up of a total of three electrode fingers including one λ / 4 width electrode finger and two λ / 8 width electrode fingers.

These unidirectional excitation electrodes 1504, 15
In 05, since the center of reflection by the electrode fingers is asymmetrical to the center of excitation of the surface acoustic wave, the propagation of the surface acoustic wave is directional. At the unidirectional excitation electrode 1504, directionality is generated from the input IDT 1502 to the output IDT electrode 1503, and at the unidirectional excitation electrode 1505, the output IDT is output.
Directionality occurs in the direction from T1503 to the input IDT electrode 1502.

The input IDT electrode 1502 and the output IDT electrode 1503 have an IEEE Ultrasonics symposiu
m, 1973, pp.423-426, and the input IDT electrode 150 is thinned by the conventional technique.
2 and the output IDT electrode 1503 has a plurality of regions 1506 in which electrode fingers are thinned out.

In the conventional surface acoustic wave filter configured as described above, the bidirectional loss peculiar to the transversal type surface acoustic wave filter is reduced by the unidirectional excitation electrode. In addition, a filter characteristic with a wide band and a flat pass band is realized by applying thinning weighting.

[0009]

In recent years, as mobile terminals have been downsized, there has been a demand for downsizing of surface acoustic wave filters in the IF stage. However, in the above-described transversal surface acoustic wave filter, when a high selectivity required for CDMA or the like, that is, a steep attenuation amount near the pass band is to be obtained, the input and output IDT electrodes Requires sufficient weighting, the IDT electrode length becomes long, and there is a problem that miniaturization is difficult.

Therefore, it is an object of the present invention to provide a surface acoustic wave filter which is smaller and has excellent selectivity characteristics in a wide pass band.

[0011]

The present invention according to claim 1 comprises a piezoelectric substrate and at least two interdigital transducer electrodes on the piezoelectric substrate, wherein at least one of the interdigital transducer electrodes is unidirectional excitation. The structure includes an electrode and first and second non-excitation electrodes, and the one-wavelength basic cell of the first non-excitation electrode is the one-wavelength basic cell of the unidirectional excitation electrode and the propagation direction of the surface acoustic wave. And the same one-wavelength basic cell of the second non-excitation electrode is symmetrical to the one-wavelength basic cell of the unidirectional excitation electrode with respect to the propagation direction of surface acoustic waves. Surface acoustic wave filter
And the unidirectional excitation electrode has one wavelength basic cell of 4
The configuration has four electrode fingers, and the four electrode fingers are two.
Forming two electrode finger pairs, the two electrode finger pairs being adjacent to each other
The line width of the electrode fingers is different, and the line width (L
1) and the line width (L2) of the thick electrode (L2 / L)
1) is larger than 1, and the unidirectional excitation
The surface acoustic wave filter is characterized in that at the pole, the electrode finger pair satisfies (Equation 1) . (Equation 1) γ> α + β However, γ is a thin electrode finger and a thick electrode finger in the electrode finger pair.
The distance between them, α is the area where the IDT electrode is divided into half wavelength units.
Distance between the left edge of and the thin electrode finger, β is the half wavelength of the IDT electrode
The distance between the right edge of the area divided by the unit and the thick electrode finger
Show each.

[0012]

[0013]

According to a second aspect of the present invention, there is provided a piezoelectric substrate and at least two interdigital transducer electrodes on the piezoelectric substrate, wherein at least one of the interdigital transducer electrodes is a unidirectional excitation electrode and first and first interdigital transducer electrodes. In addition to the configuration including two non-excitation electrodes, the unidirectional excitation electrode has a configuration in which the one-wavelength basic cell has four electrode fingers, and the four electrode fingers form two electrode finger pairs. The two electrode finger pairs have different electrode finger line widths, and the line width ratio (L2 / L1) between the thin electrode finger line width (L1) and the thick electrode line width (L2) is greater than 1. In addition to the large configuration, the first and second non-excitation electrodes have a configuration in which the one-wavelength basic cell has four electrode fingers, and the four electrode fingers form two electrode finger pairs. Two electrode finger pairs are adjacent The electrode fingers have different line widths, and the line width ratio (Lr2 / Lr1) between the thin reflector electrode finger line width (Lr1) and the thick reflector electrode finger line width (Lr2) is greater than 1. elastic table 1 wavelength basic cell is an electrode structure of a left-right symmetrical with respect to the propagation direction of the wave basic cell and the surface acoustic wave of said second non excitation electrode of the first non-excitation electrode
A surface wave filter, comprising a unidirectional excitation electrode
It is a surface acoustic wave filter characterized in that a pair of pole fingers is configured to satisfy (Equation 1) . (Equation 1) γ> α + β However, γ is a thin electrode finger and a thick electrode finger in the electrode finger pair.
The distance between them, α is the area where the IDT electrode is divided into half wavelength units.
Distance between the left edge of and the thin electrode finger, β is the half wavelength of the IDT electrode
The distance between the right edge of the area divided by the unit and the thick electrode finger
Show each.

The present invention of claim 3, in claim 2 in which the line width ratio of the first and / or second non excitation electrode (Lr1 / Lr2) is characterized by having regions with two or more values It is the surface acoustic wave filter described.

[0016]

[0017]

The present invention according to claim 4 is the surface acoustic wave filter according to claim 1 or 2 , characterized in that, in the unidirectional excitation electrode, the electrode finger pair is configured to satisfy (Equation 2). is there.

(Formula 2) γ> α + β and α <β where γ is the distance between the thin electrode finger and the thick electrode finger in the electrode finger pair, and α is the left end of the region where the IDT electrode is divided in half wavelength units and the thin electrode. The distance from the finger, β indicates the distance between the right end of the region where the IDT electrode is divided in half wavelength units and the thick electrode finger.

[0020] The present invention of claim 5, in the first or / and second non excitation electrode, the elastic of claim 2, characterized in that a configuration in which the electrode finger pairs satisfy the equation (3) It is a surface wave filter.

(Equation 3) γr> αr + βr where γr is the distance between the thin electrode finger and the thick electrode finger in the electrode finger pair, and αr is the distance between the left end of the area where the IDT electrode is divided in half wavelength units and the thin electrode finger. , Βr indicate the distance between the right end of the region where the IDT electrode is divided in half wavelength units and the thick electrode finger, respectively.

According to a sixth aspect of the present invention, in the first or / and the second non-excitation electrode, the electrode finger pair satisfies the formula (4), and the elasticity according to the second aspect. It is a surface wave filter.

(Equation 4) γr> αr + βr and αr <βr where γr is the distance between the thin electrode finger and the thick electrode finger in the electrode finger pair, and αr is the left end and the thin electrode of the region where the IDT electrode is divided in half wavelength units. The distance from the finger, βr, represents the distance between the right end of the region where the IDT electrode is divided in half wavelength units and the thick electrode finger.

According to a seventh aspect of the present invention, the interdigital transducer electrode includes at least one of a bidirectional electrode region and a dummy electrode region, and the bidirectional electrode has electrode fingers within one wavelength. The dummy electrode is composed of two or four electrode fingers having the same line width, and the dummy electrode is an electrode composed of four electrode fingers having the same line width within one wavelength. The surface acoustic wave filter according to any one of claims 1 to 6 .

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The surface acoustic wave filter of the present invention comprises:
A piezoelectric substrate, and at least two interdigital transducer electrodes (hereinafter abbreviated as IDT electrodes) on the piezoelectric substrate, wherein at least one of the IDT electrodes includes a unidirectional excitation electrode and first and second non-excitation electrodes. And the one-wavelength basic cell of the first non-excitation electrode has the same electrode configuration as the one-wavelength basic cell of the unidirectional excitation electrode in the propagation direction of the surface acoustic wave, and It is characterized in that the one-wavelength basic cell of the second non-excitation electrode has an electrode configuration symmetrical with the one-wavelength basic cell of the unidirectional excitation electrode with respect to the propagation direction of the surface acoustic wave.

Embodiments of the surface acoustic wave filter according to the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a surface acoustic wave filter according to a first embodiment of the present invention. In FIG. 1, 101 is a piezoelectric substrate, and input and output interdigital transducer electrodes (hereinafter referred to as IDT electrodes) are formed on the piezoelectric substrate 101, and the input IDT electrode 102 and the output IDT electrode 103 are separated by a predetermined distance. A surface acoustic wave filter is configured by disposing and arranging.

The input IDT electrode 102 has a structure including a unidirectional excitation electrode basic cell 104, a first non-excitation electrode basic cell 105, and a second non-excitation electrode basic cell 106. Cell 104, first non-excitation electrode basic cell 105, and second non-excitation electrode basic cell 10
6, each basic cell is based on one wavelength (1λ).

The output IDT electrode 103 is composed of a unidirectional excitation electrode basic cell 107 and a first non-excitation electrode basic cell 10
8 and a second non-excitation electrode basic cell 109, and in the unidirectional excitation electrode basic cell 107, the first non-excitation electrode basic cell 108, and the second non-excitation electrode basic cell 108, Each basic cell has one wavelength (1λ)
Is the basis. Here, the non-excitation electrode is an electrode that does not contribute to the excitation of the surface acoustic wave.

FIG. 2 is a schematic view of the above basic cell.
(A) is a unidirectional excitation electrode basic cell 104, FIG. 2 (b)
Is the first non-excitation electrode basic cell 105, and FIG.
The non-excitation electrode basic cell 106 of FIG.

In FIG. 2A, the unidirectional excitation electrode basic cell 104 has three electrode fingers within 1λ, and the first electrode finger 201 and the second electrode finger 202 are electrode widths. Is λ / 8 width, the third electrode finger 203 is λ / 4 width, the first electrode finger 201 and the third electrode finger 203 are connected to the lower extraction electrode 204, and the second electrode finger 203 is Electrode finger 20
2 is connected to the upper extraction electrode 205, and is connected to the second electrode finger 202, the first electrode finger 201, and the third electrode finger 20.
3 has a structure intersecting with 3 and excites a surface acoustic wave in this unidirectional excitation electrode basic cell 104.

In FIG. 2B, the electrode finger structure in the first non-excitation electrode basic cell 105 is similar to that of the unidirectional excitation electrode basic cell 104 in FIG. 202 is the first and third electrode fingers 201, 2
The difference is that it is connected to the same lower extraction electrode 204 as 03, the electrode fingers do not intersect, and the surface acoustic wave is not excited. Further, in FIG. 2C, the second non-excitation electrode basic cell 106 has a bilaterally symmetrical structure with respect to the first non-excitation electrode basic cell 105.

The operation of the surface acoustic wave filter configured as described above will be described below.

FIG. 3 is a schematic view of the arrangement of respective basic cells. FIG. 3A shows an arrangement example of the unidirectional excitation electrode basic cell 104 and the first non-excitation electrode basic cell 105.
The non-excitation electrode basic cell 105 is arranged. in this case,
The λ / 4 width electrode finger 301a in the unidirectional excitation electrode basic cell 104 and the λ / 4 width electrode finger 301b in the first non-excitation electrode basic cell 105 act as reflectors, and the distance between them is λ, The reflected wave by the non-excited electrode basic cell 105 has the same directionality as the unidirectional excited electrode basic cell 104, and the unidirectional excited electrode basic cell 104 excites a strong wave to the right. The reflected wave by the non-excitation electrode basic cell 105 of 1 becomes a strong reflected wave in the same right direction.

FIG. 3B shows an arrangement example of the unidirectional excitation electrode basic cell 104 and the second non-excitation electrode basic cell 106.
The second non-excitation electrode basic cell 106 of is arranged. In this case, λ / 4 in the unidirectional excitation electrode basic cell 104
The width electrode finger 302a and the λ / 4 width electrode finger 302b in the second non-excitation electrode basic cell 106 act as a reflector,
The interval is 1.5λ, and the non-excitation electrode basic cell 106
The reflected wave due to has a directionality opposite to that of the unidirectional excitation electrode basic cell 104, and the unidirectional excitation electrode basic cell 104 excites a strong wave in the right direction, whereas the second non-excitation electrode basic cell 104 The reflected wave from the cell 106 becomes a strong reflected wave in the opposite left direction.

Regarding the output IDT electrode 103,
Unidirectional excitation electrode basic cell 107, first non-excitation electrode basic cell 108, and second non-excitation electrode basic cell 109
However, the unidirectional excitation electrode basic cell 104, the first non-excitation electrode basic cell 105, and the second non-excitation electrode basic cell 106 have a symmetrical configuration.

By constructing the input IDT electrode 102 by the unidirectional excitation electrode basic cell 104, the first non-excitation electrode basic cell 105, and the second non-excitation electrode basic cell 106 as described above, the elasticity can be improved. The degree of freedom in design is improved by performing directional weighting by the reflection of surface waves, and further, input and output using the first non-excitation electrode basic cell 105 and the second non-excitation electrode basic cell 106. By folding back the propagation paths in the IDT electrodes 102 and 103, sufficient weighting necessary for the filter characteristics can be given even if the IDT electrode length is shortened, and the filter size can be reduced.

Further, the unidirectional excitation electrode basic cell 104, the first non-excitation electrode basic cell 105, and the second non-excitation electrode basic cell 106 have the same electrode configuration or a symmetrical configuration within 1λ. The acoustic velocity of surface acoustic waves can be made equal in the cell, and the frequency characteristic can be improved.

FIG. 4 is a pass characteristic diagram of the filter in this embodiment. A quartz substrate is used as the piezoelectric substrate. In FIG. 4, the vertical axis represents the attenuation amount, the horizontal axis represents the frequency, the solid line represents the pass characteristic of the surface acoustic wave filter of the present invention, and the broken line represents the pass characteristic of the surface acoustic wave filter in the conventional example. . In FIG. 4, the surface acoustic wave filter of the present invention has a band width of −5 dB attenuation from the center frequency (f ₀ ) of 1.32 MHz, which is a wider band characteristic than the conventional 1.18 MHz. .
As described above, the surface acoustic wave filter of the present invention realizes a wider band and flatness of the in-band characteristics as compared with the conventional example.

The unidirectional excitation electrode basic cell may be constructed as shown in FIG. In FIG. 5, the unidirectional excitation electrode basic cell 501 has three electrode fingers within 1λ, and the first electrode finger 502 and the second electrode finger 503 have an electrode width of λ / 8 width. Yes, the third electrode finger 504 is λ / 4 wide, and the first electrode finger 504 and the third electrode finger 504 are
Is connected to the lower extraction electrode 505, the second electrode finger 203 is connected to the upper extraction electrode 506, and the first electrode finger 502, the second electrode finger 503, and the third electrode finger 504 are It has a crossed structure, and a surface acoustic wave is excited in this unidirectional excitation electrode basic cell 104.

Incidentally, this unidirectional excitation electrode basic cell 50
1 has a configuration in which the unidirectional excitation electrode basic cell 104 in FIG. 1 is shifted by λ / 2. It should be noted that, even if the basic cell structure is other than this, the same effect can be obtained in the present invention as long as the structure produces unidirectionality.

The number of the unidirectional excitation electrode basic cells, the first non-excitation electrode basic cells, and the second non-excitation electrode basic cells and the arrangement position in the IDT electrode are not limited to those in this embodiment. Instead, it is performed by optimal weighting for obtaining a desired filter characteristic.

Further, in the present embodiment, the IDT electrode is configured to include the unidirectional excitation electrode basic cell, the first non-excitation electrode basic cell, and the second non-excitation electrode basic cell, but it is not limited to this. Alternatively, a plurality of λ / 4 reflector electrodes or a plurality of λ / 8 width electrode fingers may be included in the dummy electrode. In addition to the unidirectional excitation electrode, as shown in FIG. 6 includes a bidirectional electrode cell 601 having two electrode fingers having the same electrode width within 1λ, or a bidirectional electrode 602 having four electrode fingers having the same electrode width within 1λ, as shown in FIG. 6B. Even in this case, the effect of weighting the reflected waves can be obtained in the same manner as the effect described in the present embodiment.

In this case, the excitation center of the unidirectional excitation electrode basic cell 104 and the bidirectional electrode basic cell 601,
In order to make the excitation center of 602 an integral multiple of λ,
As shown in (c) and FIG. 6 (d), a space 60 is provided between cells.
3, 604 may be provided. Although the electrode width is set to λ / 4 or λ / 8 in FIG. 6, other characteristics may be used as long as the characteristic shows bidirectionality.

Further, either the input or output IDT electrode may be configured so as not to include the second non-excitation electrode basic cell. Since the filter characteristic is obtained by multiplying the characteristics of the input IDT electrode and the output IDT electrode,
When the weighting of either the DT electrode or the output IDT electrode is sufficient, the IDT electrode of the present invention may be applied to either the input IDT electrode or the output IDT electrode.

Although the first and second non-excitation electrodes are connected to the lower extraction electrode, this may be the upper extraction electrode. Further, as shown in FIG. 7, it may be configured not to be connected to the upper and lower extraction electrodes, and in this case, the first and second non-excitation electrode basic cells 701 and 702 on the input side or the output side. Side first and second non-excitation electrode elementary cells 703, 7
Even if 04 is grounded, the same effect as the present invention can be obtained.

(Second Embodiment) FIG. 8 shows a surface acoustic wave filter according to a second embodiment of the present invention. In FIG. 8, reference numeral 801 denotes a piezoelectric substrate, input and output interdigital transducer electrodes (hereinafter referred to as IDT electrodes) are formed on the piezoelectric substrate 801, and the input IDT electrode 802 and the output IDT electrode 803 are separated by a predetermined distance. A surface acoustic wave filter is configured by disposing and arranging.

The input IDT electrode 802 has a structure including a unidirectional excitation electrode basic cell 804, a first non-excitation electrode basic cell 805, and a second non-excitation electrode basic cell 806. Cell 804, first non-excitation electrode basic cell 805, and second non-excitation electrode basic cell 80
6, each basic cell is based on one wavelength (1λ).

The output IDT electrode 803 has a structure including a unidirectional excitation electrode basic cell 807, a first non-excitation electrode basic cell 808, and a second non-excitation electrode basic cell 809. Cell 807, first non-excitation electrode basic cell 808, and second non-excitation electrode basic cell 80
In FIG. 9, each basic cell is based on one wavelength (1λ). Here, the non-excitation electrode is an electrode that does not contribute to the excitation of the surface acoustic wave.

FIG. 9 is a schematic view of the above basic cell.
(A) is a unidirectional excitation electrode basic cell 804, FIG. 9 (b)
Is a first non-excitation electrode basic cell 805, and FIG.
The non-excitation electrode basic cell 806 of FIG.

In FIG. 9A, the unidirectional excitation electrode basic cell 804 has four electrode fingers within 1λ, and the first electrode finger pair 901 is a thin electrode finger 901a and a thick electrode finger 901b. Composed of and. Also, the second electrode finger pair 9
02 is composed of a thin electrode finger 902a and a thick electrode finger 902b. The first electrode finger pair 901 is connected to the upper extraction electrode 904, the second electrode finger pair 902 is connected to the lower extraction electrode 903, and the first electrode finger pair 901 is connected.
And the second electrode finger pair 903 have a crossed structure,
A surface acoustic wave is excited in this unidirectional excitation electrode basic cell 804.

In FIG. 9B, the electrode finger structure in the first non-excitation electrode basic cell 805 is the same as that of the unidirectional excitation electrode basic cell 804 in FIG. 9A, but the first electrode finger Different in that both the pair 901 and the second electrode finger 902 are connected to the same lower extraction electrode,
The respective electrode finger pairs do not intersect and the surface acoustic wave is not excited. Further, in FIG. 9C, the second non-excitation electrode basic cell 806 has a bilaterally symmetrical structure with respect to the first non-excitation electrode basic cell 805.

In FIG. 9A, thin electrodes 901a,
The electrode finger width of 902a is L1, and the thick electrodes 901b and 902 are
When the electrode finger width of b is L2, in this case, L2 / L
By setting 1 to be larger than 1 and preferably in the range of 1.0 to 3.0, good unidirectionality in the right direction can be obtained. Furthermore, a thin electrode finger 901a and a thick electrode finger 902a
, And the distance between the thin electrode finger 901b and the thick electrode finger 902b is γ, the unidirectional excitation electrode basic cell 804 is divided into two, and a λ / 2 cell is considered.
The distance between the left end of the λ / 2 cell 905 including the electrode finger pair 901 and the left end of the λ / 2 cell 906 including the first electrode finger pair 902 is α, and the thick electrode finger 901b is And a λ / 2 cell 90 including a first electrode finger pair 901
5 and the distance between the thick electrode finger 902b and the right end of the λ / 2 cell 906 including the first electrode finger pair 902 are β, γ is larger than α + β, and the relationship of α <β is satisfied. To be satisfied. By setting α <β, the symmetry becomes excellent, the deviation in the pass band can be reduced, and the attenuation amount outside the pass band can be increased.

As for the values of α and β, for example, on a quartz substrate, the film thickness ratio (h) between the electrode finger film thickness h and the wavelength λ (h
/ Λ) is approximately 1% and L1 + L2 = λ / 4, α and β have the relationship shown in FIG. 9 (d).
In FIG. 9 (d), the vertical axis represents α and β normalized by λ / 16, α / (λ / 16) and β / (λ / 16), and the horizontal axis represents the line width ratio (L2). / L1). By determining α and β from the line width ratio, in the unidirectional excitation electrode basic cell 804, a strong wave is generated on the right side due to the phase relationship between the excitation center and the reflection center of the surface acoustic wave.

If the film thickness ratio (h / λ) changes,
These α / (λ / 16) and β / (λ / 16) also change, but γ is larger than α + β, and the relationship of α <β is the same regardless of the film thickness ratio (h / λ). .

The operation of the surface acoustic wave filter configured as described above will be described below.

FIG. 10 is a schematic view of the arrangement of each basic cell. FIG. 10A is an arrangement example of the unidirectional excitation electrode basic cell 804 and the first non-excitation electrode basic cell 805. The first non-excitation electrode basic cell 805 is arranged on the right side of the unidirectional excitation electrode basic cell 804. Are placed. In this case, the reflection center in the unidirectional excitation electrode basic cell 104 and the reflection center in the first non-excitation electrode basic cell 805 have the same phase relationship, and the first non-excitation electrode basic cell 8
The reflected wave by 05 has the same directionality as the unidirectional excitation electrode basic cell 804, and the unidirectional excitation electrode basic cell 804 excites a strong wave in the right direction, whereas the first non-excitation electrode basic cell 804 The reflected wave from the cell 805 becomes a strong reflected wave in the same right direction.

FIG. 10B shows an arrangement example of the unidirectional excitation electrode basic cell 804 and the second non-excitation electrode basic cell 806. The second unidirectional excitation electrode basic cell 804 has a second cell on the right side. Two non-excitation electrode basic cells 806 are arranged. In this case, the reflection center in the unidirectional excitation electrode basic cell 804 and the reflection center in the second non-excitation electrode basic cell 806 have a reverse phase relationship, and the non-excitation electrode basic cell 80
The reflected wave by 6 has the opposite directionality to the unidirectional excitation electrode basic cell 804, and the unidirectional excitation electrode basic cell 804 excites a strong wave in the right direction, whereas the second non-excitation electrode The reflected wave from the basic cell 806 becomes a strong reflected wave in the opposite left direction.

Regarding the output IDT electrode 803,
Unidirectional excitation electrode basic cell 807, first non-excitation electrode basic cell 808, and second non-excitation electrode basic cell 809
However, the unidirectional excitation electrode basic cell 804, the first non-excitation electrode basic cell 805, and the second non-excitation electrode basic cell 806 have a symmetrical configuration with respect to the input IDT electrode 802.

By constructing the input IDT electrode 802 by the unidirectional excitation electrode basic cell 104, the first non-excitation electrode basic cell 805, and the second non-excitation electrode basic cell 806 as described above, elasticity can be obtained. The degree of freedom in design is improved by performing directional weighting based on the reflection of surface waves, and further, input and output using the first non-excitation electrode basic cell 805 and the second non-excitation electrode basic cell 806. By folding back the propagation path in the IDT electrodes 802 and 803, the IDT electrode length can be shortened and the filter size can be reduced.

Further, the unidirectional excitation electrode basic cell 804, the first non-excitation electrode basic cell 805, and the second non-excitation electrode basic cell 806 have the same electrode configuration within 1λ or a symmetrical configuration. The acoustic velocity of surface acoustic waves can be made equal in the cell, and the frequency characteristic can be improved.

The number of the unidirectional excitation electrode basic cells, the first non-excitation electrode basic cells, and the second non-excitation electrode basic cells and the arrangement position in the IDT electrode are not limited to those in this embodiment. Instead, it is performed by optimal weighting for obtaining a desired filter characteristic. In addition, in this embodiment, the IDT electrode is composed of the unidirectional excitation electrode basic cell and the first cell.
The non-excitation electrode basic cell and the second non-excitation electrode basic cell are included, but the present invention is not limited to this, and a plurality of λ / 8 width electrode fingers may be included as dummy electrodes.
In addition to the unidirectional excitation electrode, as shown in FIG. 11A, a bidirectional electrode cell 601 having two electrode fingers of the same electrode width within 1λ, or as shown in FIG. 11B. Even if the bidirectional electrode 602 having four electrode fingers having the same electrode width is included in 1λ, the effect of weighting the reflected waves can be obtained in the same manner as the effect described in the present embodiment.

Further, either the input or output IDT electrode may be configured not to include the second non-excitation electrode basic cell. Since the filter characteristic is obtained by multiplying the characteristics of the input IDT electrode and the output IDT electrode,
When the weighting of either the DT electrode or the output IDT electrode is sufficient, the IDT electrode of the present invention may be applied to either the input IDT electrode or the output IDT electrode.

Although the first and second non-excitation electrodes are connected to the lower extraction electrode, this may be the upper extraction electrode. Further, as shown in FIG. 12, the structure may be such that it is not connected to the upper and lower extraction electrodes, and in this case, the first and second non-excitation electrode basic cells 1201 and 120 on the input IDT side.
2, or the first and second non-excitation electrode basic cells 1203 and 1204 on the output IDT side are grounded, the same effect as the present invention can be obtained.

In this embodiment, the unidirectional excitation electrode basic cell 804 and the first non-excitation electrode basic cell 80
5 has the same electrode structure with respect to the propagation direction, and the second non-excited electrode basic cell 806 has a bilaterally symmetrical structure with respect to the propagation direction. As shown in FIG. 13, the line width ratio is L2 / L1.
Unidirectional excitation electrode basic cell 804 which is
The line width ratio of the non-excitation electrode basic cell 1301 of Lr2 / L
The reflectance may be changed as r1.

In this case, the interval between the thin electrode finger 1302a and the thick electrode finger 1302b is set to γr, the non-excitation electrode basic cell 1301 is divided into two, and a λ / 2 cell 1303 is considered, and the thin electrode finger 1302a and the λ / 2 cell are considered. The distance from the left end of 1303 is αr, the thick electrode finger 1302b and the λ / 2 cell 1303.
Γr is larger than αr + βr, and satisfies the relationship of αr <βr. By setting αr <βr, the symmetry becomes excellent, the deviation in the pass band can be made small, and the attenuation outside the pass band can be made large. Further, the second non-excitation electrode basic cell 1301 has a bilaterally symmetrical structure with the first non-excitation electrode basic cell 1301.

Further, the ID constituting the surface acoustic wave filter
In the T electrode, the first non-excitation electrode basic cell 1401 has a plurality of line width ratios (Lr2 / Lr1) and (Lr2a /) with respect to the unidirectional excitation electrode basic cell 1401 having a line width ratio of L2 / L1.
Lr1a) and a plurality of types of non-excitation electrode basic cells having a structure may be included. In this case, the reflectance in the non-excitation electrode basic cell can be changed, which further improves the degree of freedom in design.

The non-excitation electrode basic cell is shown in FIG.
As shown in FIG. 4 (a), the first non-excitation electrode λ / 2 cell 1
A structure in which a second non-excitation electrode λ / 2 cell 1402 is arranged on the right side of 401, or a second non-excitation electrode λ / 2 cell 1402 is formed on the left side of the first non-excitation electrode λ / 2 cell 1401.
It does not matter even if the structure is lined up.

In FIG. 14, the first non-excitation electrode λ / 2
The cell 1401 has the same structure as the λ / 2 cell 905 in the first non-excitation electrode basic cell in FIG. 9, and the second non-excitation electrode λ / 2 cell 1402 has the first non-excitation electrode λ /.
It is a bilaterally symmetrical structure of two cells 1401.

In the present embodiment, the relationship between α and β was described as h / λ being approximately 1% and L1 + L2 = λ / 4, but h / λ may be any other film thickness ratio, and , L1 + L2 is also λ / 4 other than, α <
If β is satisfied, the same effect as the present invention can be obtained.

Although the crystal substrate is used as the piezoelectric substrate in the embodiment of the present invention, LiTaO is used.
The same effect can be obtained by using another piezoelectric substrate such as ₃ or Li ₂ B ₄ O ₇ . In addition, La ₃ Ga ₅ SiO ₁₄ and La ₃ Ga
Against _5.5 Nb _0.5 O _14, substrate La ₃ periodically arranged only unidirectional Ta _{0. 5} Ga _5.5 O ₁₄ electrode fingers by crystal anisotropy of the substrate, such as is obtained, the electrode arrangement is different A similar effect can be obtained in terms of weighting by reflection.

With respect to the structure of the unidirectional excitation electrode of the surface acoustic wave in this embodiment, the surface acoustic wave excitation efficiency is improved as compared with the unidirectional excitation electrode in the first embodiment, and it is further reduced. It is possible to realize loss.

[0073]

As is apparent from the above description,
According to the present invention, it is possible to provide a small-sized surface acoustic wave filter having excellent selectivity characteristics in a wide pass band.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a surface acoustic wave filter according to a first embodiment of the present invention.

FIG. 2 (a) Schematic diagram of unidirectional excitation electrode basic cell (B) Schematic diagram of the first non-excitation electrode basic cell (C) Schematic diagram of the second non-excitation electrode basic cell

FIG. 3A is a layout diagram of a unidirectional excitation electrode basic cell and a first non-excitation electrode basic cell, and FIG. 3B is a layout diagram of unidirectional excitation electrode basic cell and a second non-excitation electrode basic cell.

FIG. 4 is a pass characteristic diagram of the surface acoustic wave filter of the present invention.

FIG. 5 is another configuration diagram of the unidirectional excitation electrode cell.

6A is a diagram showing a bidirectional electrode basic cell having two electrode fingers within one wavelength, and FIG. 6B is a diagram showing a bidirectional electrode basic cell having four electrode fingers within one wavelength. Layout of directional excitation electrode basic cell and bidirectional electrode basic cell 601 (d) Layout of unidirectional excitation electrode basic cell and bidirectional electrode basic cell 602

FIG. 7 is another configuration diagram of the surface acoustic wave filter according to the first embodiment of the present invention.

FIG. 8 is a configuration diagram of a surface acoustic wave filter according to a second embodiment of the present invention.

FIG. 9 (a) Schematic diagram of unidirectional excitation electrode basic cell (b) Schematic diagram of first non-excitation electrode basic cell (c) Schematic diagram of second non-excitation electrode basic cell (d) h / λ = 1 Α / (λ / 16), β / (λ /
The figure showing the line width ratio characteristic of 16)

FIG. 10 (a) Layout of unidirectional excitation electrode basic cell and first non-excitation electrode basic cell (b) Layout of unidirectional excitation electrode basic cell and second non-excitation electrode basic cell

FIG. 11 (a) Layout of unidirectional excitation electrode basic cell and bidirectional electrode basic cell 601 (b) Layout of unidirectional excitation electrode basic cell and bidirectional electrode basic cell 602

FIG. 12 is another configuration diagram of the surface acoustic wave filter according to the second embodiment of the present invention.

FIG. 13 is another configuration diagram of the first non-excitation electrode basic cell.

FIG. 14A is another configuration diagram of a non-excitation electrode basic cell. (B) Another configuration diagram of the non-excitation electrode basic cell

FIG. 15 is a block diagram of a conventional surface acoustic wave filter.

[Explanation of symbols]

101,801 Piezoelectric substrate 102,802 Input IDT electrode 103,803 Output IDT electrode 104,804 Unidirectional excitation electrode basic cell 105,701,805,1201 First non-excitation electrode basic cell 106,702,806,1202 No. 2 non-excitation electrode basic cell 107, 807 Output side unidirectional excitation electrode basic cell 108, 703, 808, 1203 Output side first non-excitation electrode basic cell 109, 704, 809, 1204 Output side second Non-excited electrode basic cells 201, 502 First electrode fingers 202, 503 Second electrode fingers 203, 504 Third electrode fingers 204, 505, 903 Lower extraction electrodes 205, 506, 904 Upper extraction electrodes 301a λ / 4 width electrode finger 301b λ / 4 width electrode finger 302a λ / 4 width electrode finger 302b λ / 4 width electrode finger 501 Tropism basic cell 601 bidirectional electrode base cell 602 bidirectional electrode base cell 603 cell interval 604 cell interval 901 first electrode finger pairs 901a, 902a thin electrode finger 901b, 902b thick electrode finger 902 second electrode finger pairs

Front Page Continuation (72) Inventor Shigeru Tsuzuki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Tsutomu Igaki 1006, Kadoma, Kadoma City, Osaka Prefecture (72) ) Inventor Ken Matsunami, 1006, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP 11-266138 (JP, A) JP 11-243324 (JP, A) JP 9-298441 (JP, A) JP 61-6917 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03H 9/145 H03H 9/64

Claims (7)

(57) [Claims] 1. A piezoelectric substrate and at least two interdigital transducer electrodes on the piezoelectric substrate, wherein at least one of the interdigital transducer electrodes comprises a unidirectional excitation electrode and first and second non-excitation electrodes. And the one-wavelength basic cell of the first non-excitation electrode has the same electrode configuration as the one-wavelength basic cell of the unidirectional excitation electrode with respect to the propagation direction of the surface acoustic wave, and the second bullet 1 wavelength basic cell of the non-excitation electrode is an electrode structure of a left-right symmetrical with respect to the propagation direction of the wave basic cell and the surface acoustic wave of the unidirectional excitation electrode
Surface acoustic wave filter, wherein the unidirectional excitation electrode has one wavelength basic cell having four electrode fingers.
And the four electrode fingers are two electrode fingers.
Forming a pair, and the two electrode finger pairs are lines of adjacent electrode fingers.
The width is different, and the line width (L1) of the thin electrode finger and the thick electrode finger
The line width ratio (L2 / L1) of the pole line width (L2) is greater than 1.
In the unidirectional excitation electrode, the electrode finger pair has
A surface acoustic wave filter having a satisfying configuration . (Equation 1) γ> α + β However, γ is a thin electrode finger and a thick electrode finger in the electrode finger pair.
The distance between them, α is the area where the IDT electrode is divided into half wavelength units.
Distance between the left edge of and the thin electrode finger, β is the half wavelength of the IDT electrode
The distance between the right edge of the area divided by the unit and the thick electrode finger
Show each. 2. A piezoelectric substrate, and at least two interdigital transducer electrodes on the piezoelectric substrate, wherein at least one of the interdigital transducer electrodes comprises a unidirectional excitation electrode and first and second non-excitation electrodes. And the unidirectional excitation electrode is configured such that the one-wavelength basic cell has four electrode fingers, and the four electrode fingers form two pairs of electrode fingers, and the two electrodes In the finger pair, the line widths of the adjacent electrode fingers are different, and the line width of the thin electrode finger (L1) and the line width of the thick electrode finger (L
The line width ratio (L2 / L1) in 2) is larger than 1, and the first and second non-excitation electrodes have a structure in which one wavelength basic cell has four electrode fingers. The electrode fingers form two electrode finger pairs, and the line widths of adjacent electrode fingers in the two electrode finger pairs are different from each other, and the thin reflector electrode finger has a line width (Lr1) and the thick reflector electrode finger has a line width. Width (Lr2)
Has a line width ratio (Lr2 / Lr1) of more than 1, and the one-wavelength basic cell of the first non-excitation electrode is the second wavelength
Surface acoustic wave filter having a symmetrical structure with respect to the propagation direction of the surface acoustic wave and the one-wavelength basic cell of the non-excitation electrode
And the electrode finger pair satisfies (Equation 1) in the unidirectional excitation electrode.
A surface acoustic wave filter having the above structure. (Equation 1) γ> α + β However, γ is a thin electrode finger and a thick electrode finger in the electrode finger pair.
The distance between them, α is the area where the IDT electrode is divided into half wavelength units.
Distance between the left edge of and the thin electrode finger, β is the half wavelength of the IDT electrode
The distance between the right edge of the area divided by the unit and the thick electrode finger
Show each. 3. The surface acoustic wave filter according to claim 2 , wherein the first or / and the second non-excitation electrode has a region where the line width ratio (Lr1 / Lr2) has two or more values. . 4. The unidirectional excitation electrode, wherein the electrode finger pair has a structure satisfying (Equation 2).
The surface acoustic wave filter according to 1 or 2 . (Equation 2) γ> α + β and α <β where γ is the distance between the thin electrode finger and the thick electrode finger in the electrode finger pair, and α is the left end of the region where the IDT electrode is divided in half wavelength units and the thin electrode finger. The distance and β indicate the distance between the right end of the region where the IDT electrode is divided in half wavelength units and the thick electrode finger, respectively. 5. The surface acoustic wave filter according to claim 2 , wherein the first or / and the second non-excitation electrode has a configuration in which the electrode finger pair satisfies (Equation 3). (Equation 3) γr> αr + βr where γr is the distance between the thin electrode finger and the thick electrode finger in the electrode finger pair, r is the distance between the left end of the region where the IDT electrode is divided in half wavelength units and the thin electrode finger, and βr is The distances between the right end of the region where the IDT electrode is divided in half wavelength units and the thick electrode finger are shown. 6. The surface acoustic wave filter according to claim 2 , wherein the first or / and the second non-excitation electrode has a structure in which the electrode finger pair satisfies (Equation 4). (Equation 4) γr> αr + βr and αr <βr where γr is the distance between the thin electrode finger and the thick electrode finger in the electrode finger pair, and αr is the left end of the area where the IDT electrode is divided in half wavelength units and the thin electrode finger. The distance and βr indicate the distance between the right end of the area where the IDT electrode is divided in half wavelength units and the thick electrode finger. 7. The interdigital transducer electrode is configured to include at least one of a bidirectional electrode region and a dummy electrode region, and the bidirectional electrode has two electrode fingers having the same line width within one wavelength. while being constructed according to the present or four electrode fingers, dummy electrodes claim 1, wherein the line width of the electrode fingers is an electrode composed of the same four electrode fingers in one wavelength 6 Which of
The surface acoustic wave filter according to any.