JP2000224002A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave device having a good band characteristic and an out-band characteristic, in which spurious signals resulting from high-order mode oscillations are suppressed. SOLUTION: Relating to a surface acoustic wave device in which plural surface acoustic wave filters 10 and 20 each of which is composed of a reflector 12a (22a), an IDT electrode 11a (21a) for input, an IDT electrode 11b (12b) for output, and a reflector 12b (22b) are connected to each other, pitches L1 and L2 of the electrode fingers of reflectors 12a and 22a (12b and 22b) and the IDT electrodes 11a and 21a for input (IDT electrodes 11b and 21b for output) are made different from each other.

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 device, and more particularly to a longitudinally coupled resonator type surface acoustic wave device.

[0002]

2. Description of the Related Art A surface acoustic wave filter constituting a conventional longitudinally coupled resonator type surface acoustic wave device comprises an input interdigital electrode (input IDT electrode) and an output interdigital electrode (output) on a piezoelectric substrate. IDT electrodes) are arranged along the propagation direction of the SAW, and IDT electrodes for input and output are arranged on both sides of the IDT electrodes for output and IDT electrodes. It is configured. Generally, the input IDT electrode and the output IDT electrode are configured such that electrode fingers having different potentials mesh with each other. The width of each electrode finger and the interval between the electrode fingers are set to １ ／ λ (wavelength λ: wavelength of a standing wave in the first mode).

[0003] Such a surface acoustic wave filter is a resonator type surface acoustic wave filter formed on a piezoelectric substrate by a plurality of longitudinal couplings (an input IDT electrode and an output IDT electrode propagates an elastic wave). There is a type in which an input IDT electrode and an output IDT electrode are sandwiched by a single reflector, and the vibration energy of a predetermined elastic wave is confined by a predetermined elastic wave in a pair of reflectors. In addition, in the pair of reflectors, in addition to the first mode and the second mode that form the pass frequency range, vibrations of higher modes exist as standing waves.

As a surface acoustic wave device using a plurality of surface acoustic wave filters having such a structure, for example, a surface acoustic wave device in which a plurality of two surface acoustic wave filters are connected in series in order to increase the attenuation level is known. (Japanese Patent Laid-Open No. 9-
294049). This schematic is shown in FIG.

In FIG. 9, reference numeral 1 denotes a piezoelectric substrate, 10 'denotes a first surface acoustic wave filter, and 11a denotes an input IDT.
Electrode, 11b is IDT electrode for output, 12a is ID for input
A reflector close to the T electrode 11a, 12b is an output IDT
A reflector electrode close to the electrode 11b. Also, 20 '
Is a second surface acoustic wave filter, and 21a is an input I
A DT electrode, 21b is an output IDT electrode, 22a is a reflector close to the input IDT electrode 21a, and 22b is an output IT electrode.
This is an interdigital reflector close to the DT electrode 21b.

In FIG. 9, the output IDT electrode 11b of the first surface acoustic wave filter 10 'and the input IDT electrode 21a of the second surface acoustic wave filter 20' are connected by a connection conductor film 15. Thereby, both surface acoustic wave filters 10 'and 20' are connected in series.

As another structure, a surface acoustic wave device in which a plurality of longitudinally coupled resonator type surface acoustic wave filters are connected in parallel to each other, for example, in order to reduce insertion loss, is known (Japanese Unexamined Patent Application Publication No. Hei 6 (1994)). -334476). The schematic diagram is shown in FIG.

In FIG. 10, 1 is a piezoelectric substrate, 30 'is a first surface acoustic wave filter, and 31a is an input ID.
T electrode, 31b is IDT electrode for output, 32a is I electrode for input
A reflector close to the DT electrode 31a, 32b is an output ID
The reflector electrode is close to the T electrode 31b. Also, 4
0 'is a second surface acoustic wave filter, 41a is an input IDT electrode, 41b is an output IDT electrode, 42a is a reflector close to the input IDT electrode 41a, 42b is close to the output IDT electrode 41b. It is an interdigital reflector.

In FIG. 10, the input IDT electrode 31a of the first surface acoustic wave filter 30 'and the input IDT electrode 41a of the second surface acoustic wave filter 40' are connected by the connection conductor film 35, and The output side IDT electrode 31b of the first surface acoustic wave filter 30 'and the output IDT electrode 41b of the second surface acoustic wave filter 40' are connected to each other by the connection conductor film 36.
0 'are connected in parallel.

In the surface acoustic wave filters 10 'and 20' connected in series in FIG. 9, for example, a reflector and an input / output ID
The electrode finger pitch between the T electrodes, that is, the pitch L between the electrode fingers that are close to each other between the reflector and the input / output IDT electrode has the same dimension L. It was the same for the surface acoustic wave filters 10 'and 20'.

That is, the pitch L between the electrode finger 120a of the reflector 12a of the surface acoustic wave filter 10 'and the electrode finger 110a of the input IDT electrode 11a and the surface acoustic wave filter 2
The pitch L between the electrode finger 220a of the 0 'reflector 22a and the electrode finger 210a of the input IDT electrode 21a is the same,
In addition, the electrode finger 120b of the reflector 12b of the surface acoustic wave filter 10 'and the electrode finger 110 of the output IDT electrode 11b.
and the pitch L between the electrode finger 220b of the reflector 22b of the surface acoustic wave filter 20 'and the electrode finger 210b of the output IDT electrode 21b was the same.

The same applies to the surface acoustic wave devices connected in parallel in FIG.

[0013]

However, Japanese Patent Laid-Open No. 9-2 discloses a surface acoustic wave device connected in series as shown in FIG.
In 94049, the input IDT electrode 11a and the output I
Since the parameters directly affecting the primary and secondary mode resonances forming the pass band, such as the logarithm of the cross electrode fingers of the DT electrode 11b, the cross width, and the electrode pitch, are changed, the characteristics of the pass band are changed. There was a problem.

Japanese Patent Application Laid-Open No. Hei 6-334476 discloses a surface acoustic wave device connected in parallel as shown in FIG. 10, although it is possible to improve the shoulder characteristic (attenuation pole characteristic) of the pass band, but to suppress the spurious. Is not disclosed.

That is, when an attempt is made to construct a double mode filter utilizing first-order and second-order mode resonance, high-order modes other than the first-order and second-order modes are present as spurious components, so that good attenuation characteristics are obtained. There is a problem that such a mode cannot be obtained, and such a higher-order mode suppresses spurious emission, and a good attenuation pole cannot be obtained.

The present invention has been devised in view of the above-described problems, and has a good band characteristic and a surface acoustic wave having an out-of-band characteristic in which a spurious signal due to higher-order mode vibration is suppressed. An apparatus is provided.

[0017]

According to the present invention, there is provided an input IDT electrode in which a first reflector electrode comprising a plurality of interdigital electrode fingers and electrode fingers having different potentials are engaged with each other on a piezoelectric substrate. A plurality of surface acoustic wave filters are formed by arranging an output IDT electrode composed of electrode fingers having different potentials meshing with each other and a second reflector electrode composed of a plurality of interdigital electrode fingers. In a surface acoustic wave device in which each surface acoustic wave filter is connected to each other,
That the electrode finger pitches between the first reflector electrode and the input IDT electrode and between the second reflector electrode and the output IDT electrode are different for each surface acoustic wave filter. This is a characteristic surface acoustic wave device.

The plurality of surface acoustic wave filters are connected in series with each other, and are provided between the first reflector electrode and the input IDT electrode and between the second reflector electrode and the output IDT.
The difference ΔLs between the electrode finger pitch and the T electrode is (0.01 + 0.5n) λ ≦ ΔLs ≦ (0.07 + 0...) With respect to the wavelength λ of the surface acoustic wave.
5n) λ (where n = 0, 1, 2,...).

Further, the plurality of surface acoustic wave filters are connected in parallel with each other, and are provided between the first reflector electrode and the input IDT electrode, and between the second reflector electrode and the output IDT electrode.
The difference ΔLp between the electrode finger pitch and the DT electrode is: (0.01 + 0.5n) λ ≦ ΔLp ≦ (0.04 + 0.
5n) λ (where n = 0, 1, 2,...).

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface acoustic wave device according to the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic plan view of a surface acoustic wave device according to the present invention in which a plurality of surface acoustic wave filters are connected in series, and FIG. 2 is a schematic plan view of a surface acoustic wave device in which a plurality of surface acoustic wave filters are connected in parallel. FIG.

In the figure, 1 is a piezoelectric substrate, 10 is a first surface acoustic wave filter, 11a is an input cross finger electrode (hereinafter simply referred to as an input IDT electrode), and 11b is an output cross finger electrode. (Hereinafter, simply referred to as an output IDT electrode), 12a is a first IDT electrode close to the input IDT electrode 11a.
IDT electrodes (hereinafter simply referred to as reflectors), 1
Reference numeral 2b denotes a second interdigital reflector electrode (hereinafter, simply referred to as a reflector) close to the output IDT electrode 11b. 20 is a second surface acoustic wave filter, 21a is an input IDT electrode, 21b is an output IDT electrode, 22a
Is an interdigital reflector electrode close to the input IDT electrode 21a, and 22b is an interdigital reflector electrode close to the output IDT electrode 21b.

The piezoelectric substrate 1 includes a piezoelectric single crystal substrate such as lithium niobate, lithium tantalate, and lithium tetraborate, a quartz substrate, and a piezoelectric ceramic substrate such as PZ (lead zirconate) and PZT (lead zirconate titanate). Etc. In the piezoelectric single crystal substrate and the quartz substrate, a predetermined cut is performed according to the crystal axis and the propagation direction, and in the piezoelectric ceramic substrate, a polarization process in a predetermined direction is performed according to the propagation direction.

On such a piezoelectric substrate 1, the first reflectors 12a (22a),
The input IDT electrode 11a (21a), the output IDT electrode 11b (21b), and the second reflectors 12b and 22b are arranged to form a plurality of surface acoustic wave filters 10 and 20.

For example, the first surface acoustic wave filter 10
(The upper side in FIG. 1) is a reflector 12a in which a plurality of electrode fingers are interdigitated from the left side, and an input IDT electrode 11 in which a plurality of electrode fingers having different potentials mesh with each other.
a, an output IDT electrode 11b in which a plurality of electrode fingers having different electric potentials are engaged with each other, and a plurality of electrode fingers in the form of an interdigitated reflector 12b are arranged side by side in this order. It is set in the wave propagation direction.
That is, the cutting direction and the polarization direction of the piezoelectric substrate 1 are adjusted,
And a reflector 12a, an input IDT electrode 11a, and an output I
Each electrode finger constituting the DT electrode 11b and the reflector 12b extends in a direction orthogonal to the propagation direction. Further, the second surface acoustic wave filter 20 (lower side in FIG. 1) has the same configuration.

From this, the first surface acoustic wave filter 1
0, the second surface acoustic wave filter 20 can be said to be a longitudinally coupled surface acoustic wave filter.

For example, in the surface acoustic wave filters 10 and 20, the reflectors 12a and 22 formed on the piezoelectric substrate 1 are provided.
a, the electrode fingers constituting the input IDT electrodes 11a and 21a, the output IDT electrodes 11b and 21b, and the reflectors 12b and 22b are formed by using a thin film metal photolithography technique.

Each of the electrodes 11a to 22b is made of, for example, aluminum and has a film thickness of the wavelength λ of the surface acoustic wave.
(Standard mode standing wave) and a film thickness (normalized film thickness) roughly defined by the characteristics of the substrate.

Reflectors 12a, 12b, 22a, 22b
Is configured such that a plurality of electrode fingers are arranged in an interdigitated manner.

The input IDT electrodes 11a and 21a and the output IDT electrodes 11b and 21b are configured such that a plurality of electrode fingers having different potentials mesh with each other.
The width of the electrode fingers having different potentials adjacent to each other and the interval between the electrode fingers are each set to ４λ. That is, the pitch of the electrode fingers is 1 / 2λ (0.5λ).

In FIG. 1, one electrode finger group constituting the input IDT electrode 11a is grounded, for example, and the other electrode finger group is on the hot side. Hereinafter, for convenience, one electrode finger group is called a ground side, the other electrode finger group is called a hot side, and the electrode finger of the input IDT electrode 11a closest to the reflection electrode 12a is 110a and the electrode finger of the input IDT electrode 11b is closest to the reflection electrode 12b. The electrode finger of the output IDT electrode 11b is denoted by 110b, the electrode finger of the input IDT electrode 21a closest to the reflective electrode 22a is denoted by 210a, and the electrode finger of the output IDT electrode 21b closest to the reflective electrode 22b is denoted by 210b. ,Also,
The input IDT electrodes 11a (2
1a) or the electrode fingers closest to the output IDT electrode 11b (21b) are placed at 120a, 120b, 220a, and 22.
0b.

The first surface acoustic wave filter 10 and the second surface acoustic wave filter 20 are connected to the connecting conductor film 1.
5 connected in series. For example, the electrode finger group on the other side of the output IDT electrode 11b of the first surface acoustic wave filter 10 is electrically connected to the electrode finger group on the other side of the input IDT electrode 21a of the second surface acoustic wave filter 20. It is connected.

This means for connecting in series is not limited to the various electrodes 11a to 22b in the case of using a conductor pattern as shown in FIG.
Are formed with the same metal material and in the same step. Other connection means include, for example, direct connection by wire bonding, indirect connection (for example, via a wiring pattern of an external circuit) by wire bonding, and connection to a wiring pattern of an external circuit board. The connection may be made by a connected solder bump or the like.

In the above-described surface acoustic wave device, the input IDT electrode 1 of the first longitudinally coupled resonator type surface acoustic wave filter 10 is used.
The signal input to 1a is output from the output IDT electrode 21b of the second longitudinally coupled resonator type surface acoustic wave filter 20 connected in series with the first longitudinally coupled resonator type surface acoustic wave filter 10. , And constitutes one filter circuit as a whole.

The present invention is characterized in that the reflector 12a and the input ID in the first surface acoustic wave filter 10 are provided.
The electrode finger pitch between the T electrode 11a, that is, the pitch between the electrode finger 120a of the reflector 12a and the electrode finger 110a of the input IDT electrode 11a (for example, the center in the width direction of the electrode finger 120a and the electrode finger 110a) Distance L1 and the reflector 22a in the second surface acoustic wave filter 20.
Electrode finger 220a and electrode finger 2 of input IDT electrode 21a
10a is different from the pitch L3.
Also, the output side IDT on the first surface acoustic wave filter 10 side
The above-described pitch L2 between the electrode 11b and the reflector 12b and the output-side IDT electrode 21 on the second surface acoustic wave filter 20 side
The above-mentioned pitch L4 between b and the reflector 22b is different from each other. In the surface acoustic wave filter 10, the pitches L1 and L2 may be the same, and in the surface acoustic wave filter 20, the pitches L3 and L4 may be the same.

As described above, in the longitudinally coupled resonator type surface acoustic wave filters 10 and 20, the pitches L1 and L3
By making (L2 and L4) different from each other, it is possible to make the frequencies of the higher-order mode spurious generated in the low frequency region (low band) side of the pass band different from each other.

By making the pitches L1 and L3 different, high-order mode spurs generated at these different frequencies are suppressed, and the amount of attenuation in the high-order mode spurious generation frequency region as a whole circuit is increased. It is. As a result, good attenuation characteristics can be obtained.

The present inventor has proposed the same surface acoustic wave filter 1
0 and 20, the pitches L1 and L2, and L3 and L
4 are the same (L1 = L2, L3 = L4), and the pitches L1 (L2) and L3 are set between the surface acoustic wave filters 10 and 20.
(L4), and the absolute value ΔLs of the difference was variously changed to obtain an optimum range of ΔLs.

As a result, when the wavelength of the surface acoustic wave is λ (the wavelength of the surface acoustic wave of the first mode), (0.01+
0.5n) λ ≦ ΔLs ≦ (0.07 + 0.5n) λ (where n = 0, 1, 2,...) (Where n = 0, 1, 2,...) Reduce spurious levels,
It has been found that good filter characteristics can be obtained.

FIGS. 3 and 4 show the filter characteristics at the center frequency 434.4 MHz of the surface acoustic wave device depending on the difference ΔLs, and FIG. 4 is a characteristic diagram in which the characteristics of the pass band are enlarged.

In FIG. 3, the characteristic a is the difference between the conventional surface acoustic wave device shown in FIG. 9 (the pitch L of the first surface acoustic wave filter and the pitch L of the second surface acoustic wave filter, and the difference is 0 ( ΔLs = 0λ).

The characteristics b to f are determined by the pitch L 1 of the first surface acoustic wave filter 10 and the second surface acoustic wave filter 2.
The absolute value ΔLs of the difference of the pitch L3 of 0 is 0.01λ ≦ ΔL
This shows the characteristics when s ≦ 0.09λ (n = 0 in the above equation).

As a result, when the absolute value ΔLs of the surface acoustic wave device is not 0 as in the first invention (characteristics b to f), compared to ΔLs = 0 as in the conventional surface acoustic wave device, 4
Spurious due to higher-order mode vibrations generated near 33.3 MHz can be effectively suppressed. Specifically, although the characteristic a does not provide a sufficient attenuation of about -26 dB, the characteristics b to f obtain a sufficiently large attenuation than -28 dB.

Thus, a surface acoustic wave device having excellent selectivity and capable of sufficiently suppressing spurious in the vicinity of the band can be obtained.

Further, by varying the pitch difference ΔLs with respect to the wavelength λ, the spurious level is further reduced, and the attenuation characteristics are improved. That is, the appropriate range of the difference ΔLs between the pitch L1 of the first surface acoustic wave filter 10 and the pitch L3 of the second surface acoustic wave filter 20 is:
0.01λ ≦ ΔLs ≦ 0.07λ (n = 0 in the above equation) (characteristics b to e).

If the pitch difference ΔLs is less than 0.01λ, it is difficult to sufficiently attenuate the spurious generated in the lower pass band as described above. For example, -28d
An attenuation larger than B cannot be expected. As a result, the surface acoustic wave device has poor selectivity.

The pass band tends to become narrower as the pitch difference ΔLs increases. For example, pitch difference Δ
If Ls exceeds 0.07λ, the pass band characteristics deteriorate, so that good pass band characteristics cannot be obtained.

Further, when the pitch difference ΔLs becomes 0.09λ as shown by the characteristic f in FIG. 4, the pass band characteristic is deteriorated, and a spurious level is generated in the vicinity of the pass band, so that sufficient suppression can be achieved. It will be difficult. This is 2
This is because the spurious due to the vibration of the higher-order mode existing on the low-frequency side of the two surface acoustic wave filters 10 and 20 becomes too close to the pass band.

As described above, the first surface acoustic wave filter 1
0 and the second surface acoustic wave filter 20 are connected in series, and when the filter characteristics (selectivity) are improved, the pitches L1, L3 (or L2, L
4) and the absolute value ΔLs of the pitch difference is (0.01 + 0.5n) λ ≦ ΔL
It is important that s ≦ (0.07 + 0.5n) λ.

Note that the present inventor has found that the pitch has a period related to 1 / 2λ, and therefore, in the above equation, even if n = 0, 1, 2, 3,. It was confirmed that excellent characteristics could be obtained. The same effect can be obtained by connecting in multiple stages such as three elements or four elements.

FIG. 2 shows a surface acoustic wave device in which a first longitudinally coupled type surface acoustic wave filter 30 and a second surface acoustic wave filter 40 are connected in parallel with each other.

In FIG. 2, one electrode finger group constituting the input IDT electrode 31a is, for example, grounded, and the other electrode finger group is on the hot side. Hereinafter, for convenience, one electrode finger group is called a ground side, the other electrode finger group is called a hot side, and the electrode finger of the input IDT electrode 31a closest to the reflection electrode 32a is 310a, and the electrode finger is closest to the reflection electrode 32b. The electrode finger of the output IDT electrode 31b is 310b, the electrode finger of the input IDT electrode 41a closest to the reflective electrode 42a is 410a, and the electrode finger of the output IDT electrode 41b closest to the reflective electrode 42b is 410b.

Further, the first surface acoustic wave filter 30 and the second surface acoustic wave filter 40 are connected in parallel with each other. For example, the electrode finger group on the other side of the input IDT electrode 31a of the first surface acoustic wave filter 30 and the electrode finger group on the other side of the input IDT electrode 41a of the second surface acoustic wave filter 40 are connected to a connection conductor. At the same time, they are connected by the film 35, and at the same time, the electrode finger group on the other side of the output IDT electrode 31b of the first surface acoustic wave filter 30 and the electrode finger on the other side of the output IDT electrode 41b of the second surface acoustic wave filter 40. The group and the connection conductor film 36 are connected to each other.

In FIG. 2, the connection conductor film 35 serves as an input terminal of an external circuit, and the connection conductor film 36
Output terminal of external circuit. The connection conductor films 35, 3
Reference numeral 6 denotes the same metal material when the various electrodes 31a to 42b are formed, and is formed in the same step.

In the above-described surface acoustic wave device, a signal commonly input to the input IDT electrode 31a of the first surface acoustic wave filter 30 and the input IDT electrode 41a of the second surface acoustic wave filter 40 is applied to the second surface acoustic wave filter. 1. Surface acoustic wave filter 30
And the output IDT electrode 41b of the second surface acoustic wave filter 40 are synthesized and output. Thereby, one filter circuit is constituted as a whole.

The feature of the present invention is that the electrode finger 32 of the reflector 32a in the first surface acoustic wave filter 30 is used.
0a and the pitch L1 between the electrode fingers 310a of the input IDT electrode 31a (for example, the distance between the centers of the electrode fingers of the electrode fingers 320a and 310a) and the reflector 42a in the second surface acoustic wave filter 40. L3 between the electrode finger 420a and the electrode finger 410a of the input IDT electrode 41a
Are different from each other. Also, the pitch L2 between the output-side IDT electrode 31b and the reflector 32b on the first surface acoustic wave filter 30 side and the output-side IDT electrode 41b and the reflector 42b on the second surface acoustic wave filter 40 side The pitch L4 is different from the above. In the surface acoustic wave filter 30, the pitches L1 and L2 are the same, and in the surface acoustic wave filter 40, the pitches L3 and L2 are equal.
4 may be the same.

As described above, the pitches L1, L3 (or L3)
2, L4), it is possible to make the frequencies of the higher-order mode spurious generated in the low frequency region (low frequency) side of the pass band different from each other.

The present inventor has variously changed the absolute value ΔLp of the difference between the pitches L1 and L3 (or the difference between L2 and L4) and determined the optimum range of ΔLp. As a result, when the wavelength of the surface acoustic wave is λ (the wavelength of the standing wave in the first mode), (0.01 + 0.5n) λ ≦ ΔLp ≦ (0.04 + 0.
5n) If λ (where n = 0, 1, 2,...) Is satisfied, the level of the higher-order mode spurious is reduced with almost no change in the pass band characteristics, and good filter characteristics are obtained. I realized that I can do it.

FIGS. 5 and 6 show the filter characteristics at the center frequency of 434.4 MHz in the surface acoustic wave device based on the difference ΔLp, and FIG. 6 is a characteristic diagram in which the pass band characteristics are enlarged.

5 and 6, the characteristic g is the difference between the conventional surface acoustic wave device shown in FIG. 10 (the pitch L of the first surface acoustic wave filter and the pitch L of the second surface acoustic wave filter). Indicates 0 (ΔLp = 0λ).

The characteristics h to l are obtained by setting the absolute value ΔLp of the difference between the pitch L3 of the first surface acoustic wave filter 30 and the pitch L4 of the second surface acoustic wave filter 40 to 0.01λ ≦
This shows the characteristics when ΔLp ≦ 0.05λ (n = 0 in the above equation).

As a result, when the absolute value ΔLp of the surface acoustic wave device is not 0 as in the first invention (characteristics h to l), the absolute value ΔLp is 4 compared to ΔLp = 0 as in the conventional surface acoustic wave device.
Spurious due to higher-order mode vibrations generated near 33.3 MHz can be effectively suppressed. Specifically, although the characteristic g does not provide a sufficient attenuation of about -16 dB, the characteristics h to l provide a sufficiently large attenuation than -17 dB.

Thus, a surface acoustic wave device having excellent selectivity and capable of sufficiently suppressing spurious in the vicinity of the pass band is obtained.

Further, by changing the pitch difference ΔLp variously with respect to the wavelength λ, the spurious level is further reduced, and the attenuation characteristics are improved. That is, the appropriate range of the difference ΔLp between the pitch L1 of the first surface acoustic wave filter 30 and the pitch L2 of the second surface acoustic wave filter 40 is:
0.01λ ≦ ΔLp ≦ 0.04λ (n = 0 in the above equation).

If the pitch difference ΔLp is less than 0.01λ, it is difficult to sufficiently attenuate the spurious generated in the lower pass band as described above. For example, -17d
An attenuation larger than B cannot be expected. As a result, the surface acoustic wave device has poor selectivity.

The pass band tends to become narrower as the pitch difference ΔLp increases. For example, pitch difference Δ
If Lp exceeds 0.04λ, the passband characteristics deteriorate, and good passband characteristics cannot be obtained. For example, FIG.
The pitch difference ΔLp is 0.05λ
Then, the pass band characteristics deteriorate.

This is because two surface acoustic wave filters 30,
This is because the frequency range of the spurious components due to the vibration of the higher-order mode existing on the low frequency side of the frequency band 40 becomes so large that the spurious components are generated near the pass band, and it is difficult to suppress the level. .

As described above, in a surface acoustic wave device in which the first surface acoustic wave filter 30 and the second surface acoustic wave filter 40 are connected in series, when the filter characteristics (selectivity) become good, the pitch It is important to make L1 and L2 (or L3 and L4) different from each other, and further, the absolute value of the pitch difference ΔLp is (0.01 + 0.5n) λ ≦ Δ
It is important that Lp ≦ (0.04 + 0.5n) λ.

Since the pitch has a period related to 1 / 2λ, the present inventor has the same irrespective of whether n = 0, 1, 2, 3,. It was confirmed that excellent characteristics could be obtained.

FIG. 7 shows a four-element surface acoustic wave filter 50,
It is a figure which shows the electrical connection state of the surface acoustic wave device which connected 60,70,80 mutually parallel. In the drawing, the surface acoustic wave filters 50, 60, 70, and 80 are arranged from the upper side, and when the pitches L5 and L7 are the same and the pitches L9 and L11 are the same, the pitches L5 (L7) and L9 (L11)
And Naturally, all pitches L5, L7, L
9, L11 may be different from each other. In this case, the maximum difference between the pitches L5, L7, L9, and L11 may satisfy the above expression. The output side pitch L6,
The same applies to L8, L10, and L12.

FIG. 8 is a characteristic diagram of the surface acoustic wave device shown in FIG. FIG. 8 shows the respective pitches L5 = L6 = L7 =
As L8, the pitch L9 = L10 = L11 = L1
2, with these pitches being different from each other, ΔL
FIG. 9 is a characteristic diagram when p is set to 0.03λ.

FIG. 11 shows that all the pitches in FIG. 7 are the same (L5 = L6 = L7 = L8 = L9 = L10 = L
11 is a characteristic diagram of a conventional surface acoustic wave filter in which 11 = L12).

As can be seen from a comparison between FIG. 8 and FIG. 11, the surface acoustic wave device of the present invention hardly changes the characteristics of the pass band, and the level of the higher-order mode spurious generated on the lower frequency side of the pass band. It can be seen that a good filter characteristic is obtained.

In particular, in order to reduce the insertion loss as compared with a surface acoustic wave device in which the above-described surface acoustic wave filters are connected in series or a surface acoustic wave device in which a plurality of surface acoustic wave filters are connected in parallel, a better pass band is provided. Characteristics can be realized.

The inventor of the present invention has confirmed that the same effect can be obtained by connecting three or five elements to another stage.

[0076]

As described above, according to the present invention, the input IDT electrode (output IDT electrode) of the surface acoustic wave filter is provided.
Since the pitches of the electrode fingers between the reflector and the reflector are made different from each other, the level of spurious due to higher-order mode vibration generated near the lower side of the pass band can be reduced, and good attenuation characteristics can be obtained.

In particular, in a surface acoustic wave device connected in series, the absolute value ΔL of the pitch difference is defined as (0.01 + 0.5n) λ ≦ ΔL ≦ (0.07+
0.5n) λ, the absolute value ΔL of the pitch difference is further increased in the surface acoustic wave devices connected in parallel.
With respect to the wavelength λ of the standing wave, (0.01 + 0.5n)
By setting λ ≦ ΔL ≦ (0.04 + 0.5n) λ, deterioration of band characteristics can be suppressed.

[Brief description of the drawings]

FIG. 1 is a plan view of a surface acoustic wave device of the present invention, that is, a surface acoustic wave device in which surface acoustic wave filters are connected in series.

FIG. 2 is a plan view of a surface acoustic wave device of the present invention, that is, a surface acoustic wave device in which surface acoustic wave filters are connected in parallel with each other.

FIG. 3 is a characteristic diagram showing an attenuation characteristic due to a difference in pitch in the surface acoustic wave device shown in FIG. 1;

FIG. 4 is a characteristic diagram showing a pass band characteristic of FIG. 3;

FIG. 5 is a characteristic diagram showing an attenuation characteristic due to a difference in pitch in the surface acoustic wave device shown in FIG. 2;

FIG. 6 is a characteristic diagram showing the pass band characteristics of FIG.

FIG. 7 is a diagram showing an electrical connection of a surface acoustic wave device of the present invention, that is, a surface acoustic wave device in which four surface acoustic wave filters are connected in parallel with each other.

FIG. 8 is a characteristic diagram showing an attenuation characteristic due to a difference in pitch in the surface acoustic wave device shown in FIG. 7;

FIG. 9 is a plan view of a conventional surface acoustic wave device, that is, a surface acoustic wave device in which surface acoustic wave filters are connected in series to each other.

FIG. 10 is a plan view of a conventional surface acoustic wave device, that is, a surface acoustic wave device in which surface acoustic wave filters are connected in parallel with each other.

FIG. 11 is a characteristic diagram showing attenuation characteristics of a conventional surface acoustic wave device, that is, a surface acoustic wave device in which four surface acoustic wave filters are connected in parallel with each other.

[Explanation of symbols]

10-80 Surface acoustic wave filter 1 Piezoelectric substrate 11a, 21a, 31a, 41a Input IDT electrode 11b, 21b, 31b, 41b Output IDT electrode 12a, 12b, 22a 22b, 32a, 32b, 4
2a, 42b ... Reflectors L1, L2, L3, L4, L5, L6, L7, L8, L
···pitch

Claims (3)

[Claims] 1. A first reflector electrode comprising a plurality of interdigital electrode fingers, an input IDT electrode formed by interdigitating electrode fingers having different potentials, and an electrode finger having different potentials on a piezoelectric substrate. Output IDTs configured to mesh with each other
An electrode and a second reflector electrode composed of a plurality of interdigital transducers are arranged to form a plurality of surface acoustic wave filters, and a surface acoustic wave device in which each surface acoustic wave filter is connected to each other; The electrode finger pitch between the first reflector electrode and the input IDT electrode and between the second reflector electrode and the output IDT electrode is different for each surface acoustic wave filter. Surface acoustic wave device. 2. The plurality of surface acoustic wave filters are connected in series with each other, and a first reflector electrode and the input I
The difference ΔLs between the electrode finger pitch between the DT electrode and between the second reflector electrode and the output IDT electrode is: (0.01 + 0.5n) λ ≦ ΔLs ≦ (0.07 + 0.
5n) The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is set to satisfy λ (where n = 0, 1, 2, ...). 3. The plurality of surface acoustic wave filters are connected in parallel with each other, and a first reflector electrode and the input I
The electrode finger pitch difference ΔLp between the DT electrode and between the second reflector electrode and the output IDT electrode is: (0.01 + 0.5n) λ ≦ ΔLp ≦ (0.04 + 0.
5n) The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is set to satisfy λ (where n = 0, 1, 2, ...).