JPH10294644A - Polar surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the attenuation gradient near a cutoff by setting at least one of vibration mode of one coupled multimode SAW filter constituting a resonance synthesis-type filter and as least one vibration mode of the other filter in such a way that resonance frequencies are equal and input/output phase shift quantity in the resonance frequencies differ by a specified value. SOLUTION: The filters A and B being vertically coupled triple mode SAW filters are electrically connected in parallel to constitute a resonance synthesis type SAW filter C. The filter B is arranged by shifting the electrode fingers of IDT4a by λ/2 so that the phase becomes opposite to that of the filter A. IDT2a-2c and 4a-4c are set so that the relation of the resonance frequencies of the filters A and B satisfies Fa1=Fb1 and Fa3=Fb2. Input/output phase shift quantity is varied by (2n+1)π, (n=0.1...). Thus, the resonance synthesis type SAW filter C whose attenuation gradient near the high band-side of the cutoff is steep can be provided.

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, and more particularly to a surface acoustic wave filter comprising a plurality of longitudinally coupled multimode filters connected in parallel to each other by providing an attenuation pole near a pass band. The present invention relates to a resonance type surface acoustic wave filter having a steep gradient.

[0002]

2. Description of the Related Art Recently, a surface acoustic wave filter (hereinafter referred to as SA) has been developed.
W filters) are excellent in miniaturization, higher frequency, mass productivity, and the like, and are therefore often used as RF and IF stage filters for wireless devices such as mobile phones. In particular, in addition to the conditions of the wideband filter, the first IF filter of a digital communication radio such as recent GSM and CDMA is used.
A sharper cutoff characteristic is required, and it is an important factor to have high selectivity for separating signals of adjacent channels.

FIG. 16A is a plan view showing a schematic electrode pattern of a conventional resonance-combination type SAW filter. Two IDTs 21a are arranged on a main surface of a piezoelectric substrate 20 along a propagation direction of a surface wave. 21c and grating 21b between them
And reflectors 22a and 22b are arranged on both sides of the IDT,
A longitudinally-coupled triple-mode filter A (filter A) is constructed using three modes generated as a result of acoustic coupling. As is well known, the three longitudinal modes resulting from acoustic coupling are changed from low order modes to A1 (first order), A2 (secondary) and A3 (third order).
And their resonance frequencies are Fa1, Fa2 and F2, respectively.
Assuming that a3 is used, in the longitudinally coupled multimode filter, the higher the higher-order mode, the higher its resonance frequency is generated on the lower frequency side. That is, the frequency relationship of Fa3 <Fa2 <Fa1 is satisfied. Similarly to the longitudinally coupled triple mode filter A, three IDTs 23 are arranged on the piezoelectric substrate 20 along the propagation direction of the surface wave.
a, 23b, 23c and reflectors 24a, 24b on both sides thereof
Are arranged, and a longitudinally coupled triple mode filter B (filter B) is configured using three modes resulting from acoustic coupling. The three modes of the filter B are changed from low order to B1 (1
Next, B2 (secondary) and B3 (third), and their resonance frequencies are Fb1, Fb2 and Fb3, Fb3 <F
b2 <Fb1.

The electrode fingers of the filter B are considered with respect to the IDT electrode fingers of the filter A so that the corresponding modes of the filters A and B, for example, the modes A1 and B1 have opposite phases. And place it. Further, the arrangement relationship between the resonance frequencies of the filters A and B is expressed as Fa2 = Fb
3. A so-called resonance combined type SAW filter C is configured by setting the period of the IDT electrode finger so that Fa1 = Fb2 and electrically connecting filters A and B in parallel. FIG. 16B shows a filter A for clarifying the resonance point.
And the transmission characteristics when the terminal impedances are mismatched. When the vertical axis represents loss (Loss) and the horizontal axis represents frequency, A1 (primary) and A2 (2
3) corresponding to the resonance frequencies of the (next) and A3 (third) modes.
Resonance peaks Fa1, Fa2, and Fa3 appear remarkably. The phase relationship between the above modes is as follows: if the phase of the A1 (primary) mode is 0 degree, the phase of the A2 (secondary) mode is 180 degrees;
The third (third-order) mode is 0 degree, and the vertical axis indicates the phase (Phas).
e), the frequency is plotted on the horizontal axis, as shown in FIG.

FIG. 16 (c) shows transmission characteristics when the terminal impedance of the filter B shown in FIG. 16 (a) is mismatched. As in FIG. ), Three resonance peaks Fb1 and Fb2 corresponding to the resonance frequencies of the B2 (secondary) and B3 (third) modes.
And Fb3 appear remarkably. The phase of these modes is
Since the filter B is arranged in consideration of the polarity of the IDT of the filter B so as to have a phase opposite to that of the corresponding mode of the filter A, the phase of the B1 (primary) mode is 180 degrees, and
(Second order) has a phase of 0 degrees, and B3 (third order) has a phase of 180 degrees. FIG. 16D shows transmission characteristics when the terminal impedance of the resonance combined type SAW filter C configured by electrically connecting the filters A and B electrically as shown in FIG. 16A is mismatched. And has four resonance peaks. By appropriately terminating the filter and matching the impedance, a filtering characteristic α of a fourth-order filter as shown in FIG. 17 can be obtained.
A curve β in the figure is a group delay time characteristic of the resonance combined type SAW filter C.

[0006]

However, in the above-mentioned conventional resonance-combined SAW filter, the problem is that the attenuation gradient near the cutoff is insufficient, for example, as required for the first IF of the digital communication system. There is. Also,
If the same type of filter is cascaded to satisfy the requirement, the attenuation gradient can be improved, but there is a problem that the insertion loss of the filter increases and the receiving performance of the radio device deteriorates. on the other hand,
A ladder-type SAW filter (ladder-type SAW filter) configured by connecting a SAW resonator formed by arranging reflectors on both sides of an IDT in a ladder-type configuration has a steep attenuation gradient because a polarized configuration is possible. A SAW filter can be realized. For this reason, recently, it is used for various wireless devices, but has a problem that it is not suitable for a system requiring a wide band filter such as a digital communication system because it has a narrower band than a SAW filter of a lattice type circuit. . SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and an object of the present invention is to provide a resonance combined type SAW filter having an improved attenuation gradient near a cutoff and a small insertion loss.

[0007]

According to a first aspect of the present invention, there is provided a polarized type surface acoustic wave filter according to the present invention, wherein at least two IDTs are reflected on a piezoelectric substrate and reflected outwardly. A resonant combined SAW filter comprising at least two coupled multi-mode SAW filters, each of which is configured by utilizing an acoustic coupling of a surface wave to be excited and disposed, and electrically connected in parallel. Mode S
At least one of the vibration modes of one multi-mode SAW filter of the AW filter and the other multi-mode SA
At least one of the vibration modes of the W filter has the same resonance frequency, and the phase shift between the input and the output at the resonance frequency is (2n + 1) π (n = 0, 1,
2) A polarized surface acoustic wave filter characterized by being different. The invention according to claim 2 is characterized in that the multi-mode S
2. The polarized surface acoustic wave filter according to claim 1, wherein the AW filter is a longitudinally coupled multi-mode SAW filter. The invention according to claim 3 is characterized in that the multi-mode S
An AW filter arranges an input / output IDT on a piezoelectric substrate along a propagation direction of a surface acoustic wave and reflectors on both sides thereof.
2. The polarized surface acoustic wave filter according to claim 1, wherein the filter is a longitudinally coupled multi-mode SAW filter having a grating disposed between T. The invention according to claim 4 is the polarized surface acoustic wave filter according to claim 1, wherein the multi-mode SAW filter is a transversely coupled multi-mode SAW filter. According to a fifth aspect of the present invention, there is provided a two-dimensional mode coupled multimode S in which the multimode SAW filter couples longitudinal mode resonance utilizing coupling in the propagation direction of a surface wave and transverse mode resonance perpendicular to the propagation direction.
2. The polarized surface acoustic wave filter according to claim 1, which is an AW filter. The invention according to claim 6 is characterized in that one of the multimode SAW resonator filters is a longitudinally coupled multimode SAW filter and the other is a transversely coupled multimode SAW filter. This is a surface acoustic wave filter. The invention according to claim 7, wherein one of the multimode SAW filters is a longitudinally coupled multimode SAW filter and the other is a two-dimensional mode coupled multimode SAW filter. This is a surface acoustic wave filter. Claim 8
2. The polarized surface acoustic wave filter according to claim 1, wherein one of the multi-mode SAW filters is a transversely coupled multi-mode SAW filter and the other is a two-dimensional mode-coupled multi-mode SAW filter. It is.
According to a ninth aspect of the present invention, there is provided a polarized surface acoustic wave filter comprising at least one polar surface acoustic wave filter according to any one of the first to eighth aspects.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1A is a schematic plan view showing a first embodiment of a resonance-combined SAW filter according to the present invention. First, two IDTs 2a, 2c and a grating 2b are arranged on the main surface of the piezoelectric substrate 1 along the propagation direction of the surface wave, and reflectors 3 are provided on both sides of the IDT.
a, 3b are arranged to constitute a longitudinally coupled triple mode SAW filter (filter A). In the filter A, three modes A1 (first order) of acoustic coupling between longitudinal modes,
If A2 (secondary) and A3 (third order) are strongly excited and their resonance frequencies are Fa1, Fa2 and Fa3, respectively, the frequency relationship in the longitudinal coupling mode is Fa3 <Fa2.
<Fa1. Next, similarly to the filter A, the two IDTs 4a, 4
The filter B is a longitudinally coupled triple mode SAW filter configured by arranging a grating 4b and the reflectors 5a and 5b on both sides of the IDT. Similarly to the filter A, three modes B1 (primary) and B2
(Second order) and B3 (third order) are strongly excited, and their resonance frequencies are Fb1, Fb2, and Fb3, respectively.
The frequency array becomes Fa3 <Fa2 <Fa1.

As shown in FIG. 1A, the filter B is
The electrode fingers of one of the two IDTs (the input side in FIG. 1A) are shifted by λ / 2 so as to have the opposite phase to the filter A. The filter A and the filter B are electrically connected in parallel to form a so-called resonance combined type SAW filter C. FIG. 1B shows transmission characteristics and phase characteristics when the terminal impedance of the filter A is mismatched, and FIG. 1C shows transmission characteristics and phase characteristics when the terminal impedance of the filter B is mismatched.
In order to change the frequency of each resonance point of the coupled multimode surface acoustic wave resonator, a method of changing the logarithm of the IDT, a method of shifting the input and output IDTs from a regularly arranged period, and a method of changing the electrodes are described. A known method such as a method of varying the film thickness may be appropriately combined. Here, FIG.
As shown in (c), the IDT of each of the filters A and B is set so that the relationship between the resonance frequencies of the filters A and B substantially satisfies the frequency relationship of Fa1 = Fb1 and Fa3 = Fb2.
Is set, the A1 mode (0 °) of the filter A and the B1 mode (180 °) of the filter B are out of phase with each other, and their resonance frequencies are substantially equal. Further, A3 of the filter A
The mode (0 °) and the B2 mode (0 °) of the filter B have the same phase and their resonance frequencies are almost equal. After setting the frequency and phase conditions as described above, when the filter A and the filter B are electrically connected in parallel, the resonance circuit of A3 mode and B
A two-mode resonance circuit is connected in parallel, and the frequency is almost F
a3 (= Fb2) is equivalent to a resonance circuit having an impedance of about 1/2.

Further, the A1 mode (0 °) resonance circuit and B
If a 1-mode (180 °) resonance circuit is connected in parallel, the phases are opposite to each other, so that the currents flowing through these circuits cancel each other, and an attenuation pole is generated on the transmission characteristics. For example, when the transmission characteristics are measured by mismatching the terminal impedance of this resonance combined type SAW filter, as shown in FIG. 2A, three resonance peaks (Fb
3, Fa3, Fa2) and the presence of an attenuation pole at the position indicated by the arrow near Fa1 (= Fb1). When the terminating impedance of this resonance combined type SAW filter is set to an appropriate value, FIG.
As shown in FIG. As is clear from FIG. 2 (a), the pass band is substantially from the resonance frequency Fb3 to Fa2, and the attenuation pole is formed on the high band side of the pass band. It is possible to realize. The solid line shown in FIG. 3 is an example of the filtering characteristic of the first embodiment of the present invention, and the broken line is an example of the filtering characteristic of the conventional configuration. The conventional resonance combining type SAW filter has a center frequency F ₀ (= 246 MHz) +0.2 MH
While the attenuation is 5 dB at z, the first
It can be seen that in the example of (1), an attenuation of 20 dB is obtained at F ₀ (= 246 MHz) +0.2 MHz, and the attenuation gradient is greatly improved on the high frequency side.

FIG. 4 shows a second embodiment of the present invention using the electrode pattern of FIG. 1A. FIG. 4A shows transmission characteristics and phase when the terminal impedance of the filter A is mismatched. FIG. 4B shows transmission characteristics and phase characteristics when the terminal impedance of the filter B is mismatched. In this embodiment, the phase of the electrode of the filter A and the phase of the electrode of the filter B are set to be opposite to each other. Then, the resonance frequency Fa1 of the A1 mode (0 °) of the filter A is made substantially equal to the resonance frequency Fb1 of the B1 mode (180 °) of the filter B. Further, the frequency relationship between the other modes of the filter A and the filter B is shown in FIG.
(B) The resonance frequencies Fb2 and Fb3 of the filter B are not matched with each other as shown in FIG.
a2 and Fa3 are arranged. That is, the relationship between the resonance frequencies of the filters A and B is set to Fb3 <Fa3 <Fa2 <Fb2. When the terminal impedance of the resonance combined type SAW filter configured by electrically connecting the filters A and B having such a frequency arrangement in parallel is mismatched, FIG.
Four resonance peaks appear as shown in FIG. Furthermore,
A frequency Fa whose phases are opposite to each other and whose resonance frequencies are substantially equal.
At 1 (= Fb1), an attenuation pole occurs. FIG.
(D) shows the filtering characteristics when the resonance combining type SAW filter is appropriately terminated, and a filter having a sharp cutoff characteristic on the high frequency side of the pass band can be realized.

FIG. 5 shows a third embodiment using the electrode pattern of FIG. 1A according to the present invention, wherein the phases of the electrodes of the filter A and the filter B are set to be opposite to each other. Further, the resonance frequency relation of each mode of the filter A and the filter B is arranged as shown in FIGS. 5 (a) and 5 (b). That is, the resonance frequency Fa2 of the A2 mode of the filter A and the B
The resonance frequency Fb1 of one mode is substantially equal to
Mode resonance frequency Fa3 and B3 mode resonance frequency F
b3 is set substantially equal. With the above setting, the resonance frequency Fb2 of the filter B in the B2 mode is arranged between the resonance frequencies Fa2 and Fa3 of the filter A. When the filter A and the filter B are electrically connected in parallel to form a resonance-combined SAW filter and the terminal impedances are mismatched, the transmission characteristics thereof become three resonance peaks and positions indicated by arrows as shown in FIG. , An attenuation pole occurs. When an appropriate terminal impedance is applied to the filter, a filter having a steep attenuation slope on the low frequency side having a pass band from Fb2 to Fa1 can be obtained as shown in FIG.

FIG. 6A is a schematic plan view of an electrode pattern showing a fourth embodiment according to the present invention.
IDTs 6a, 6b, 6c and reflectors 7a, 7
b, and a longitudinally coupled triple mode SAW filter B (filter B) composed of IDTs 8a, 8b, 8c and reflectors 9a, 9b is disposed. . When the electrode pattern as shown in FIG. 6A is formed, the phases of the filter A and the filter B are in phase. Here, a case is considered in which filters A and B are electrically connected in parallel to form a resonance-combined SAW filter. FIG. 6B shows the transmission characteristics and phase characteristics when the terminal impedance of the filter A is mismatched, and FIG. 6C shows the transmission characteristics and phase characteristics when the terminal resistance of the filter B is mismatched. FIG.
As shown in (b) and (c), A1 (primary) of filter A
Mode resonance frequency Fa1 and filter B B1 (primary)
The resonance frequencies of the resonance modes of the modes are substantially matched. A3 mode resonance frequency Fa3 of filter A and filter B
B2 mode resonance frequency Fb2 is made substantially equal. Further, the filter A and the filter B are electrically connected in parallel to form a resonance-combined SAW filter, and when the terminal impedance of the filter is mismatched, the transmission characteristics and phase characteristics of FIG. 7A are obtained. When the filter is appropriately terminated, the resonance frequency of the A3 mode and the resonance frequency of the B2 mode are substantially equal and the phases are opposite to each other as shown in FIG. 7B, so that the frequency of Fa3 (= Fb2) is reduced. An attenuation pole is generated, the passband is from Fa2 to Fa1 (= Fb1), and a filter having a steep attenuation slope on the lower side of the passband can be obtained.

FIG. 8 shows a fifth embodiment according to the present invention.
Two laterally coupled dual mode SAW filters (Filter A,
B) The present invention relates to a resonance combined type SAW filter configured by connecting in parallel. The electrode fingers of the IDT are shifted by λ / 2 so that the phases of the filter A and the filter B are opposite to each other.
As shown in (a), A1 (primary), A2 of filter A
The resonance frequencies of the (secondary) mode are Fa1 and Fa2.
Similarly, as shown in FIG. 9B, B1 (1
Next, the resonance frequencies of the B2 (secondary) mode are represented by Fb1 and Fb.
Let it be 2. Here, the resonance frequency Fa2 of the A2 mode of the filter A and the resonance frequency Fb2 of the B2 mode of the filter B are set substantially equal. According to the setting conditions of the IDT, the phases of the above two modes are opposite to each other. FIG. 9C shows transmission characteristics and phase characteristics when the terminal impedance of the resonance-coupling type SAW filter configured by electrically connecting the filter A and the filter B in parallel is different, and shows two resonance peaks and a frequency Fa2. An attenuation pole indicated by an arrow is generated at (= Fb2). FIG. 9D shows the filtering characteristics when an appropriate termination condition is applied to the filter, and the passband ranges from Fb1 to Fa.
Up to 1. As shown in FIGS. 9C and 9D, an attenuation pole indicated by an arrow is generated in the resonance frequency Fa2 (Fb2) on the lower side of the passband because the resonance frequency Fa2 in the A2 mode and the resonance frequency in the B2 mode are different from each other. This is because the flowing currents cancel each other out because the phases are almost equal and opposite to each other.
By using this means, it is possible to realize a filter having a steep attenuation slope on the lower side of the pass band as shown in FIG.

FIG. 10 shows a sixth embodiment according to the present invention. FIG. 10A is a diagram showing a frequency arrangement and a phase of a longitudinally coupled triple mode SAW filter (filter A), and FIG. 10B is a view showing a frequency arrangement and a phase of a longitudinally coupled dual mode SAW filter (filter B). FIG. The IDT is arranged such that the resonance frequency Fa1 of the A1 (first-order) mode of the filter A and the resonance frequency Fb1 of the B1 (first-order) mode of the filter B are substantially the same, and the phases of the first-order modes are in phase. . Further, the resonance frequency Fa3 of the A3 (tertiary) mode of the filter A and the resonance frequency Fb2 of the B2 (secondary) mode of the filter B are set substantially equal. The phase of the A3 mode is 0 °, and the phase of the B2 mode is 180 °.
And the phases are opposite to each other. Filter A set in this way
And filter B are electrically connected in parallel to each other to form a resonance-combined SAW
When the terminal impedance of the filter is mismatched, the transmission characteristics and the phase characteristics shown in FIG. Since the A3 mode and the B2 mode have substantially the same resonance frequency and opposite phases, an attenuation pole can be generated on the lower side of the passband as shown by the arrow in FIG. With appropriate termination of the filter,
As a result, a filter having the filtering characteristic shown in (d) can be obtained, and a filter having a steep attenuation gradient on the lower side of the pass band can be realized.

FIG. 11 is a view showing a frequency arrangement, a phase relationship and a filtering characteristic of a seventh embodiment using the electrode pattern shown in FIG. 1A according to the present invention. FIG. 11A shows transmission characteristics in which the terminating resistance of a longitudinally coupled triple mode SAW filter (filter A) is mismatched, and shows the resonance frequencies of A1 to A3 modes of the filter A and their phases. FIG. 11B shows a longitudinally coupled triple mode SAW filter (filter B) in which an IDT is set so as to have a phase opposite to that of the filter A.
, And shows the resonance frequency and the phase of the filter B from the B1 mode to the B3 mode. The corresponding resonance frequencies of the A1 and A3 modes of the filter A and the B1 and B3 modes of the filter B are set substantially equal, and the phase relation of each mode is set to be opposite to each other by setting the IDT. . When filters A and B are electrically connected in parallel to form a resonance-combined SAW filter, and the terminal impedance of the filter is mismatched, the transmission characteristics shown in FIG. 11C are obtained, and the attenuation poles are formed at Fa3 and Fa1. Characteristics. If the filter is appropriately terminated, the passband is from Fa2 to Fb2 as shown in FIG. 11D, and a filter having a steep attenuation characteristic in the low band side and the high band side can be realized.

If the first to seventh embodiments described above are used, the number of cascaded stages can be reduced. Therefore, a reactance element between stages required in a conventional multistage cascade connection configuration is used. It is possible to realize a filter having the same characteristics without using the filter. According to the present invention, the frequency at which the attenuation pole is generated can be easily controlled, so that the degree of freedom in design is greatly expanded. Further, if the filter according to the present invention is cascaded in multiple stages as shown in FIG. 12, it is possible to realize a steeper filter, so that the number of reactance elements X required between stages can be reduced as compared with the conventional configuration. it can.

As described above, the vertical coupling type SAW filter has been mainly described as an example of the two SAW resonator filters used in the present invention. However, the present invention is not limited to this, and FIGS. Also, the present invention can be applied to a case where the filter A and the filter B are laterally coupled SAW resonator filters as shown in FIG. 14 and a case where the filter A and the filter B are two-dimensional mode coupled SAW resonator filters as shown in FIG. Further, the present invention can be similarly applied to a SAW resonator filter having different types of filters A and B as in the case where the filter A is a longitudinally coupled SAW resonator filter and the filter B is a horizontally coupled SAW resonator filter. Further, it goes without saying that the present invention can be similarly applied to a balanced input / output type SAW filter.

[0019]

Since the present invention is configured as described above, it is possible to realize a SAW filter having a much better attenuation gradient than a conventional resonance combined type SAW filter. The requirements of the filter can be sufficiently satisfied. Furthermore, the characteristics that were conventionally connected in cascade in order to make the attenuation gradient steep can be realized with a filter having a small number of stages, and the insertion loss can be significantly reduced.

[Brief description of the drawings]

FIG. 1A is a schematic plan view of an electrode pattern according to an embodiment of a resonance synthesis type SAW filter according to the present invention.
(B), (c) is a figure which shows each resonance frequency arrangement | sequence of filter A and B, and a phase relationship.

2A is a diagram illustrating a frequency arrangement and a phase relationship of a resonance-combined SAW filter, and FIG. 2B is a diagram illustrating a filtering characteristic.

FIG. 3 is a solid line showing the filtering characteristics of the first embodiment according to the present invention;
A dashed line is an example of a conventional filtering characteristic for comparison.

FIGS. 4A and 4B show a filter A according to a second embodiment;
B shows the frequency arrangement and phase relationship, and (c) and (d) show the transmission characteristics and the filtering characteristics of the resonance combined type SAW filter.

FIGS. 5A and 5B show a filter A according to a third embodiment;
B shows the frequency arrangement and phase relationship, and (c) and (d) show the transmission characteristics and the filtering characteristics of the resonance-combined SAW filter.

6A is a schematic plan view of an electrode pattern according to a fourth embodiment of the present invention, FIG. 6B and FIG.
FIG. 6 is a diagram showing the respective resonance frequency arrangements and phase relationships of B.

FIGS. 7A and 7B are diagrams illustrating a transmission characteristic and a filtering characteristic of a resonance combined type SAW filter according to a fourth embodiment of the present invention.

FIG. 8 is a schematic plan view of an electrode pattern of a resonance combined type SAW filter in which two transversely coupled dual mode filters are connected in parallel.

9 (a) and 9 (b) are diagrams showing respective resonance frequency arrays and phase relationships of filters A and B in the fifth embodiment of the present invention, and FIGS. 9 (c) and 9 (d) are resonance composite type. FIG. 3 is a diagram illustrating transmission characteristics and filtering characteristics of a SAW filter.

10 (a) and 10 (b) are diagrams showing the respective resonance frequency arrangements and phase relationships of filters A and B in the sixth embodiment of the present invention, and FIGS. FIG. 3 is a diagram illustrating transmission characteristics and filtering characteristics of a SAW filter.

11A and 11B are diagrams showing resonance frequency arrangements and phase relationships of filters A and B in the seventh embodiment of the present invention, and FIGS. 11C and 11D are resonance combination types. FIG. 3 is a diagram illustrating transmission characteristics and filtering characteristics of a SAW filter.

FIG. 12 shows a two-cascade connection resonance combined SAW according to the present invention.
It is a figure showing a filter.

FIG. 13 is an example of a resonance-combined SAW filter configured using a laterally coupled dual-mode SAW filter.

FIG. 14 is an example of a resonance-combined SAW filter configured using a laterally coupled triple mode SAW filter.

FIG. 15 is a view showing an electrode pattern of a two-dimensional mode-coupled SAW filter in which filters A and B are provided.

FIG. 16 shows a conventional resonance-combination type SAW filter, (a).
Is a diagram showing a schematic electrode pattern, (b) and (c) are diagrams showing a frequency arrangement and a phase relationship of filters A and B, respectively.
(D) is a diagram illustrating the transmission characteristics of the resonance-combined SAW filter.

FIG. 17 is a diagram showing a filtering characteristic α and a delay characteristic β of a resonance combined type SAW filter in which two longitudinally coupled triple mode filters are connected in parallel.

[Explanation of symbols]

1. Piezoelectric substrates 2a, 2b, 2c, 4a, 4b, 4c,
6a, 6b, 6c IDT 8a, 8b, 8c IDT 3a, 3b, 5a, 5b, 7a, 7b, 9a, 9b
Reflector Fa1 Resonant frequency of the first-order mode of filter A Fa2 Resonant frequency of the second-order mode of filter A Fa3 Resonant frequency of the third-order mode of filter A Fb1 Resonant frequency of the first-order mode of filter B Fb2: Resonance frequency of second-order mode of filter B Fb3: Resonance frequency of third-order mode of filter B 0 °, 180 ° -mode phase X: Reactance element

Claims (9)

[Claims] 1. At least two coupled multimode SAW filters each having at least two IDTs disposed on a piezoelectric substrate and a reflector on the outermost side thereof and utilizing acoustic coupling of a surface wave to be excited. In a resonance combined type SAW filter electrically connected in parallel, at least one of the vibration modes of one of the coupled multi-mode SAW filters and the vibration mode of the other multi-mode SAW filter. At least one
And the resonance frequency is equal to each other, and the phase shift amount between the input and output at the resonance frequency is (2n + 1) π (n =
0, 1,...) Which are different from each other. 2. The polarized surface acoustic wave filter according to claim 1, wherein the multi-mode SAW filter is a longitudinally-coupled multi-mode SAW filter. 3. A longitudinal coupling in which the multi-mode SAW filter is formed by arranging an input / output IDT on a piezoelectric substrate along a propagation direction of a surface acoustic wave and reflectors on both sides thereof and arranging a grating between the input / output IDTs. 2. The polarized surface acoustic wave filter according to claim 1, wherein the surface acoustic wave filter is a multi-mode SAW filter. 4. The polarized surface acoustic wave filter according to claim 1, wherein the multi-mode SAW filter is a transversely coupled multi-mode SAW filter. 5. The multi-mode SAW filter, wherein the multi-mode SAW filter is a two-dimensional mode-coupled multi-mode SAW filter combining longitudinal mode resonance utilizing coupling in the propagation direction of a surface wave and transverse mode resonance perpendicular to the propagation direction. The polarized surface acoustic wave filter according to claim 1, wherein: 6. The polarized surface acoustic wave filter according to claim 1, wherein one of the multimode SAW resonator filters is a longitudinally coupled multimode SAW filter and the other is a laterally coupled multimode SAW filter. 7. The polarized surface acoustic wave filter according to claim 1, wherein one of the multimode SAW filters is a longitudinally coupled multimode SAW filter and the other is a two-dimensional mode coupled multimode SAW filter. 8. The polarized surface acoustic wave filter according to claim 1, wherein one of the multi-mode SAW filters is a laterally coupled multi-mode SAW filter and the other is a two-dimensional mode coupled multi-mode SAW filter. 9. A polarized surface acoustic wave filter comprising a cascade configuration using at least one polarized surface acoustic wave filter according to claim 1.