JPH10270982A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently secure attenuation quantity out of a band with a low loss by providing plural resonator filters containing a first resonator-type filter, a second resonator filter whose structure differs from the first resonator-type filter and a means connecting the resonator filters on a piezoelectric substrate. SOLUTION: The electrode of the surface acoustic wave filter is constituted by connecting two types of resonator-type filters, 2IDT (interdigital transducers) filters 1 and 2, for example, to the piezoelectric substrate. The first 2IDT filter 1 has two IDT 3 and 4 arranged by leaving a prescribed interval and two Gr (grating-like reflectors) 5 and 6 arranged so that they sandwich them. The second 2IDT filter 2 has two IDT7 and 8 and two Gr9 and 10 arranged so as to sandwich them. IDT4 and IDT7 are connected through a connection line 11.

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 a mobile communication device such as a mobile phone.

[0002]

2. Description of the Related Art In recent years, the field of mobile communication has been remarkably developed, and various systems have been developed. With the downsizing of communication devices used in these systems, downsizing of electronic components used is also required.

A surface acoustic wave filter has features such as small size, light weight, high reliability, and excellent out-of-band attenuation characteristics.
In recent years, it has been actively used in the mobile communication field. Further, since the filter characteristics determine the performance of the communication device, the surface acoustic wave filter having excellent frequency characteristics is now a key device of mobile communication devices.

[0004] However, the surface acoustic wave filter has a problem that insertion loss is large due to an operation principle of once converting an electric signal into mechanical energy called surface acoustic wave and then converting it into an electric signal again. Various methods are being studied in order to realize a low loss that can be used for a required filter for mobile communication equipment. For example, a one-way filter or a plurality of interdigital converters (@nter Digital Tran
sducer: hereinafter referred to as IDT) II
There are a DT method, a resonator type filter using resonance characteristics, a ladder type filter in which one-port type resonators are combined in a ladder shape, and the like.

[0005]

However, all of these filter systems have drawbacks.

For example, the one-way filter and the IIDT method can easily obtain complicated filter characteristics, but the insertion loss is worse than that using a resonance characteristic described later.
Since the size tends to be large, it is not suitable in the mobile communication field where low loss and small size are required.

Although a resonator type filter and a ladder type filter utilizing resonance characteristics can be easily reduced in size and reduced in loss, the filter characteristics are based on a grating-like reflector ( (Hereinafter referred to as Gr) and the number of comb-shaped electrode fingers constituting the IDT, which has a drawback that a complicated filter characteristic cannot be obtained.

Further, in the field of mobile communications, in addition to low loss, out-of-band attenuation is also required. Conventionally, the same filter is connected in multiple stages to secure out-of-band attenuation. In other words, there is a trade-off relationship that the tendency that a complicated filter characteristic cannot be obtained becomes strong, and a filter satisfying in all aspects has not been obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and provides a surface acoustic wave filter capable of securing a sufficient amount of out-of-band attenuation with low loss and obtaining complicated filter characteristics. It is intended to be.

An object of the present invention is to provide a surface acoustic wave filter having a high degree of design freedom.

[0011]

According to a first aspect of the present invention, there is provided a surface acoustic wave filter comprising: a piezoelectric substrate; a first resonator type filter formed on the piezoelectric substrate; It comprises a plurality of resonator filters including a second resonator filter having a different structure from the first resonator filter, and means for connecting the resonator filters.

A surface acoustic wave filter according to a second aspect is characterized in that the plurality of resonator type filters have different numbers of interdigital converters.

According to a third aspect of the present invention, there is provided a surface acoustic wave filter according to the above-mentioned filter, wherein the filter has three or more resonator filters, and the resonator filter has a signal input and the resonator filter has a signal input. The number of interdigital converters is two or more.

According to a fourth aspect of the present invention, there is provided a surface acoustic wave filter according to the above-mentioned filter, wherein the filter comprises a plurality of resonator-type filters having the same number of a plurality of inter-digital converters. Wherein at least one of the interdigital converters has the same structure and each resonator type filter has a different frequency characteristic.

According to a fifth aspect of the present invention, there is provided a surface acoustic wave filter having two or more resonator type filters formed on a piezoelectric substrate, the first surface acoustic wave filter having two or more interdigital converters. A resonator type filter; and a second resonator type filter having at least two interdigital converters, wherein at least one interdigital converter has a structure different from that of the first resonator type filter. I do.

A surface acoustic wave filter according to a sixth aspect of the present invention is a surface acoustic wave filter having two or more resonator-type filters formed on a piezoelectric substrate, wherein the first resonator has a plurality of interdigital converters. A secondary filter and the same number of interdigital converters as the first resonator type filter, the number being the same as that of the first resonator type filter, wherein at least one of the interdigital converters is the first digital filter. It has the same structure as at least one interdigital converter of the resonator filter, and includes at least a second resonator filter having a frequency characteristic different from that of the first resonator filter.

A surface acoustic wave filter according to a seventh aspect of the present invention is a surface acoustic wave filter in which three or more resonator filters are formed on a piezoelectric substrate, wherein the first resonator filter and the first resonator filter are provided. The second structure is different from the resonator type filter
And a third resonator, which is interposed between the first resonator type filter and the second resonator type filter, and has a different structure from the first and second resonator type filters. A resonator-type filter.

The surface acoustic wave filter according to the present invention is a surface acoustic wave filter in which three or more resonator type filters are formed on a piezoelectric substrate, the first surface acoustic wave filter having one or more interdigital converters. , A second resonator type filter having the same number of interdigital converters as the first resonator type filter, the first resonator type filter and the second resonator type filter And a third resonator-type filter having a different number of interdigital converters from the first and second resonator-type filters.

A surface acoustic wave filter according to a ninth aspect is a surface acoustic wave filter in which three or more resonator type filters are formed on a piezoelectric substrate, the first surface acoustic wave filter having one or more interdigital converters. A second resonator-type filter having a different number of interdigital converters from the first resonator-type filter;
A third resonator type filter interposed between the resonator type filter and the second resonator type filter and having a different number of interdigital converters from the first and second resonator type filters; and Is provided.

The surface acoustic wave filter according to claim 10 is
A surface acoustic wave filter in which two or more resonator filters are formed on a piezoelectric substrate, wherein the plurality of resonator filters have substantially the same pass band amplitude characteristics but different attenuation band amplitude characteristics. Means for synthesizing the amplitude characteristic of the resonator type filter.

The surface acoustic wave filter according to claim 11 is
A surface acoustic wave filter having two or more resonator-type filters formed on a piezoelectric substrate, having a predetermined passband amplitude characteristic, and having a higher attenuation band or a lower attenuation band than this passband. One of them has a first resonator type filter having a gradual slope attenuation amplitude characteristic, and the other has a passband amplitude characteristic substantially the same as that of the first resonator type filter. It has a second resonator type filter having a sharp slope attenuation amplitude characteristic on the attenuation band side having a slope attenuation amplitude characteristic, and means for combining the amplitude characteristics of these resonator type filters.

The surface acoustic wave filter according to claim 12 is
A surface acoustic wave filter in which two or more resonator type filters are formed on a piezoelectric substrate, having a predetermined passband amplitude characteristic, and having one of a high band side and a low band side near the passband. A first resonator type filter having an anti-resonance point, having substantially the same pass band amplitude characteristic as the first resonator type filter, and having an anti-resonance point of the first resonator type filter and this pass band amplitude It has a second resonator type filter having an anti-resonance point symmetrical with respect to the center frequency of the characteristic, and means for synthesizing the amplitude characteristics of these resonator type filters.

Here, the resonator type filter can include an interdigital converter (IDT) and a grating-like reflector (Gr). IDT is
For example, a comb-shaped electrode made of a metal thin film crosses each other. Usually, two metal-film grating-like reflectors (Gr) are arranged so as to sandwich ΔDT along the propagation direction of the surface acoustic wave excited by the IDT.

In a resonator type surface acoustic wave filter having Gr outside the IDT, a surface acoustic wave having frequency characteristics generated by excitation of the IDT has a surface acoustic wave having a frequency (wavelength) corresponding to the periodicity of Gr. Since the surface wave is reflected and excited by Gr, the energy of the surface acoustic wave at this frequency (wavelength) can be theoretically all extracted as an output signal, so that a filter having a small insertion loss can be formed. is there.

However, since the frequency characteristic is obtained by multiplying the fundamental IDT sinX / X type excitation characteristic by the Gr reflection characteristic, the attenuation characteristic is determined by the IDT.
The pass band is uniquely determined by Gr. The parameters directly controlling these characteristics are the mechanical coupling coefficient of the piezoelectric substrate, the number of comb-shaped electrode fingers constituting the IDT, and the reflectance determined by the substrate in the case of Gr. Yes, these can be controlled to obtain desired characteristics.However, since the surface acoustic wave filter, which is a passive component, is subject to restrictions such as impedance and size due to an external circuit, design parameters are actually limited. Therefore, the degree of freedom in design was small.

In order to obtain more out-of-band attenuation, the same resonator filter has conventionally been cascaded in multiple stages.
In order to realize a low-loss filter, it is necessary to perform image joining in the passband, that is, to select a resonator filter with zero susceptance at the joint surface of the filter. I was That is, in the present invention, since resonator-type filters having different frequency characteristics are connected, more complicated characteristics can be realized than a conventional filter in which the same filters are cascaded. In addition, the image junction, which is a necessary condition for reducing the loss, is limited to a filter having the least area where the susceptance is zero, but if this resonator type filter is selected to have a minimum required in the pass band, There is no problem in reducing the loss.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an electrode pattern of a surface acoustic wave filter according to one embodiment of the present invention. These electrodes are formed on a piezoelectric substrate, for example, a 45 ° X-cut LBO substrate. This surface acoustic wave filter is configured by connecting two types of resonator type filters, for example, 2IDT filters 1 and 2. Thus, a 600Ω-based surface acoustic wave filter is formed. Here, the first 2IDT filter 1 is composed of two IDTs arranged at a predetermined interval.
3, 4 and two Gr arranged to sandwich them.
5 and 6. Similarly, the second 2IDT filter 2 has two IDTs 7 and 8 arranged at a predetermined interval.
And two Gr9, 10 arranged so as to sandwich them.
And The IDT 4 of the first 2IDT filter 1 and the IDT 7 of the second 2IDT filter 2 are connected via a connection line 11. The IDT 3 of the first 2IDT filter 1 and the IDT 8 of the second 2IDT filter 2 have exactly the same structure.
4 and the IDT 7 of the second 2IDT filter 2 have different structures. Thereby, the frequency characteristic of the first 2IDT filter 1 and the frequency characteristic of the second 2IDT filter 2 are different.

FIG. 2 shows the characteristics of each resonator type filter as Smi.
This is a simulation using an equivalent circuit of th. 12 is a 2IDT filter 1 alone, 13 is a 2IDT filter
FIG. 9 is a characteristic diagram of the filter 2 alone. FIG. 3 shows a simulation result of a combination of the two 2IDT filters 1 and 2.

FIG. 4 is a frequency characteristic diagram when the actually obtained surface acoustic wave filter is measured by a circuit adjusted to 600Ω by a capacitor and a coil. The result of the actual product and the simulation result were very similar, confirming the effectiveness of the present invention.

Next, a second embodiment of the present invention will be described.

FIG. 5 is a view showing an electrode pattern of a surface acoustic wave filter according to a second embodiment of the present invention. These electrodes are formed on a piezoelectric substrate, for example, a 64 ° Y-cut LNB substrate. This surface acoustic wave filter is a 50 Ω system composed of two resonator-type filters, for example, 3IDT filters 14 and 15, and one resonator-type filter disposed between the 3IDT filters 14 and 15, for example, 1 IDT filter 16. Filter. The 3IDT filter 14 has three IDTs 17, 18, and 19 and two G
r20 and r21. 3IDT filter 15 is 3
IDTs 22, 23 and 24 and two Gr sandwiching them
25 and 26. 3IDT filters 14 and 3I
The DT filter 15 has the same configuration and the same frequency characteristics. The 1 IDT filter 16 includes one IDT 27 and two Gr 28 and 29 sandwiching the IDT 27. 1I
The DT filter 16 has a different configuration from the 3IDT filters 14 and 15 and has different frequency characteristics. IDT 17 of 3IDT filter 14 and IDT of 1IDT filter 16
27 is connected via a connection line 30. 3ID
The IDT 19 of the T filter 14 and the IDT 27 of the 1 IDT filter 16 are connected via a connection line 31.
The IDT 22 of the 3IDT filter 15 and the IDT 27 of the 1IDT filter 16 are connected via a connection line 32. The IDT 24 of the 3IDT filter 15 and the IDT 27 of the 1IDT filter 16 are connected via a connection line 33.

FIG. 6 shows the characteristics of each resonator type filter as Smi.
This is a simulation using an equivalent circuit of th. 34 is a 3IDT filter 14, 15 alone, 35 is 1
FIG. 9 is a characteristic diagram of the IDT filter unit 16. As can be seen from FIG. 6, in the case of the present embodiment, since the amplitude characteristic of the 3IDT filter is not symmetric with respect to the center frequency, the surface acoustic wave filter obtained by combining the anti-resonance points of the 1IDT filter is symmetric with respect to the center frequency. It was set to attenuate with a slope.

FIG. 7 shows a simulation result of a combination of three resonator type filters set as described above.

FIG. 8 is a frequency characteristic diagram of a surface acoustic wave filter actually obtained. In this way, the simulation results are very similar to the real ones. Further, FIG. 9 shows a frequency characteristic diagram of a surface acoustic wave filter according to the prior art, which is composed of only two identical 3IDT filters without having 1 IDT, as a comparison with the present embodiment. Thus, the effectiveness of the present invention can be clearly understood.

Next, a third embodiment of the present invention will be described.

FIG. 10 is a view showing an electrode pattern of a surface acoustic wave filter according to a third embodiment of the present invention. These electrodes are made of a piezoelectric substrate, for example, a 36 ° Y-cut LTA.
Substrate Formed on the substrate. This surface acoustic wave filter has 2
Resonator type filters, for example, a 3IDT filter 36,
The 2IDT filter 37 and the 3IDT filters 36, 2
One resonator type filter disposed between the IDT filters 37, for example, a 100Ω-system filter including one IDT filter 38. The 3IDT filter 36 has three IDs
T39, 40, 41 and two Gr42, 4 sandwiching them
3 The 2IDT filter 37 has two IDTs.
44 and 45 and two Gr 46 and 47 sandwiching them. 3IDT filter 14 and 3IDT filter 15
Has a different configuration and different frequency characteristics. 1I
The DT filter 38 is composed of one IDT 48 and two
Gr49 and 50. 1 IDT filter 3
8 has a different configuration from the 3IDT filter 36 and the 2IDT filter 37, and has different frequency characteristics. IDT 39 of 3IDT filter 36 and ID of 1IDT filter 38
It is connected to T48 via a connection line 51. 3I
IDT 41 of DT filter 36 and 1 IDT filter 38
Is connected to the IDT 48 via a connection line 52. The IDT 44 of the 2IDT filter 37 and the IDT 48 of the 1IDT filter 38 are connected via a connection line 53.

FIG. 11 shows the characteristics of each resonator type filter as Sm.
This is a simulation performed using an equivalent circuit of "is". 54 is a characteristic diagram of the 3IDT filter 36, 55 is a characteristic diagram of the 1IDT filter 38, and 56 is a characteristic diagram of the 2IDT filter 37 alone. As can be seen from FIG. 11, in the case of this embodiment, 2
The logarithm of the comb-shaped electrode fingers constituting the IDT of each filter was adjusted so that the peaks and valleys of the amplitude characteristics of the IDT filter 37 and the 3IDT filter 36 were reversed. Also, the 1 IDT filter 38 has an anti-resonance point 58 whose center frequency is 3 IDT
The filter was set to be symmetric with the trap 57 of the filter.

FIG. 12 shows a simulation result of a combination of the three resonator filters 36, 37, and 38 set as described above.

FIG. 13 is a frequency characteristic diagram when the actually obtained surface acoustic wave filter is measured by a circuit adjusted to 100Ω by a capacitor and a coil. In this way, the simulation results are very similar to the real ones,
The effectiveness of the present invention is understood.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the technical concept of the present invention.

For example, in the surface acoustic wave filter according to the embodiment shown in FIG. 1, two kinds of 2IDT filters 1 and 2 are connected. It is also possible to insert an IDT filter. That is, for example, 2IDT filter-1ID
Various combinations are possible within the scope of the present invention, such as a T filter-1 IDT filter-2 IDT filter.

In the above-described embodiments, the 45 ° X-cut LBO substrate, the 64 ° Y-cut LNB substrate, and the 36 ° Y-cut LTA substrate have been described as examples of the piezoelectric substrate. However, it is needless to say that a piezoelectric substrate of another material can be used.

[0044]

As described above, according to the present invention,
A sufficient amount of out-of-band attenuation can be secured with low loss, and a complicated filter characteristic can be obtained. Further, the degree of freedom in designing the surface acoustic wave filter can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an electrode pattern of a surface acoustic wave filter according to a first embodiment of the present invention.

FIG. 2 is a simulation result of each resonator type filter alone shown in FIG. 1;

FIG. 3 is a simulation result of the surface acoustic wave filter of FIG. 1;

FIG. 4 is a diagram illustrating characteristics of the surface acoustic wave filter of FIG. 1;

FIG. 5 is a diagram showing an electrode pattern of a surface acoustic wave filter according to a second embodiment of the present invention.

6 is a simulation result of each resonator type filter of FIG. 5 alone.

7 is a simulation result of the surface acoustic wave filter of FIG.

FIG. 8 is a diagram illustrating characteristics of the surface acoustic wave filter of FIG. 5;

FIG. 9 is a diagram illustrating characteristics of a surface acoustic wave filter obtained by a conventional technique.

FIG. 10 is a diagram showing an electrode pattern of a surface acoustic wave filter according to a third embodiment of the present invention.

11 is a simulation result of each resonator type filter of FIG. 10 alone.

12 is a simulation result of the surface acoustic wave filter of FIG.

FIG. 13 is a diagram illustrating characteristics of the surface acoustic wave filter of FIG. 10;

[Explanation of symbols]

 1, 2, 2 IDT filter 3, 4, 7, 8 IDT 5, 6, 9, 10 Gr 11 connection line

Claims (12)

[Claims] 1. A plurality of piezoelectric substrates each including a piezoelectric substrate, a first resonator filter formed on the piezoelectric substrate, and a second resonator filter having a structure different from that of the first resonator filter. A surface acoustic wave filter comprising: a resonator type filter; and means for connecting the resonator type filter. 2. The surface acoustic wave filter according to claim 1, wherein the number of interdigital converters included in the plurality of resonator filters is different. 3. The method according to claim 1, wherein the number of interdigital converters included in the resonator type filter having three or more resonator type filters and receiving a signal input and the number of interdigital converters included in the resonator type filter receiving the signal input is two or more. The surface acoustic wave filter according to claim 1, wherein: 4. A plurality of resonator type filters having the same number of interdigital converters, wherein at least one of the interdigital converters of each resonator type filter has the same structure, 2. The surface acoustic wave filter according to claim 1, wherein frequency characteristics of the respective resonator filters are different. 5. A surface acoustic wave filter in which two or more resonator filters are formed on a piezoelectric substrate, the first resonator filter having two or more interdigital converters, and an interdigital conversion. A surface acoustic wave comprising at least two resonators, and at least one interdigital converter having a second resonator-type filter having a structure different from that of the first resonator-type filter. filter. 6. A surface acoustic wave filter in which two or more resonator filters are formed on a piezoelectric substrate, wherein the first resonator filter has a plurality of interdigital converters; A first resonator-type filter connected to the resonator-type filter and having the same number of inter-digital converters as at least one of the first resonator-type filters, wherein at least one inter-digital converter includes at least one inter-digital converter of the first resonator-type filter; Has the same structure as the interdigital converter,
A surface acoustic wave filter comprising at least a second resonator type filter having a different frequency characteristic from the first resonator type filter. 7. A surface acoustic wave filter in which three or more resonator filters are formed on a piezoelectric substrate, wherein the first resonator filter and the first resonator filter have a structure. A different second resonator type filter, interposed between the first resonator type filter and the second resonator type filter, and has a different structure from the first and second resonator type filters. A surface acoustic wave filter comprising a third resonator type filter. 8. A surface acoustic wave filter having three or more resonator filters formed on a piezoelectric substrate, the first resonator filter having one or more interdigital converters; A second resonator-type filter having the same number of interdigital converters as one resonator-type filter; and a second resonator-type filter interposed between the first resonator-type filter and the second resonator-type filter; A surface acoustic wave filter comprising: a first resonator filter, a second resonator filter, and a third resonator filter having a different number of interdigital converters. 9. A surface acoustic wave filter in which three or more resonator filters are formed on a piezoelectric substrate, the first resonator filter having one or more interdigital converters; A second resonator-type filter having a different number of interdigital converters from one resonator-type filter; and a second resonator-type filter interposed between the first resonator-type filter and the second resonator-type filter; A surface acoustic wave filter comprising: a first resonator filter, a second resonator filter, and a third resonator filter having a different number of interdigital converters. 10. A surface acoustic wave filter in which two or more resonator filters are formed on a piezoelectric substrate, wherein a plurality of resonators have substantially the same passband amplitude characteristics but different attenuation band amplitude characteristics. A surface acoustic wave filter comprising: a type filter; and means for synthesizing the amplitude characteristics of these resonator type filters. 11. A surface acoustic wave filter having two or more resonator-type filters formed on a piezoelectric substrate, having a predetermined passband amplitude characteristic, and a higher attenuation band or a lower attenuation band than the passband. A first resonator-type filter in which one of the band-side attenuation bands has a gentle slope attenuation amplitude characteristic; and a first resonator having substantially the same pass-band amplitude characteristic as the first resonator-type filter. A second resonator type filter having a sharp slope attenuation amplitude characteristic on the attenuation band side having a gentle slope attenuation amplitude characteristic in the type filter, and means for synthesizing the amplitude characteristics of these resonator type filters. A surface acoustic wave filter. 12. A surface acoustic wave filter having two or more resonator-type filters formed on a piezoelectric substrate, having a predetermined pass band amplitude characteristic, and a high band or a low band near the pass band. A first resonator-type filter having an anti-resonance point on one of its sides; having a passband amplitude characteristic substantially equal to that of the first resonator-type filter; And a second resonator type filter having an anti-resonance point symmetrical with respect to the center frequency of the pass band amplitude characteristic, and means for synthesizing the amplitude characteristic of the resonator type filter. filter.