JPH05129872A - Surface wave resonator, surface wave filter, branching filter and mobile radio equipment - Google Patents

Abstract

(57) [Summary] [Objective] To obtain a high-performance surface acoustic wave resonator, a surface acoustic wave filter, a demultiplexer, and a mobile radio device. [Structure] One interdigital electrode is arranged in the center, symmetrically arranged on both sides of the interdigital electrode, and a plurality of sets of interdigital electrodes electrically connected in parallel are used, and the interdigital electrode is connected in parallel with the central interdigital electrode. Each pair of interdigital electrodes is connected in series to form a one-terminal pair surface acoustic wave resonator, and the surface acoustic wave is gradually or stepwise from the center of the surface acoustic wave resonator to the outside of the surface acoustic wave propagation path. The weighting was such that the excitation intensity of the was weak. Capacitance of each of the interdigital electrodes connected in series is made substantially equal. A surface wave filter, a demultiplexer, and a mobile radio device using this resonator. [Effect] A surface acoustic wave resonator having a high electric impedance and a high resonance sharpness can be realized. It is possible to realize a compact and high-performance surface wave filter, demultiplexer and ultra-compact mobile radio device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface wave resonator formed on a piezoelectric substrate, a surface wave filter, a duplexer for mobile radio equipment,
And a mobile radio device.

[0002]

2. Description of the Related Art A conventional surface wave resonator is disclosed in, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Unexamined Patent Publication No. 0-65610, a plurality of interdigital electrodes connected in series is known. In addition, for example, the 1st to 7th materials of the 24th meeting of the 150th Committee of the Japan Society for the Promotion of Science Acoustic Wave Device Technology (October 1990)
The page has a description about weighting of surface wave resonators. A method of constructing a surface wave filter and a demultiplexer using a surface wave resonator is disclosed in, for example, JP-A-63-1.
No. 32515 is known.

[0003]

When a surface acoustic wave filter is constructed by using the surface acoustic wave resonator shown in the above-mentioned prior art, there are problems such as insufficient attenuation and large insertion loss.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to realize a compact surface wave filter having a small insertion loss in the pass band and a large attenuation in the stop band. Another object of the present invention is to realize a small and lightweight mobile radio device by configuring a small duplexer.

[0005]

In order to achieve the above object, according to the present invention, one terminal is constructed so that a plurality of interdigital electrodes are connected in series or in series / parallel to form one acoustic propagation path. In the anti-surface wave resonator, the weighting is performed so that the excitation intensity of the surface wave gradually becomes weaker gradually from the center of the surface wave resonator toward the outside of the acoustic propagation path. As the weighting method, the cross width weighting (apodization), the thinning method, or the resistance weighting method was used. A surface wave filter and a demultiplexer were constructed using these surface wave resonators. In addition, a mobile wireless device is configured using the surface wave filter and the demultiplexer described above.

[0006]

[Function] Since a plurality of interdigital electrodes are connected in series or series-parallel to form a surface wave resonator, the number of pairs of each interdigital electrode is changed or the connection method of each interdigital electrode is changed. The degree of freedom in designing the electric impedance characteristics of the wave resonator is large. In addition, since the weight is set so that the excitation intensity of the surface wave gradually weakens toward the outside from the center of the surface wave resonator, the acoustic propagation path end of the surface wave resonator is Since the energy of the surface wave leaking to the can be further reduced, the resonance sharpness can be increased. On the other hand, in a surface wave filter configured by combining surface wave resonators, a resonator having a large resonance sharpness and various impedance characteristics is required according to the performance of the filter. Therefore, a higher performance surface acoustic wave filter can be realized by forming a surface acoustic wave filter by combining the above surface acoustic wave resonators. Also, by using this surface wave filter, it is possible to realize an ultra-small size demultiplexer and a mobile radio device.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS.
Will be described. The surface acoustic wave resonator 2 shown in FIG. 1 uses the interdigital electrode 3 shown in FIG. 2, the interdigital electrode 4 shown in FIG. 3, and the interdigital electrode 5 shown in FIG. Are arranged in a lateral direction on the piezoelectric substrate 1 so as to have a shape. The distance between the interdigital electrodes, for example, the distance between the right end electrode finger of the interdigital electrode 3 and the left end electrode finger of the interdigital electrode 4 may be the same as the interval between the interdigital electrodes. Electrically, the interdigital electrodes 3 and 5 are connected in parallel, which is connected in series with the interdigital electrode 4,
The terminals 6 and 7 are connected to the outside. The surface wave resonator 2 is weighted by the apodization method so that the excitation intensity of the surface wave gradually becomes weaker from the center of the whole surface to the outside. In addition, each of the interdigital transducers 3, 4, and 5 is arranged such that the electrostatic capacitance of the interdigital transducer 4 and the combined value of the electrostatic capacitances of the interdigital electrodes 3 and 5 connected in parallel are substantially equal to each other. The index is set. With such a configuration, the electrical impedance of the conventional general surface acoustic wave resonator shown in FIG. 6 can be increased about four times as compared with the case where the total electrode index is almost the same. At the same time, by weighting the entire surface acoustic wave resonator 2, its resonance sharpness, particularly the resonance sharpness of the anti-resonance frequency, can be increased. Figure 6
In the general surface acoustic wave resonator shown in (1), if the electrode index is increased in order to increase the resonance sharpness at the resonance frequency, the capacitance also increases and the electrical impedance decreases.
Therefore, it is difficult to increase the electrical impedance at the anti-resonance frequency even if weighting is performed to increase the resonance sharpness at the anti-resonance frequency.

As described above, according to this embodiment, it is possible to realize a surface wave resonator having a high electric impedance and a large resonance sharpness. Further, even if the interdigital electrodes are arranged and connected as shown in FIG. 5, the same effect can be obtained.
Further, although one set of interdigital electrodes connected in parallel is used in this embodiment, the electrical impedance can be further increased by using plural sets of interdigital electrodes.

Next, a second embodiment of the present invention will be described with reference to FIGS. The surface acoustic wave resonator 12 shown in FIG.
Using the interdigital electrode 13 shown in FIG. 8, the interdigital electrode 14 shown in FIG. 9, and the interdigital electrode 15 shown in FIG. 10,
Piezoelectric substrate 1 so that these surface wave propagation paths are linear
It is configured by arranging in the horizontal direction on the top. The distance between the interdigital electrodes, for example, the distance between the right end electrode finger of the interdigital electrode 13 and the left end electrode finger of the interdigital electrode 14 may be the same as the interval between the interdigital electrodes. Electrically, the interdigital electrodes 13 and 15 are connected in parallel, which is connected in series with the interdigital electrode 14 and is externally connected at terminals 16 and 17. The surface acoustic wave resonator 12 is weighted by the thinning method so that the excitation intensity of the surface acoustic wave becomes gradually weaker toward the outside from the center of the whole surface acoustic wave resonator 12. Further, the electrostatic capacitance of the interdigital transducer 14 and the electrostatic capacitance of the interdigital electrodes 13 and 15 connected in parallel are approximately equal to each other.
The respective electrode indices of the interdigital electrodes 13, 14, 15 are set.

As described above, according to this embodiment, a surface acoustic wave resonator having a high electric impedance and a large resonance sharpness can be realized as in the first embodiment. Also,
The present embodiment has an advantage that the loss due to diffraction can be reduced. Even if the interdigital electrodes are arranged and connected as shown in FIG. 11, the same effect can be obtained.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 12 is a block diagram of a surface acoustic wave filter configured by combining surface acoustic wave resonators of the present invention. Figure 1,
5, 7 or the surface wave resonators 31, 32, 3 shown in FIG.
One electrode of 3, 34 is grounded, and the other electrodes are coupled by coupling elements 35, 36, 37 such as capacitors and inductors. 38, 39, 40, 41 are matching elements, which are set so as to match the characteristic impedance of the terminals 42, 43. This type of filter is disclosed, for example, in Japanese Patent Laid-Open No. 63-1.
As described in Japanese Patent No. 32515, the characteristics of the surface acoustic wave resonators 31, 32, 33, 34 and the values of the coupling elements 35, 36, 37 are determined according to the specifications of the filter. Since the surface wave resonators 31, 32, 33, and 34 of this embodiment have a large degree of freedom in designing the resonance impedance characteristic, it is possible to improve the performance and downsize the surface wave filter.

FIG. 13 is a block diagram showing another embodiment of the surface acoustic wave filter constructed by combining the surface acoustic wave resonators of the present invention. One electrode of the surface acoustic wave resonator 51, 52 shown in FIGS. 1, 5, 7 or 11 is grounded, and the other electrode is coupled by the surface acoustic wave resonator 53 shown in FIG. ing. 54, 55, 56 and 57 are matching elements, which are set so as to match the characteristic impedance of the terminals 58 and 59. This type of filter includes surface acoustic wave resonators 51, 52, 5
Since it is necessary to greatly change the resonance impedance characteristics of No. 3, it is more effective to use the surface wave resonator of the present invention shown in FIGS. Further, as shown in FIG. 14, by using the surface acoustic wave resonators of the present invention connected in series, the degree of freedom in designing the resonance impedance characteristics is further increased. In FIG. 14, 61, 62, 6
3, 64, 65 and 66 are surface acoustic wave resonators of the present invention, 67,
68, 69 and 70 are matching elements, and 71 and 72 are terminals. Further, in the embodiment of FIG. 12, FIG. 13 or FIG. 14, it may be combined with a conventional surface wave resonator.

[0013]

As described above, according to the present invention,
A surface acoustic wave resonator having a high electric impedance and a high resonance sharpness can be realized. Further, by forming a surface wave filter by combining these surface wave resonators, it is possible to realize a compact and high performance surface wave filter with a small insertion loss in the pass frequency band and a large attenuation in the stop frequency band. Also, by using this surface wave filter, it is possible to realize an ultra-small size demultiplexer and a mobile radio device.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a comb-shaped electrode used in the first embodiment of the present invention.

FIG. 3 is a diagram showing a comb-shaped electrode used in the first embodiment of the present invention.

FIG. 4 is a diagram showing a comb-shaped electrode used in the first embodiment of the present invention.

FIG. 5 is a diagram showing a second embodiment of the present invention.

FIG. 6 is a diagram showing a conventional example of a surface acoustic wave resonator.

FIG. 7 is a diagram showing a third embodiment of the present invention.

FIG. 8 is a diagram showing a comb-shaped electrode used in a third embodiment of the present invention.

FIG. 9 is a diagram showing a comb-shaped electrode used in a third embodiment of the present invention.

FIG. 10 is a diagram showing a comb-shaped electrode used in a third embodiment of the present invention.

FIG. 11 is a diagram showing a fourth embodiment of the present invention.

FIG. 12 is a block diagram showing an embodiment of the surface acoustic wave filter of the present invention.

FIG. 13 is a block diagram showing another embodiment of the surface acoustic wave filter of the present invention.

FIG. 14 is a block diagram showing another embodiment of the surface acoustic wave filter of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate 2 ... Surface wave resonator 3, 4, 5 ... Interdigital electrode 6, 7 ... Terminal 12 ... Surface wave resonator 13, 14, 15 ... Interdigital transducer Electrodes 16, 17 ... Terminals 31, 32, 33, 34 ... Surface wave resonators 35, 36, 37 ... Coupling elements 38, 39, 40, 41 ... Matching elements 42, 43 ... Terminals 51, 52, 53 ... Surface wave resonators 54, 55, 56, 57 ... Matching elements 58, 59 ... Terminals 61, 62, 63, 64, 65, 66 ... Surface wave resonators , 67, 68, 69, 70 ... Matching element 71, 72 ... Terminal

Claims (8)

[Claims] 1. A single interdigital transducer is arranged at the center and symmetrically arranged at both ends of the surface wave propagation path in the surface wave propagation direction.
Using a plurality of comb-shaped electrodes electrically connected in parallel,
The center interdigital transducer and each pair of interdigital transducers electrically connected in parallel are electrically connected in series to form a one-terminal pair surface acoustic wave resonator on a piezoelectric substrate, and the surface acoustic wave resonator A surface acoustic wave resonator characterized by being weighted so that the excitation intensity of the surface acoustic wave gradually or gradually decreases from the center of the surface toward the outside in the propagation direction of the surface acoustic wave propagation path. 2. The surface wave resonator according to claim 1, wherein the surface wave excitation intensity is weighted by changing the cross width of the interdigital transducer. 3. The surface acoustic wave resonator according to claim 1, wherein the surface acoustic wave excitation intensity is weighted by thinning out the electrode fingers of the interdigital transducer or by using a dummy electrode. Resonator. 4. The surface wave resonator according to claim 1, 2 or 3, wherein the interdigital electrodes connected in series have substantially the same capacitance for each stage. Wave filter. 5. A surface acoustic wave filter comprising a combination of a surface acoustic wave resonator, an inductance and a capacitance, wherein the surface acoustic wave resonator according to any one of claims 1 to 4 is used. .. 6. A demultiplexer for mobile radio equipment, which uses the surface wave filter according to claim 5. 7. A mobile radio device using the surface acoustic wave filter according to claim 5. 8. A mobile radio device using the demultiplexer according to claim 6.