JPH11340779A - Surface acoustic wave filter, duplexer, and communication equipment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ladder type surface acoustic wave filter which has steepness improved nearby its passing band by decreasing an inductance value added to parallel arms of the surface acoustic wave filter. SOLUTION: The surface acoustic wave filter 10 is constituted of a package 11, input/output pads 13a, 13b formed on the package 11, earth pads 14a, 14b, 14c, 14d and a terminal electrode, a detour electrode connecting the input/output pads 13a, 13b and the earth pads 14a-14d to the terminal electrode, and a surface acoustic wave element 20 housed in the package 11 and constituted by connecting surface acoustic wave resonators 31 and 32 to series arms and connecting surface acoustic wave resonators 33, 34, and 35 to the parallel arms on a piezoelectric substrate 21. At this time, one end 45 of the surface acoustic wave resonator 35 connected to the parallel arms is connected to the two earth pads 14b and 14d by a wire 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ladder-type surface acoustic wave filter, a duplexer, and a communication device each having a surface arm connected to a series arm and a parallel arm.

[0002]

2. Description of the Related Art The configuration of a general ladder type surface acoustic wave filter is shown in FIGS. FIG. 11 is a schematic plan view of the surface acoustic wave filter, and FIG. 12 is a sectional view taken along line ZZ in FIG. Further, in FIG. 11, in order to better show the internal state, a diagram in which a lid portion is removed is used.

As shown in FIGS. 11 and 12, a ladder type surface acoustic wave filter 110 includes a package 111, a surface acoustic wave element 120 housed in the package 111, and a wire connecting the package 111 and the surface acoustic wave element 120. 112.

The package 111 is formed of alumina or the like, and the input / output pad 113 and the ground pad 114 are formed by printing and plating metal. Also,
On the bottom surface of the package 111, a terminal electrode 115 for surface mounting on a circuit board (not shown) is formed.
And the grounding terminal electrode 115 are connected by a routing electrode 116 formed on the package 111, respectively.

The surface acoustic wave element 120 housed in the package 111 is composed of a piezoelectric substrate 121 and surface acoustic wave resonators 131, 132, 133, 134 and 135 formed thereon. In this figure, a surface acoustic wave resonator 13
1 and 132 are arranged, and the surface acoustic wave resonators 133, 134 and 13 are
A ladder-type surface acoustic wave element 120 provided with 5 is used.

A surface acoustic wave resonator 13 connected to a parallel arm
One end of each of 3, 134 and 135 is connected to the ground pad 114, and one end of each of the surface acoustic wave resonators 131 and 132 connected to the series arm is connected to the input / output pad 113 by wire bonding.

Conventionally used in mobile communication equipment, etc.
For such a ladder-type surface acoustic wave filter, it has been required to further increase the passband width, increase the degree of suppression outside the passband, and realize low loss.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 5-183380, a method has been proposed in which an inductance is added between a surface acoustic wave resonator connected to a parallel arm and a ground pad. ing. FIG. 13 shows this circuit diagram. By doing so, the pass band width can be widened and the degree of suppression outside the pass band can be increased.

[0009] However, the problem that the steepness near the pass band is deteriorated when the inductance is added,
Newly arise. This is further exacerbated by the added inductance.

On the other hand, as disclosed in JP-A-6-164309, a method of adding a plurality of inductances in parallel between a surface acoustic wave resonator connected to a parallel arm and a ground pad. Has been proposed. Specifically, the surface acoustic wave resonator connected to the parallel arm and the ground pad are connected by a plurality of wires. This schematic plan view is shown in FIG. At a high frequency such as 800 MHz to 900 MHZ or 1.5 GHz used in mobile communication devices, an elongated wire, a high-impedance strip line, or the like functions as an inductance.

Here, for example, assuming that two wires of the same shape are connected in parallel, and the inductance value per one wire is L _W , the inductance value L between the surface acoustic wave resonator and the ground pad is represented by L _{W. 2,} consisting of _{1 / L 2 = 1 / L} w + 1 / L w and L ₂ = L _w / _2. Thus, between the connected surface acoustic wave resonators and ground pads parallel arm, the inductance value L ₂ when connecting the wire two, the inductance value L ₁ (= L when connecting with one wire _w ). Note that, here, for simplicity of description, wires having the same shape and the same inductance value have been described. However, even if wires having different inductance values are connected in parallel, the overall inductance value is reduced. I do. By doing so, the steepness near the pass band is improved.

[0012]

As described above, at high frequencies, elongated lines also function as inductances. Therefore, the routing electrode formed on the surface acoustic wave filter package that connects the ground pad and the terminal electrode also functions as an inductance. Therefore, the inductance value added to the surface acoustic wave resonator connected to the parallel arm is the difference between the inductance value between the surface acoustic wave resonator and the ground pad and the inductance value between the ground pad and the terminal electrode. This is the total value.

On the other hand, in the conventional surface acoustic wave filter, a plurality of wires are connected in parallel between the surface acoustic wave resonator and the ground pad, thereby reducing the inductance value.

Here, it is assumed that two wires of the same shape are connected in parallel between, for example, a surface acoustic wave resonator connected to a parallel arm and an earth pad. This circuit diagram is shown in FIG. By doing so, the inductance value L between the surface acoustic wave resonator having two wires connected thereto and the ground pad is determined.
₂ is L ₂ = L _w / 2 as described above. Further, when the inductance value between the grounding pad and the terminal electrode and L _P, inductance value L is added to the surface acoustic wave resonator, since L = L ₂ + L _P, is _{L = L w / 2 + L} P .
Therefore, no matter how many wires are connected in parallel between the surface acoustic wave resonator and the earth pad,
L cannot be less than L _P.

As described above, the conventional surface acoustic wave filter has a problem that since L is not smaller than L _P , there is a limit in improving the performance near the pass band.

Further, connecting a large number of wires between one surface acoustic wave resonator connected to the parallel arm and the ground pad is time-consuming and inefficient, and furthermore, there is a possibility that the wires may come into contact with each other. There was such a problem.

The surface acoustic wave filter of the present invention has been made in view of the above-mentioned problems, and solves these problems to efficiently reduce the inductance added to the surface acoustic wave resonator connected to the parallel arm. To the vicinity of the passband,
In particular, it is an object of the present invention to provide a surface acoustic wave filter capable of improving the steepness in a lower pass band.

[0018]

In order to achieve the above object, a surface acoustic wave filter according to the present invention comprises a package, an input / output pad, a ground pad, and a terminal electrode formed on the package; At least one surface acoustic wave resonator is connected to a serial arm on a piezoelectric substrate, and at least one surface acoustic wave resonator is connected to a parallel arm on a routing electrode connecting the pad and the terminal electrode. In a surface acoustic wave filter comprising a surface acoustic wave element and the surface acoustic wave element is housed in the package, one end of at least one surface acoustic wave resonator connected to the parallel arm has at least two or more Connected to ground pad.

According to the second aspect of the present invention, one ends of all surface acoustic wave resonators connected to the parallel arm are
It is connected to at least two or more ground electrodes.

Further, the duplexer of the present invention includes at least two filters, input / output connection means connected to each of the filters, and antenna connection means commonly connected to the filters. Claims: 1. A duplexer, wherein at least one of the filters is
3. The surface acoustic wave filter according to 1 or 2.

Further, a communication apparatus according to the present invention is a duplexer according to claim 3, a transmission circuit connected to at least one input / output connection means of the duplexer, and a transmission circuit connected to the transmission circuit. A receiving circuit connected to at least one input / output connection means different from the input / output connection means, and an antenna connected to the antenna connection means of the duplexer.

Thus, the inductance added to the surface acoustic wave resonator connected to the parallel arm can be reduced efficiently.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface acoustic wave filter according to an embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic plan view of the surface acoustic wave filter, and FIG.
FIG. 3 is a sectional view taken along line XX of FIG. 1, and FIG. 3 is a circuit diagram. Further, in FIG. 1, in order to better show the internal state, a diagram in which a lid portion is removed is used.

As shown in FIGS. 1 and 2, a surface acoustic wave filter 10 of the present invention comprises a package 11, a surface acoustic wave element 20 housed in the package 11, and a wire connecting the package 11 and the surface acoustic wave element 20. It consists of 12 and.

The package 11 is made of alumina or the like, and has input / output pads 13a, 13b, ground pads 14a, 14b, 14
c and 14d are formed by printing and plating metal. Further, on the bottom surface of the package 11, a terminal electrode 15 for surface mounting on a circuit board is formed,
Input / output pads 13a, 13b, terminal electrode 15, ground pad 14
The terminals a, 14b, 14c, and 14d and the terminal electrode 15 for grounding are connected to each other by a routing electrode 16 formed on the package 11.

The surface acoustic wave device 20 housed in the package 11 is composed of a piezoelectric substrate 21 and surface acoustic wave resonators 31, 32, 33, 34, 35 formed thereon.
As the piezoelectric substrate 21, a piezoelectric substrate of quartz, LiTaO ₃ , LiNbO ₃ or the like, or a substrate in which a ZnO film is formed on an insulating substrate of sapphire or the like is used. In this embodiment,
36 ° Ycut X direction propagation LiTaO with relatively high electromechanical coupling coefficient
_The passband is broadened using ₃ . The surface acoustic wave resonators 31, 32, 33, 34, 35 are composed of comb electrodes facing each other and reflectors on both outer sides in the direction of propagation of the surface waves, and are formed by vapor deposition of Al, photolithography, or the like. The reflector is for effectively confining energy, and may not be present in some cases. In this figure, a ladder-type surface acoustic wave element 20 having surface acoustic wave resonators 31 and 32 arranged in series arms and surface acoustic wave resonators 33, 34 and 35 arranged in parallel arms is used.

One end 41 of the surface acoustic wave resonator 31 disposed on the series arm is connected to the input / output pad 13b by the wire 12,
One end 42 of the surface acoustic wave resonator 32 arranged on the serial arm is connected to the input / output pad 13a by the wire 12. One end 43 of the surface acoustic wave resonator 33 disposed on the parallel arm and the ground pad 14c are connected by the wire 12, and one end 44 of the surface acoustic wave resonator 34 disposed on the parallel arm and the ground pad 14c.
a is connected by a wire 12, and one end 45 of a surface acoustic wave resonator 35 arranged in a parallel arm and a ground pad 14b are connected to the wire 1
Connected by two. Further, one end 45 of the surface acoustic wave resonator 35 connected to the parallel arm and the ground pad 14d
Connected by two.

The inductance values between the surface acoustic wave resonators 33, 34, 35 connected to the respective parallel arms and the ground pads 14a, 14b, 14c, 14d are assumed to be the same value, and the inductance value is assumed to be the same. Let _Lw . Further, assume that the inductance value also equal in lead-out electrode 16 between each of the ground pads 14a, 14b, 14c, 14d and the terminal electrodes 15 and the inductance value L _P.

FIG. 3 shows a circuit diagram when the connection is made by the wires 12 as described above. By connecting one end 45 of the surface acoustic wave resonator 35 to the two different ground pads 14b and 14d with the wire 12, the inductance is also parallel in the routing electrode 16 as shown in FIG. Accordingly, inductance value L between the surface acoustic wave resonator 35 and the terminal electrodes 15, than 1 / L = 1 / (L w + L P) + 1 / (L w + L P), L = (L w + L P ) / 2. This L is defined as the inductance value L = L between the surface acoustic wave resonator and the terminal electrode when one surface acoustic wave resonator and one ground pad are connected by two wires as in the prior art. compared to _w / 2 + L _P, while using the wire of the same number, obviously inductance value is L <L.

The surface acoustic wave filter 10 thus formed
FIG. 4 shows a characteristic diagram of the above. Note that the solid line is a characteristic diagram of the surface acoustic wave filter 10 of the present embodiment, and the broken line is a characteristic diagram of the conventional surface acoustic wave filter. As shown in FIG. 4, in the surface acoustic wave filter 10 of the present embodiment, the steepness in the vicinity of the pass band, particularly in the low band side is improved.

Next, a surface acoustic wave filter according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a schematic plan view of the surface acoustic wave filter,
6 is a sectional view taken along line YY of FIG. 5, and FIG. 7 is a circuit diagram.
Further, in FIG. 5, in order to better show the internal state, a diagram in which a lid portion is removed is used. Further, the same parts as those in the previous embodiment are denoted by the same reference numerals, and the detailed description is omitted.

As shown in FIG. 5, in the surface acoustic wave filter 10a of the present embodiment, one end 41 of a surface acoustic wave resonator 31 disposed in a series arm is connected to an input / output pad 13b by a wire 12. One end 42 of the surface acoustic wave resonator 32 arranged on the serial arm is connected to the input / output pad 13a by the wire 12. Further, one end 43 of the surface acoustic wave resonator 33 arranged on the parallel arm and the ground pad 14c are connected by the wire 12,
One end 44 of the surface acoustic wave resonator 34 disposed on the parallel arm and the ground pad 14a are connected by the wire 12, and one end 45 of the surface acoustic wave resonator 35 disposed on the parallel arm and the ground pad 14b are connected to the wire 12 Connected by Further, one end 43 of the surface acoustic wave resonator 33 disposed on the parallel arm and the ground pad 14a
Are connected by a wire 12, and one end 44 of a surface acoustic wave resonator 34 arranged in a parallel arm and a ground pad 14d are connected to the wire 12
Surface acoustic wave resonator 35 connected by
End 45 and ground pad 14d are connected by wire 12.

It is assumed that the inductance values between the surface acoustic wave resonators 33, 34, 35 connected to all the parallel arms and the ground pads 14a, 14b, 14c, 14d are the same, and the value is L.
_W , all ground pads 14a, 14b, 14c, 14d and terminal electrode 1
Inductance value between 5 is assumed to be identical to the value and L _P. FIG. 7 shows a circuit diagram when such connection is made. Each of the surface acoustic wave resonators 33, 34, 35 connected to the parallel arms is connected to two different ground pads. Thus, the inductance value between the surface acoustic wave resonator 33 and the terminal _{electrodes, 1 / (L w + L} P) +
Than _{1 / (L w + L P} ), (L w + L P) / 2, the surface acoustic wave resonators 34
The inductance value between the terminal electrodes _{and, (L w + L P)} /
2, the inductance value between the surface acoustic wave resonator 35 and the terminal electrodes are also _{(L w + L P) /} 2. In this way, the inductance value between the surface acoustic wave resonator connected to the parallel arm and the terminal electrode can be reduced more efficiently than the conventional surface acoustic wave filter.

The surface acoustic wave filter 10 thus formed
FIG. 8 shows a characteristic diagram of a. Note that the solid line is a characteristic diagram of the surface acoustic wave filter 10a of the present embodiment, and the broken line is a characteristic diagram of the surface acoustic wave filter of the first embodiment. As shown in FIG. 8, near the pass band in the surface acoustic wave filter 10 of the present embodiment,
Particularly, the sharpness on the low frequency side is further improved.

In the above two embodiments, for simplicity of explanation, the inductance values between the respective surface acoustic wave resonators and the ground pad are all the same, and the respective ground pads, terminal electrodes and Are all the same. However, even if the inductance value between each surface acoustic wave resonator and the ground pad and the inductance value between each ground pad and the terminal electrode are different from each other, by connecting them in parallel, The inductance value between the wave resonator and the terminal electrode is lower than before.

As described in Embodiments 1 and 2, by connecting the surface acoustic wave resonator connected to the parallel arm to two or more different ground pads, the inductance of the routing electrode portion is also parallel, and the efficiency is improved. Thus, the inductance value between the surface acoustic wave resonator and the terminal electrode can be reduced.

Further, the duplexer of the present invention will be described with reference to FIG. FIG. 9 is a schematic circuit diagram of the duplexer of the present invention. As shown in FIG. 9, the duplexer 40 of the present embodiment includes a first filter unit 41 formed of a surface acoustic wave filter and a second filter unit 42 formed of another surface acoustic wave filter. The surface acoustic wave filter constituting the first filter unit 41 is of a ladder type and serves as a transmission band-pass filter. The surface acoustic wave filter constituting the second filter unit has a resonance frequency different from that of the first filter unit 41, and serves as a bandpass filter for reception. The input 41a of the first filter unit 41 is connected to an external transmission circuit, and the output 42b of the second filter unit 42 is connected to an external reception circuit. Further, an output 41b of the first filter unit 41 and an input 42a of the second filter unit 42 are connected to an antenna connection terminal 43.
And is connected to an external antenna.

The duplexer 40 having such a configuration functions as a band-pass duplexer that passes a predetermined frequency in the first filter unit 41 and passes a frequency different from the previous frequency in the second filter unit 42.

In the duplexer of this embodiment, one end of the surface acoustic wave resonator connected to the parallel arm is connected to two ground pads. Therefore, the inductance between the electrode connected to the outside and the ground pad is also parallel, and the inductance value between the surface acoustic wave resonator and the ground can be reduced. Generally, the pass band on the transmitting side and the pass band on the receiving side are often close to each other. On the other hand, it is necessary to increase the isolation between the transmitting side and the receiving side. That is, it is necessary to sufficiently attenuate the pass band on the receiving side for the transmitting filter and the transmitting band for the receiving filter. Here, for example, when the pass band of the transmitting filter is on the low band side and the pass band of the receiving filter is on the high band side, by using the present invention, particularly, the steepness near the low band side of the pass band of the receiving filter is obtained. This makes it possible to provide a duplexer having an excellent attenuation in the band of the transmission-side filter. Note that the duplexer of the present invention can be configured such that two filters are formed on the same substrate.
It may be formed on another substrate.

Further, a communication device according to an embodiment of the present invention will be described with reference to FIG. FIG. 10 is a schematic diagram of the communication device of the present embodiment. As shown in FIG. 10, the communication device 50 of the present embodiment includes a duplexer 40, a transmission circuit 51, a reception circuit 52, and an antenna 53. Here, the duplexer 40 is the one shown in the previous embodiment, the input side of the first filter unit 41 in FIG. 9 is connected to the transmission circuit 51, and the output side of the second filter unit 42 is the reception circuit 52. It is connected to the. The antenna connection terminal is connected to the antenna 53.

In the communication device of this embodiment, one end of the surface acoustic wave resonator connected to the parallel arm is connected to two ground pads. Therefore, the inductance between the externally connected electrode and the ground pad is also in parallel,
The inductance value between the surface acoustic wave resonator and the ground can be reduced. Therefore, it is possible to provide a duplexer that is characteristically preferable.

[0042]

As described above, according to the present invention, in a ladder type surface acoustic wave filter, one end of at least one surface acoustic wave resonator connected to a parallel arm is connected to at least two or more ground pads. Connected. Thereby, the inductance between the ground pad and the terminal electrode is also parallel, and the inductance value between the surface acoustic wave resonator and the terminal electrode can be reduced. Therefore, the steepness in the vicinity of the pass band of the surface acoustic wave filter, particularly on the low frequency side, is increased, and a surface acoustic wave filter, a duplexer, and a communication device that are favorable in characteristics can be obtained.

Further, the inductance can be efficiently reduced with a smaller number of wires as compared with the conventional case where the surface acoustic wave resonator connected to the parallel arm and the ground pad are connected by a large number of wires. Can be. In addition, it is possible to reduce a possibility that the wires come into contact with each other.

Further, one ends of all the surface acoustic wave resonators connected to the parallel arms were connected to at least two or more earth pads. Thereby, the inductance value between the surface acoustic wave resonator and the terminal electrode can be more efficiently reduced. Therefore, the steepness in the vicinity of the pass band of the surface acoustic wave filter, especially in the low band side, is increased, and a surface acoustic wave filter, a duplexer, and a communication device that are favorable in characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a surface acoustic wave filter according to the present invention.

FIG. 2 is a sectional view taken along line XX of the surface acoustic wave filter of FIG.

FIG. 3 is a circuit diagram of a surface acoustic wave filter according to the present invention.

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

FIG. 5 is a schematic plan view of the surface acoustic wave filter of FIG.

FIG. 6 is a sectional view taken along line YY of a surface acoustic wave filter according to a second embodiment of the present invention.

FIG. 7 is a circuit diagram of a surface acoustic wave filter according to a second embodiment of the present invention.

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

FIG. 9 is a schematic circuit diagram of a duplexer according to the present invention.

FIG. 10 is a schematic diagram of a communication device of the present invention.

FIG. 11 is a schematic plan view of a conventional general surface acoustic wave filter.

FIG. 12 is a sectional view taken along the line ZZ of the surface acoustic wave filter of FIG. 9;

FIG. 13 is a circuit diagram of a surface acoustic wave filter in which an inductance is added to a surface acoustic wave resonator of a parallel arm.

FIG. 14 is a schematic plan view of a surface acoustic wave filter in which a surface acoustic wave resonator and an earth pad are connected by two wires.

FIG. 15 is a circuit diagram of a surface acoustic wave filter in which a surface acoustic wave resonator and an earth pad are connected by two wires.

[Explanation of symbols]

 10 Surface acoustic wave filter 11 Package 13a, 13b Input / output pad 14a, 14b, 14c, 14d Ground pad 15 Terminal electrode 16 Leading electrode 20 Surface acoustic wave element 21 Piezoelectric substrate 31, 32, 33, 34, 35 Surface acoustic wave resonance Child 40 Duplexer 41 First filter part 42 Second filter part 43 Terminal for antenna connection 50 Communication equipment 51 Transmission circuit 52 Reception circuit 53 Antenna

Claims (4)

[Claims] A package, an input / output pad, a ground pad, and a terminal electrode formed on the package; a routing electrode for connecting the input / output pad, the ground pad to the terminal electrode; A surface acoustic wave element in which at least one surface acoustic wave resonator is connected to the serial arm and at least one surface acoustic wave resonator is connected to the parallel arm; and the surface acoustic wave element is housed in the package. A surface acoustic wave filter according to claim 1, wherein one end of at least one surface acoustic wave resonator connected to the parallel arm is connected to at least two or more ground pads. 2. The surface acoustic wave filter according to claim 1, wherein one ends of all surface acoustic wave resonators connected to the parallel arm are connected to at least two or more ground electrodes. 3. A duplexer comprising: at least two filters; input / output connection means connected to each of said filters; and antenna connection means commonly connected to said filters. 3. A duplexer, wherein at least one of the filters is the surface acoustic wave filter according to claim 1. 4. The duplexer according to claim 3, a transmission circuit connected to at least one input / output connection means of the duplexer, and different from the input / output connection means connected to the transmission circuit. A communication device, comprising: a receiving circuit connected to at least one input / output connection means; and an antenna connected to an antenna connection means of the duplexer.