JPH09252232A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deterioration of insertion loss via a simple circuit constitution by inserting a single terminal paired SAW(surface acoustic wave) resonator and a capacitor in series between the connection point of two parallel SAW filters and a 1st SAW filter. SOLUTION: A capacitor 25 and a single terminal paired SAW resonator 26 are connected between a 1st SAW filter 22 and a connection point 24. The capacitor 25 has its impedance larger than 1/4 terminal impedance of an SAW device 21, and the resonator 26 has its anti-resonance frequency that is higher than the pass band of the filter 22. In such a constitution, it is possible to suppress the increase of insertion loss of the filter 22 and also the deterioration of VSWR in a pass band when the impedance must be increased in the pass band of a 2nd SAW filter 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device formed by combining a plurality of SAW filters, for example, a surface acoustic wave device used in a mobile communication device having two or more frequency bands.

[0002]

2. Description of the Related Art In recent years, mobile communication devices have become more sophisticated, and, for example, multi-band mobile phones having two or more communication systems have been studied. In order to realize such a mobile phone, a wide band pass filter capable of covering two or more bands is required. However, it has been difficult to realize a low-loss, wide-band filter that can cover two or more bands with a single element.

Therefore, it has been attempted to construct a wideband bandpass filter by combining a plurality of bandpass filters into one component. For example,
Japanese Patent Laid-Open No. 4-16014 discloses a broadband surface acoustic wave device formed by combining a plurality of band pass filters as described above. The structure of the surface acoustic wave device disclosed in this prior art will be described with reference to FIG.

The surface acoustic wave device 1 shown in FIG.
The AW filters 2 and 3 are connected in parallel on the output side. That is, SA is applied to the input terminals IN ₁ and IN ₂ , respectively.
The W filters 2 and 3 are connected, and the outputs of the SAW filters 2 and 3 are connected in parallel at the connection point 4.
The pass band of the SAW filter 2 is set higher than that of the SAW filter 3.

A capacitor 5 as a reactance element is connected between the SAW filter 2 and the connection point 4. Further, an inductance element 6 is connected as a second reactance element between the connection point 4 and the ground potential.

In mobile phones, transmission and reception are performed at different frequencies. In the surface acoustic wave device 1, the transmission-side bandpass filter and the reception-side bandpass filter in the mobile phone can be configured by a single component by combining the SAW filters 2 and 3.

In the surface acoustic wave device 1, one SA
The insertion loss is reduced by inserting a reactance element such as a capacitor 5 between the W filter 2 and the connection point 4.

[0008]

The surface acoustic wave device 1 uses the SAW filters 2 and 3 having different pass band frequency characteristics as described above. In this case, the SAW filters 2 and 3 are: It may not always be possible to prepare the one having the optimum impedance characteristic.

On the other hand, when the impedance in the pass band of the SAW filter 3 of the SAW filter 2 on the side to which the capacitor 5 as the reactance element is connected is low,
In order to reduce the insertion loss, it is necessary to increase the impedance of the capacitor 5. However, when the impedance of the reactance element is increased, the impedance of the pass band of the SAW filter 2 on the side where the reactance element is inserted also becomes high. As a result, the deterioration of VSWR in the pass band causes the SAW filter 2 side There was a problem that the insertion loss deteriorated.

Therefore, in the above-mentioned prior art, in order to compensate for the deterioration of VSWR in the pass band, the inductance element 6 is connected as the second reactance element between the connection point 4 and the ground potential. However, in this case, conversely, due to the influence of the inductance element 6, S
The VSWR in the pass band of the AW filter 3 is deteriorated. Therefore, in the configuration in which the inductance element 6 is connected, it is necessary to further connect the impedance matching reactance element in the SAW filter 3 as in the SAW filter 2 side. As a result, there is a drawback that the number of impedance matching elements increases and the circuit configuration becomes complicated.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and is to be realized with a relatively small number of parts and a relatively simple circuit configuration, with few restrictions on the impedance characteristics of the SAW filter used. VSW in the pass band
An object of the present invention is to provide a surface acoustic wave device having a plurality of pass band characteristics capable of reducing R.

[0012]

According to a broad aspect of the present invention, there is provided a surface acoustic wave device having a plurality of SAW filters connected to each other, which has a relatively high pass band in order to achieve the above object. A first SAW filter in the frequency domain and a second SAW in the frequency domain having a relatively low pass band and connected in parallel to the first SAW filter at a connection point on the input end or output end side. A filter, a capacitor element that is connected between the first SAW filter and the connection point, and has an impedance that is ¼ or more of the termination impedance of the surface acoustic wave device; the capacitor element and the first SAW. It is connected between the filter and the anti-resonance frequency of the first SA
Provided is a surface acoustic wave device including a one-terminal pair SAW resonator configured to be on a higher frequency side than a pass band of a W filter.

Further, according to a specific aspect of the present invention, the first SAW filter includes a piezoelectric substrate and an odd number of interdigital transducers (hereinafter abbreviated as IDT) formed on the piezoelectric substrate. A multi-electrode vertical coupling SAW resonator filter having a pair of reflectors formed on both sides of the region where the odd number of IDTs are formed, and adjacent to the pair of reflectors. A pair of I
There is provided a surface acoustic wave device in which the one-terminal pair SAW resonator is connected in series to a plurality of IDTs including a DT.

According to still another specific aspect of the present invention, each of the first and second SAW filters is formed by using a piezoelectric substrate, and the capacitor element has first and second capacitor elements. The piezoelectric substrate of the second SAW filter is formed on one of the piezoelectric substrates.

In the present invention, as the piezoelectric substrate, a piezoelectric single crystal, a piezoelectric ceramic, an insulating or piezoelectric substrate on which a piezoelectric thin film is formed, or the like is appropriately used.

According to a more limited aspect of the present invention, the first and second SAW filters are formed by using the same piezoelectric substrate. Further, according to another specific aspect of the present invention, the piezoelectric substrate is 36 ° Y-X L.
When an iTaO ₃ substrate is used and the center frequency of the pass band of the first SAW filter is f ₀₁ and the center frequency of the second SAW filter is f ₀₂ ,

[0017]

[Equation 2]

There is provided a surface acoustic wave device configured to satisfy the relationship of

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Prior to explaining the structure of a surface acoustic wave device of the present invention, a surface acoustic wave device which the present applicant has previously filed and which is related to the present invention but is not yet known is illustrated. 2 will be described.

The surface acoustic wave device 11 shown in FIG. 2 has a first band pass filter 12 having a relatively high pass band frequency.
And a second band-pass filter 13 having a relatively low pass band frequency are connected in parallel on the output side. That is, the input terminals IN ₁ and IN ₂ are respectively connected to the first and first terminals.
The second bandpass filters 12 and 13 are connected, and the outputs of the bandpass filters 12 and 13 are the connection points 14
Are connected in parallel at.

Further, between the output end of the second bandpass filter 13 having a relatively low passband frequency and the connection point 14, the antiresonance frequency is within the passband of the first bandpass filter 12, or At least one one-terminal pair SAW resonator 15 located between the pass bands of the first and second band pass filters 12 and 13 is connected in series.
Further, an impedance matching element formed of the transmission line 16 is connected between the first bandpass filter 12 and the connection point 14.

The first and second bandpass filters 1
2 and 13 are at least the second bandpass filter 13
Is composed of a SAW filter. In the surface acoustic wave device 11, by connecting the one-terminal pair SAW resonator 15 to the second bandpass filter 13 having a relatively low passband frequency, the attenuation amount in the high frequency range of the bandpass filter 13 is increased. At the same time, the impedance matching external circuit on the side of the band pass filter 13 is simplified.

However, since the transmission line 16 is connected to the first bandpass filter 12 having a relatively high pass band frequency, when the transmission line having a desired line length is formed, the bandpass filter 12 and thus the elastic surface. There is a problem that the overall size of the wave device 11 becomes large.

In order to reduce the size and increase the functionality,
When the surface acoustic wave device 11 is built in the surface acoustic wave device package, it is necessary to make the width of the transmission line 16 extremely narrow in order to obtain a desired characteristic impedance. As a result, the insertion loss may deteriorate due to the resistance loss of the transmission line 16. Further, when the device is built in the package as described above, the area and height of the package become large, and in addition, there is a risk of increasing the cost.

When the difference between the pass band frequencies of the band pass filters 12 and 13 is relatively small, the other side of the first band pass filter 12 having a relatively high frequency, that is, the second band pass filter 13 has a relatively high frequency. The impedance in the pass band becomes low, and even if a one-terminal pair SAW resonator is used instead of the transmission line 16, the impedance is not sufficiently high, and deterioration of the insertion loss of the other side, that is, the SAW filter 13 is suppressed. There was also a problem that I could not do it.

That is, the inventors of the present invention have proposed the one-terminal pair SA.
The surface acoustic wave device 11 using the W resonator 15 has further problems in view of the above problems, and as a result, further investigation has led to the creation of the surface acoustic wave device according to the present invention.

Next, the structure of the surface acoustic wave device of the present invention will be described with reference to the drawings. FIG. 3 is a circuit diagram for explaining one embodiment of the surface acoustic wave device of the present invention.

The surface acoustic wave device 21 includes a first SAW filter 22 and a second SAW filter 23 having different pass bands.
It has a configuration in which and are connected in parallel on the output side. That is, the first SAW filter 22 having a relatively high pass band in the high frequency range is connected to the input end IN ₁ , and the input end IN ₁ is connected to the first SAW filter 22.
_{A second} SA whose pass band is in the low frequency region relative to 2.
The W filter 23 is connected.

The pass band of the first SAW filter 22 is
860-885 MHz, and the pass band of the second SAW filter 23 is 810-826 MHz. First and second S
The outputs of the AW filters 22 and 23 are connected at a connection point 24.

Further, a capacitor 25 and a one-terminal pair SAW are provided between the first SAW filter 22 and the connection point 24.
The resonator 26 is connected. The capacitor 25 is configured to have an impedance of ¼ or more of the termination impedance of the surface acoustic wave device 21. Also,
The one-terminal pair SAW resonator 26 is connected between the capacitor 25 and the first SAW filter 22, and its anti-resonance frequency is higher than the pass band of the first SAW filter 22. Is configured.

In this embodiment, the inductance element 27 as a reactance element is connected between the connection point 24 and the ground potential. This inductance element is connected outside the package. That is, the portion surrounded by the broken line indicated by reference numeral 28 is built in one package.

Since the surface acoustic wave filter device 21 is constructed as described above, the first SAW filter 22
On the side, when it is necessary to increase the impedance in the pass band of the second SAW filter 23, not only the capacitor 25 but also the one-terminal pair SAW resonator 26 is connected between the capacitor 25 and the first SAW filter 22. Therefore, it is possible to suppress an increase in insertion loss on the first SAW filter 22 side and a deterioration in VSWR in the pass band. Moreover, the second SAW filter 23
It is also possible to suppress the deterioration of the insertion loss.

In addition, it is possible to suppress an increase in insertion loss of the first SAW filter 22 and increase the amount of attenuation on the higher frequency side than the pass band of the first SAW filter 22.

The function and effect of the surface acoustic wave filter device 21 will be described based on a concrete experimental example. First and second S
As the AW filters 22 and 23, those having the characteristics shown in FIGS. 4 to 7 were used.

In FIG. 4, the center frequency of the pass band is 872.
It is a figure which shows the attenuation amount frequency characteristic of the 1st SAW filter 22 which is 5 MHz. The characteristic indicated by B in FIG. 4 is
The attenuation amount on the vertical axis is an enlargement of the characteristic shown by the solid line A according to the enlargement scale shown on the right side of the vertical axis.

5A and 5B are impedance Smith charts of the input terminal and the output terminal of the first SAW filter 22, respectively. FIG.
Shows the attenuation frequency characteristic of the second SAW filter 23 whose pass band has a center frequency of 818 MHz.
The characteristics indicated by are those obtained by enlarging the characteristics indicated by the solid line C according to the enlargement scale shown on the right side of the vertical axis. 7A and 7C are diagrams showing impedance Smith charts of the input side and output side terminals of the second SAW filter 23.

FIG. 8A shows a capacitor 2 of 3.5 pF.
5 is an impedance Smith chart seen from the output side when 5 is connected in series to the first SAW filter 22. As is clear from a comparison between FIG. 5B and FIG. 8A, in FIG. 8A, the impedance at 818 MHz is increased due to the connection of the capacitor. At the same time, the impedance in the vicinity of the pass band is largely deviated from 50Ω pure resistance to capacitive.

FIG. 9 shows attenuation-frequency characteristics inside and outside the pass band when the one-terminal pair SAW resonator 26 is connected in series on the output side of the first SAW filter 22, and FIG.
(A) and (b) are impedance Smith charts on the input side and the output side in that case. Note that, in FIG. 9, the curve indicated by the solid line F is the characteristic indicated by the solid line E enlarged according to the enlargement scale shown on the right side of the vertical axis.
In this case, as the one-terminal pair SAW resonator, the IDT having the number of electrode finger pairs = 130 pairs, the electrode finger crossing width = 60 μm and the electrode finger pitch = 2.2 μm is 36 ° Y-X LiTaO.
_The one formed on the piezoelectric substrate made of ₃ was used.

Comparing FIG. 5 (b) and FIG. 10 (b), it can be seen that the impedance at 818 MHz is increased by the one-terminal pair SAW resonator 26 in FIG. 10 (b). Further, comparing FIG. 10 (a) with FIG. 5 (a), in FIG. 10 (a), deterioration of insertion loss in the pass band of the first SAW filter 22 is suppressed, and the frequency is higher than the pass band. It can be seen that the amount of attenuation on the side is increased.

FIG. 8B shows an impedance Smith chart when the first and second SAW filters 22 and 23 are viewed from the parallel connection terminal side of the surface acoustic wave device 21 of this embodiment, that is, the connection point 24. . 8 (b), and FIG.
Compared to (a), the characteristics shown in FIG.
It can be seen that the equivalent impedance is obtained with a capacitor having a capacitance of 8 pF at 8 MHz. In this case, in the vicinity of the pass band, the deviation of the impedance from the 50Ω pure resistance to the capacitance is suppressed to be small.

For comparison, the surface acoustic wave device 1 shown in FIG. 1 was constructed using the same first and second SAW filters as those described above. That is, in the surface acoustic wave device 1,
The SAW filters 2 and 3 are used as the first and second SAWs.
The same as filters 22 and 23 are used, and capacitor 5
, The impedance at 818MHz is 3.5
A capacitor of pF was used, and an impedance matching inductance element 6 of 7.5 nH was used.
The first S of the surface acoustic wave device 1 configured as described above.
FIG. 11 shows the attenuation-frequency characteristics on the AW filter 2 side.
In addition, in FIG. 11, a solid line H is a characteristic obtained by enlarging the characteristic shown by the solid line G on the scale shown on the right side of the vertical axis. A broken line I indicates VSWR-frequency characteristic.

The first surface acoustic wave device 1
12A and 12B are impedance Smith charts of the input side and the output side of the SAW filter 2 of FIG. The input side of the second SAW filter 3 is terminated with 50Ω.

On the other hand, FIG. 13 shows the attenuation frequency characteristic on the first SAW filter 22 side when the surface acoustic wave filter device 21 according to the present embodiment is configured as shown in FIG. It is a figure. In FIG. 13, a solid line K is a characteristic obtained by enlarging the characteristic shown by the solid line J on the scale shown on the right side of the vertical axis, and a broken line L is a diagram showing VSWR-frequency characteristic. 14 (a) and (b)
FIG. 6 is a diagram showing an impedance Smith chart on the input side and the side of the parallel connection point 24 on the first SAW filter 22 side.

In this embodiment, the impedance matching inductance element 27 of 7.5 nH is inserted between the parallel connection point 24 and the ground point. The input side of the second SAW filter 23 is terminated with 50Ω.

Comparing FIG. 11 with FIG. 13, it can be seen that the increase in loss due to the insertion of the capacitor is suppressed in FIG. For example, a pass band width with an attenuation amount of 3.1 dB, that is, a so-called 3.1 dB bandwidth is 32.
While it was 5 MHz, in FIG. 13, it is 33.3 MHz.
It was expanded. At the same time, as for VSRW, the maximum value at 860 to 885 MHz is 1.
While it was 75, it can be seen that it is as small as 1.3 in FIG. Furthermore, it can be seen that the amount of attenuation in the frequency region on the high frequency side of the pass band is large.

FIG. 15 shows the second S in the above embodiment.
It is a figure which shows the attenuation amount frequency characteristic in the AW filter 23. In FIG. 15, a solid line N is an enlargement of the characteristic indicated by the solid line M on the scale of the attenuation amount on the vertical axis on the right side of the vertical axis, and a broken line O indicates the VSWR-frequency characteristic. 16A and 16B are diagrams showing impedance Smith charts on the input side of the second SAW filter 23 and the parallel connection point 24 side. An impedance matching inductance element 27 of 7.5 nH is used between the parallel connection point 24 and the ground potential. The input side of the first SAW filter 22 is terminated with 50Ω. As is clear from the comparison of FIG. 15 with FIG. 6, it can be seen that the deterioration of the insertion loss on the second SAW filter 23 side can be suppressed.

Unlike the present invention, FIG. 17 shows the first SAW filter 22 and the second SAW filter 23.
A second SAW filter 2 having a configuration in which and are directly connected in parallel.
3 shows an attenuation frequency characteristic of No. 3. In FIG. 17, the solid line Q
Shows the characteristic shown by the solid line P in an enlarged scale of the attenuation amount on the vertical axis on the right side of the vertical axis, and the broken line R shows VS.
The WR-frequency characteristic is shown. 18A and 18B are diagrams showing impedance Smith charts on the input side and the output side in this case. As is clear from FIG. 17, in this case, it is found that the insertion loss increases.

FIG. 19 is a schematic plan view of a surface acoustic wave filter device according to a second embodiment of the present invention. FIG.
In, the multi-electrode type longitudinally coupled SAW resonator filter 32 is formed as the first SAW filter on the piezoelectric substrate 31 made of 36 ° Y-X LiTaO ₃ . That is, the SAW resonator filter 32 includes three IDTs 33-.
35. The IDTs 33 to 35 are alternately set to the input side IDT or the output side IDT along the surface wave propagation direction. Each of the IDTs 33, 34, 35 is composed of a pair of comb-teeth electrodes having electrode fingers which are inserted into each other.
Reflectors 36 and 37 are arranged outside the area where the IDTs 33 to 35 are provided in the surface wave propagation direction.

Out of the IDTs 33 to 35, the outer IDT 3
One of the comb-teeth electrodes 3 and 35 is grounded, and the other comb-teeth electrode is the output side terminal. Also, the center I
One of the comb-teeth electrodes of the DT 34 is grounded, and the other comb-teeth electrode thereof is connected to the input terminal IN ₁ .

FIG. 20 shows an example of the attenuation frequency characteristic of the SAW resonator filter 32. In FIG. 20, a solid line T is a characteristic obtained by enlarging the main part of the characteristic shown by the solid line S by the scale shown on the right side of the vertical axis for the amount of attenuation on the vertical axis.
21A and 21B are impedance Smith charts of the SAW resonator filter 32. FIG.
1 (a) shows the characteristics of the terminal connected to the input terminal IN ₁ of the central IDT 34, and FIG.
It is the characteristic in the output side terminal of 3,35.

On the output side of the SAW resonator filter 32,
A one-terminal pair SAW resonator 38 is provided. The one-terminal pair SAW resonator 38 is connected in series to the comb-teeth electrode that configures the output terminals of the IDTs 33 and 35 so that the anti-resonance frequency is on the higher frequency side than the pass band of the SAW resonator filter 32. Has been done.

The attenuation frequency characteristic of the configuration in which the one-terminal pair SAW resonator 38 is connected in series to the SAW resonator filter 32 is configured to match the characteristic shown in FIG. The chart is shown in FIG.
It is configured to match the characteristics shown in (a) and (b).

The one-terminal pair SAW resonator 38 and the connection point 3
The capacitor 40 is inserted in series between the capacitor 40 and the capacitor 9. S
The overall impedance Smith chart of the configuration in which the one-terminal pair SAW resonator 38 and the capacitor 40 are connected in series to the AW filter 32 is configured to match the characteristics shown in FIG. 8B. Here, the capacitance of the capacitor 40 is 8 pF. Therefore, as is clear from FIG. 8B, the impedance at 818 MHz is higher than that in the case of FIG. 5B.

Also in this embodiment, the inductance element 41 is connected between the connection point 39 and the ground potential. The inductance 41 has the same structure as the inductance 27 in the first embodiment. Also,
The second SAW filter 42 is connected to the input terminal IN ₂ , and the second SAW filter 42 is connected in parallel with the SAW filter 32 on the output side. That is,
The output side of the SAW filter 42 is connected to the connection point 39.

The SAW filter 42 has three IDTs 43.
To 45, and the reflectors 46 and 47 are arranged outside the region where the IDTs 43 to 45 are provided. Since the surface acoustic wave filter device 31 of the present embodiment is configured as described above, it exhibits the same function and effect as the surface acoustic wave filter device according to the first embodiment. In addition, SAW
The filter 32 is composed of a multi-electrode type longitudinally coupled SAW resonator filter and is connected in series to the one-terminal pair SAW resonator 38. The effect of this configuration will be described below.

In contrast to the above configuration, FIG. 20 shows one terminal pair S
It is the attenuation amount frequency characteristic on the SAW filter 32 side when the AW resonator 38 is connected in series to one comb tooth electrode of the center IDT 34 and then a capacitor having a capacitance of 15 pF is connected. 21A and 21B are impedance Smith charts on the input side and the output side in this case.
As is clear from FIG. 21 (b), the impedance at 818MHz is 818MHz shown in FIG. 8 (b).
It is almost the same as the impedance at.

Further, the SAW in the case where the second SAW filter 42 is connected in parallel to the structure having the characteristics shown in FIG.
FIG. 22 shows the attenuation frequency characteristics on the filter 32 side. In FIG. 22, a solid line V is a characteristic obtained by enlarging the characteristic shown by the solid line U on the scale shown on the right side of the vertical axis,
The broken line W indicates the in-passband VSWR.

The impedance Smith chart in this case is as shown in FIGS. 23 (a) and 23 (b). Here, an impedance matching inductance element 41 of 7.5 nH is used between the parallel connection point and the ground potential. The input side of the second SAW filter 42 is terminated with 50Ω.

A comparison between FIG. 22 and FIG. 13 shows that FIG.
In, the increase of insertion loss is suppressed, for example, 3.1.
The dB bandwidth is 30.5 MHz in FIG. 22, while it is expanded to 33.3 MHz in FIG. Similarly,
It can be seen that deterioration of VSWR is suppressed as much as possible.

This is 86 of the one-terminal pair SAW resonator 38.
Impedance at 0-880MHz and the first S
860 of the output side terminal of the IDT outside the AW filter 32
This is because the VSWR is reduced by combining with the impedance of MHz to 885 MHz.

In this embodiment, 36 ° Y-X L
Although a material made of iTaO ₃ is used, it is not limited to this, and other piezoelectric single crystals such as LiNbO ₃ or piezoelectric ceramics such as lead zirconate titanate-based piezoelectric ceramics, an insulating substrate or a piezoelectric material. A suitable piezoelectric substrate formed by forming a piezoelectric thin film on a flexible substrate can be used.

Next, another example of the specific structure of the surface acoustic wave device of the present invention will be described. FIG. 24 is a schematic plan view for explaining an example of a specific structure of the surface acoustic wave device of the present invention, in which the first SAW filter, the one-terminal pair SAW resonator and the capacitor are formed on the same substrate. The following is an example.

A multi-electrode type SAW resonator filter 53 is constructed as a first SAW filter on one piezoelectric substrate 52. That is, in the SAW resonator filter 53,
Three IDTs 54 to 56 are formed along the surface wave propagation direction. The IDTs 54 to 56 are alternately input side IDTs.
Alternatively, it is the output side IDT. The outer IDT 54,
One of the comb-teeth electrodes 56 is grounded, and the other comb-teeth electrode 56 is commonly connected by a connection point 57. Also,
One comb tooth electrode of the IDT 55 is grounded, and the other comb tooth electrode is electrically connected to the input lead electrode 58.

In FIG. 24, 59a, 59b, 59c
Are lead-out electrodes for connecting to the ground potential, respectively. Reflectors 60 and 61 are provided on both sides of the area where the IDTs 54 to 56 are provided in the surface wave propagation direction. Further, at the connection point 57, the one-terminal pair SAW resonator 62
Is connected. In addition, the one-terminal pair SAW resonator 62
Is connected to the capacitor 63.

The capacitor 63 is composed of a pair of comb-teeth electrodes in FIG. The other comb-shaped electrode of the capacitor 63 is connected to the connection electrode 64. The connection electrode 64 constitutes a connection point between the first SAW filter and the second SAW filter in the present invention. That is, although the second SAW filter is not shown in FIG. 24, the output side of the second SAW filter is connected to the connection electrode 64. In FIG. 24, the capacitor 6
Although 3 is formed on the same substrate as the SAW resonator filter 53 as the first SAW filter, the capacitor 63 may be formed on the piezoelectric substrate for forming the second SAW filter.

FIG. 25 is a sectional view for explaining a surface acoustic wave device incorporating the piezoelectric substrate 52 shown in FIG. In FIG. 25, the surface acoustic wave device of the present invention is built in the package.

That is, in the surface acoustic wave device 71, the upper opening of the package body 72 having the upper opening is sealed with the sealing material 73. The package body 72 can be made of an appropriate material such as insulating ceramics such as alumina or synthetic resin. In FIG. 25, the package main body 72 has a structure in which frame-shaped package materials 72b and 72c having an opening are laminated and attached on a base plate 72a. In the opening of the package body 72, the first SA is placed on the base plate 72a.
A piezoelectric substrate 52 provided with a W filter, a one-terminal pair SAW resonator and a capacitor on the same surface, and a piezoelectric substrate 75 forming a second SAW filter are fixed by an adhesive or the like.

The electrode terminals of the SAW filter on the piezoelectric substrates 52 and 75 are drawn out by wires 76 and 77 made of metal or the like, and are electrically connected to the extraction electrodes formed in the package body 72. The sealing material 73 can be made of ceramics, metal, or the like. In this case, the piezoelectric substrate 5 is formed on the lower surface of the sealing material 73.
You may form the extraction electrode from which the SAW filter comprised on 2,75 is drawn out suitably.

As shown in FIG. 25, the package body 72
A surface acoustic wave device of the present invention can be built in a package consisting of a sealing material 73 and a sealing material 73. Therefore, a bandpass filter having a plurality of pass bands capable of exhibiting the above-described effects as a single component is provided. Can be configured.

In the surface acoustic wave element 51 shown in FIG. 24,
Since the capacitor 63 is formed on the surface of the piezoelectric substrate 52, the capacitance value of the capacitor 63 can be easily changed. That is, the capacitance can be easily changed by changing the number of electrode fingers or the cross width of the comb-teeth electrode. Therefore, as shown in FIG. 25, when applied to a structure in which the piezoelectric substrate 52 on the surface of which the capacitor is formed is inserted into the package, it is necessary to change the package size in accordance with the change in the capacitance value of the capacitor. Absent. That is, since the package can be shared, the package cost can be reduced.

In addition, conventionally, when the first and second SAW filters having two pass bands are packaged as one surface acoustic wave device, all the input and output electrodes of the two SAW filters, that is, four electrodes. Had to be formed in the package. On the other hand, when the capacitor 63 shown in FIG. 24 is formed on the same piezoelectric substrate 52 as the first SAW filter, the number of output electrodes on one SAW filter side can be three. Therefore, the package can be further downsized. Or, conversely,
Since it is possible to increase the number of electrodes for grounding, it is possible to suppress the deterioration of the attenuation amount due to the direct wave of the SAW filter by strengthening the ground.

FIG. 26 is a schematic plan view showing an example in which the surface acoustic wave element 51 shown in FIG. 24 is developed so that the second SAW filter is also formed on the same piezoelectric substrate. 26, the surface acoustic wave element 5 shown in FIG.
The same parts as 1 are designated by the same reference numerals.

Referring to FIG. 26, the second SAW filter 81 is connected to the connection electrode 64 on the piezoelectric substrate 80. The second SAW filter 81 is the piezoelectric substrate 8
0, that is, the SAW as the first SAW filter
It is formed on the same substrate as the resonator filter 53.

The second SAW filter 81 has three IDs.
T82-84. The reflectors 85 and 86 are provided on both sides of the area where the IDTs 82 to 84 are provided in the surface wave propagation direction.
Are formed. One of the comb-teeth electrodes of the IDT 83 in the center of the second SAW filter 81 is the connection electrode 64 described above.
And the other comb-teeth electrode is connected to the ground lead electrode 87a. Also, the outer IDT8
One of the comb-shaped electrodes 2 and 84 is the extraction electrode 8 for input.
7b, and the other comb-shaped electrode is connected to the grounding lead-out electrodes 87c and 87d.

In the example shown in FIG. 26, all of the first and second SAW filters, capacitors and one-terminal pair SAW resonators are formed on the piezoelectric substrate 80. Therefore, as shown in the cross-sectional view of FIG. 27, the surface acoustic wave device can be easily incorporated in the package body 72, so that the work efficiency in packaging can be improved.

Further, since the two SAW filters are formed on one piezoelectric substrate 80, it is easy to keep the pass band intervals of the SAW filters substantially constant, and the two SAW filters are formed.
Compared to the case where the W filter is manufactured independently, it is possible to reduce the variation in characteristics. That is, when the frequency difference between them becomes small,
, The impedance in the pass band of the second SAW filter becomes low,
The insertion loss on the W filter side may increase, but if it is easy to keep the frequency intervals between them constant, such deterioration of the insertion loss can be suppressed.

In the surface acoustic wave device shown in FIG. 26, preferably, the center frequency f of the pass band of the multi-electrode SAW resonator filter 61 as the first SAW filter is used.
₀₁ and the center frequency f _{02 of} the second SAW filter 62 are expressed by the following equation (1)

[0078]

(Equation 3)

It is configured to satisfy. This will be described based on specific experimental examples. FIG. 28 shows 900 MHz
The experimental results of the film thickness h of the electrode made of Al and the ratio bandwidth of the amplitude characteristic to the ratio h / λ of the wavelength λ of the electrode in the three-electrode vertical coupling SAW resonator filter in the band are shown. From FIG. 28, it can be seen that when the film thickness h of the electrode is increased, the stop band width of the reflector of the resonator filter is expanded and the specific band width can be expanded.

36 ° Y-X LiTaO as a piezoelectric substrate
_{When 3} is used, in the longitudinally coupled SAW resonator filter,
In order to obtain a practically sufficient specific bandwidth of 3.3% for mobile phones, the electrode film thickness ratio h / λ is

[0081]

(Equation 4)

It is necessary to satisfy. On the other hand, the electrode film thickness ratio h
When / λ is increased, the pass band overlaps with the stop band on the low frequency side or the high frequency side, and there is a problem of insufficient attenuation in these regions. Therefore, the specific bandwidth is 6.9.
% Is not desirable, and the electrode film thickness ratio h /
λ is

[0083]

(Equation 5)

It is desirable to satisfy the above condition.

In the surface acoustic wave device of the present invention, in order to form two SAW filters on the same piezoelectric substrate, it is desirable from the viewpoint of workability that the electrode film thicknesses are the same. However, the first SAW filter and the second SAW filter
Since the SAW filter has a different pass band, the wavelength of the surface wave is also different. Therefore, if the electrode film thickness is the same, the electrode film thickness ratio h / λ of each filter will be different.

The center frequency of the first SAW filter is f ₀₁ , the wavelength λ ₁ , the center frequency of the second filter is f ₀₂ ,
When the wavelength is λ ₂ , there is a relation of λ ₂ > λ ₁ . That is, λ ₂ is the largest when h / 0.06,
₁ is the smallest when h / 0.10. At this time, the frequency ratio of the two filters becomes maximum, and the ratio of the wavelengths becomes λ ₁ / λ ₂ = 3/5.

On the same piezoelectric substrate, the wavelength λ and the reciprocal 1 / f of the frequency have a proportional relationship. Therefore, between the center frequency of the first filter and the second SAW filter,

[0088]

(Equation 6)

It is only necessary to have the relationship of. On the other hand, 2
The wider the frequency difference of the pass bands of the SAW filters, the higher the impedance of the pass band of the second SAW filter of the first SAW filter. This impedance is determined by the capacitance of the SAW filter and the stray inductance or stray resistance of the wiring.

FIG. 29 shows an impedance Smith chart on the IDT side outside the three-electrode SAW resonator filter. From FIG. 29, the impedance at the frequency smaller than 2/3 of the center frequency exists in the fourth quadrant on the impedance Smith chart.

If the impedance in the pass band of the other side, that is, the second SAW filter is in the fourth quadrant, the low impedance capacitor is used without adopting the method using the one-terminal SAW resonator connected in series in the present invention. The impedance can be increased while suppressing the deterioration of the insertion loss in the band as much as possible. That is, the first SA
The center frequency f ₀₁ of the pass band of the W filter and the second SA
The center frequency f _{02 of the} W filter is

[0092]

(Equation 7)

It can be seen that it is desirable to apply the structure of the present invention in the range of. Therefore, the first S
The center frequency f ₀₁ of the pass band of the AW filter and the second S
When the center frequency f ₀₂ of the AW filter satisfies the above equation (1), the impedance in the pass band of the second SAW filter of the first SAW filter becomes particularly low. Even in the case, by connecting one terminal pair SAW resonator in series,
The insertion loss of the W filter and the deterioration of VSWR can be suppressed as much as possible, and the deterioration of the insertion loss of the second SAW filter can also be suppressed.

[0094]

According to the invention described in claim 1, the one terminal pair S is provided between the connection point of the parallel connection of the first and second SAW filters having different pass bands and the first SAW filter.
Since the AW resonator and the capacitor are inserted in series, the insertion loss and VS on the first SAW filter side
It is possible to effectively suppress the deterioration of the WR and also suppress the deterioration of the insertion loss on the second SAW filter side which is the other side. Furthermore, it is possible to increase the amount of attenuation in the frequency region on the higher frequency side of the pass band while suppressing the deterioration of the insertion loss of the first SAW filter. Therefore, it is possible to provide a surface acoustic wave device compatible with multiple bands such as a mobile phone.

Further, as described in claim 2, the first S
The AW filter is configured by a multi-electrode type longitudinally coupled SAW resonator filter, and the one-terminal pair SAW resonator is provided on a plurality of IDTs including a pair of IDTs adjacent to a pair of reflectors of the SAW resonator filter. According to the connected configuration, in addition to the effect of the invention described in claim 1, the VSWR of the SAW resonator filter can be reduced, and thus the one-terminal pair S
It is possible to suppress the deterioration of the insertion loss due to the connection of the AW resonator.

Further, as described in claim 3, the first and second SAW filters are respectively formed by using the piezoelectric substrate, and the capacitor element is the first and second SAW filters.
When the filter is configured on one of the piezoelectric substrates, the capacitance value of the capacitor element can be easily changed in addition to the effect of the invention according to claim 1 or 2. The capacitance value can be changed easily and inexpensively as compared with the case where a capacitor is built in the substrate. Furthermore, when packaging a surface acoustic wave device, since the capacitor element is formed on the piezoelectric substrate, it is often unnecessary to change the package even if the capacitance value is changed. The package can be made common, and the cost of the structure in which the surface acoustic wave device is packaged can be reduced.

In addition, conventionally, two Ss having different pass bands are used.
In the surface acoustic wave device using the AW filter, it was necessary to form all the input / output electrodes of the SAW filter, that is, the four electrodes in the package material, whereas the capacitor element is used as the SAW filter as described above. By forming them on the same piezoelectric substrate, the number of electrodes to be formed on the packaging material can be set to three, which can further reduce the size of the package. Or,
On the contrary, by increasing the number of electrodes for grounding, it is possible to strengthen the grounding and suppress the deterioration of the attenuation amount due to the direct wave of the SAW filter.

Further, in the invention described in claim 4, since the first and second SAW filters are formed by using the same piezoelectric substrate, in addition to the effects of the invention described in claims 1 to 3, Since the assembly work of the surface acoustic wave device can be easily performed and the difference between the pass bands of the two SAW filters can be easily kept substantially constant, it is possible to manufacture the two SAW filters independently. In comparison, it is possible to reduce the influence of variations in characteristics.

In the invention described in claim 5, since the center frequencies of the first and second SAW filters are constituted so as to satisfy the above-mentioned expression (1), they are used as, for example, bandpass filters for mobile phones. In this case, it is possible to obtain a practically sufficient ratio bandwidth, and it is possible to sufficiently secure the amount of attenuation in the stop band existing on the low frequency side or the high frequency side of the pass band.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional surface acoustic wave device in which two SAW filters having different pass bands are connected in parallel.

FIG. 2 is a circuit diagram of a surface acoustic wave device according to a prior art which is not yet known and is formed by connecting two SAW filters having different pass bands in parallel.

FIG. 3 is a circuit diagram for explaining an example of a surface acoustic wave device of the present invention.

FIG. 4 is a first S of the surface acoustic wave device shown in FIG.
The figure which shows the attenuation amount frequency characteristic of an AW filter.

5A and 5B are impedances of a terminal on a side including two outer IDTs and a terminal on a central IDT side of the first SAW filter in the surface acoustic wave device shown in FIG. 3, respectively. The figure which shows a Smith chart.

6 is a first SAW in the surface acoustic wave device shown in FIG.
The figure which shows the attenuation amount frequency characteristic of a filter.

7 (a) and (b) are respectively 2 in the second SAW filter in the surface acoustic wave device shown in FIG.
The figure which shows the impedance Smith chart of the terminal of the side containing one outer IDT, and the terminal of the center IDT.

8A is an impedance Smith chart when a 3.5 pF capacitor element is connected in series to the output side terminal of the first SAW filter in the surface acoustic wave device shown in FIG. 3, FIG. ) Is one terminal pair S at the output side terminal of the first SAW filter in the surface acoustic wave device shown in FIG.
The figure which shows the impedance Smith chart at the time of connecting an AW resonator and further connecting the 8 pF capacitor element in series.

9 is a diagram showing attenuation-frequency characteristics when a one-terminal pair SAW resonator is connected in series to the output side terminal of the first SAW filter of the surface acoustic wave device shown in FIG.

10 (a) and 10 (b) are impedance Smith charts when a one-terminal pair SAW resonator is connected in series to the output side terminal of the first SAW filter in the surface acoustic wave device shown in FIG. It is a figure which shows (a) the impedance Smith chart of the terminal by the side of a center IDT, and (b) shows the impedance Smith chart of the terminal by the side of an outer IDT.

FIG. 11 is a diagram showing attenuation-frequency characteristics on the first SAW filter side of the conventional surface acoustic wave device shown in FIG. 1.

12A and 12B are diagrams showing impedance Smith charts at a central IDT side terminal and an outer IDT side terminal of the first SAW filter of the surface acoustic wave device of FIG. 1, respectively.

FIG. 13 is a first SAW of the surface acoustic wave device shown in FIG.
The figure which shows the attenuation amount frequency characteristic and VSWR-frequency characteristic on the filter side.

14A and 14B are respectively a terminal on the IDT side in the center and an I on the outside of the surface acoustic wave device shown in FIG.
The figure which shows the impedance Smith chart in the terminal by the side of DT.

15 is a diagram showing attenuation frequency characteristics and VSWR-frequency characteristics on the second SAW filter side of the conventional surface acoustic wave device shown in FIG.

16 (a) and 16 (b) are impedance Smith charts of the terminal on the side including the outer IDT and the terminal on the center IDT side in the second SAW filter of the surface acoustic wave device shown in FIG. 2, respectively. FIG.

FIG. 17 is a diagram showing an attenuation frequency characteristic and a VSWR-frequency characteristic of the second SAW filter when the first and second SAW filters are simply connected in parallel.

18 (a) and 18 (b) are outer IDTs obtained by simply connecting the first and second SAW filters in parallel, respectively.
The figure which shows the impedance Smith chart in the terminal of the side containing, and the center IDT side terminal.

FIG. 19 is a schematic plan view for explaining an example of a specific electrode connection state of the surface acoustic wave device of the present invention.

FIG. 20: A one-terminal pair SAW resonator is connected in series to one electrode of the IDT at the center of the SAW resonator filter, and 15 pF
The figure which shows the attenuation amount frequency characteristic at the time of further connecting the said capacitor element.

21A and 21B are outside IDs of the SAW resonator filter having the configuration shown in FIG. 20, respectively.
The figure which shows the impedance Smith chart of the terminal on the side containing T, and the terminal on the side containing center IDT.

FIG. 22: One-terminal pair SAW resonator connected in series to one electrode of the IDT at the center of the SAW resonator filter, and 15 pF
2nd SAW
Attenuation amount frequency characteristic and VSWR of the first SAW filter when the filter is connected in parallel to the first SAW filter
-The figure which shows a frequency characteristic.

23 (a) and 23 (b) are respectively a terminal on the side including the IDT on the outer side of the first SAW filter and a side including the IDT on the center in the configuration when the characteristics shown in FIG. 22 are obtained. Showing the impedance Smith chart of the terminal of FIG.

FIG. 24 is a schematic plan view showing another example of the electrode connection structure of the surface acoustic wave device of the present invention, in which the first S is formed on the piezoelectric substrate.
The figure which shows the state in which the AW filter, the one-terminal pair SAW resonator, and the capacitor element are connected.

25 is a cross-sectional view for explaining an example of the surface acoustic wave device of the present invention configured by using the piezoelectric substrate shown in FIG.

FIG. 26 is a schematic plan view for explaining another structural example of the surface acoustic wave device of the present invention in which the first and second SAW filters are formed on the same piezoelectric substrate.

27 is a sectional view of a structure formed by packaging the surface acoustic wave device shown in FIG.

FIG. 28: Three-electrode vertical coupling SA in the 900 MHz band
The figure which shows the ratio bandwidth of the amplitude characteristic with respect to ratio h / (lambda) of the film thickness h of an Al electrode, and the electrode wavelength (lambda) in a W resonator filter.

FIG. 29 is a three-electrode type S when the results shown in FIG. 28 are obtained.
The figure which shows the impedance Smith chart of the IDT terminal outside the AW resonator filter.

[Explanation of symbols]

21 ... Surface acoustic wave device 22 ... 1st SAW filter 23 ... 2nd SAW filter 24 ... Parallel connection point 25 ... Capacitor element 26 ... One terminal pair SAW resonator 27 ... Inductance element 31 ... Surface acoustic wave device 32 ... 1 SAW filter 33-35 ... IDT 36, 37 ... Reflector 38 ... One terminal pair SAW resonator 39 ... Parallel connection point 40 ... Capacitor element 42 ... Inductance element 42 ... Second SAW filter 43-45 ... IDT 46, 47 ... Reflector 51 ... Surface acoustic wave element 52 ... Piezoelectric substrate 53 ... Three-electrode type SAW resonator filter (first SAW filter) 54-56 ... IDT 59a-59c ... Ground electrode 58 ... Input extraction electrode 60, 61 ... Reflector 62 ... One terminal pair SAW resonator 63 ... Capacitor 64 ... Connection electrode (parallel connection point) 71 ... Surface acoustic wave Device 75 ... Piezoelectric substrate on which first SAW filter is formed 81 ... Second SAW filter 82-84 ... IDT 85, 86 ... Reflector

Claims (5)

[Claims] 1. A surface acoustic wave device comprising a plurality of SAW filters connected to each other, the first SAW having a pass band in a relatively high frequency region.
A second SAW filter having a pass band in a relatively low frequency region and connected in parallel to the first SAW filter at a connection point on the input end side or the output end side; and the first SAW filter. Between the filter and the connection point, and between the capacitor element and the first SAW filter, the capacitor element having an impedance of ¼ or more of the termination impedance of the surface acoustic wave device. And a one-terminal pair SAW resonator configured to have an anti-resonance frequency on a higher frequency side than a pass band of the first SAW filter. 2. The first SAW filter is formed on both sides of a piezoelectric substrate, an odd number of interdigital transducers formed on the piezoelectric substrate, and a region in which the odd number of interdigital transducers are formed. A multi-electrode longitudinally coupled SAW resonator filter having a pair of reflectors and a plurality of interdigital transducers including a pair of interdigital transducers adjacent to the pair of reflectors.
The surface acoustic wave device according to claim 1, wherein the W resonators are connected in series. 3. The first and second SAW filters are each configured by using a piezoelectric substrate, and the capacitor element is on one of the piezoelectric substrates of the first and second SAW filters. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is configured according to claim 1. 4. The surface acoustic wave device according to claim 1, wherein the first and second SAW filters are formed by using the same piezoelectric substrate. 5. The piezoelectric substrate is 36 ° Y—X LiT.
If the center frequency of the pass band of the first SAW filter is f ₀₁ and the center frequency of the second SAW filter is f ₀₂ , and it is an aO ₃ substrate, then The surface acoustic wave device according to claim 4, wherein the surface acoustic wave device is configured to satisfy the relationship.