JP3175581B2 - Surface acoustic wave device - Google Patents

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 for a mobile communication device having two or more frequency bands.

[0002]

2. Description of the Related Art In recent years, the functions of mobile communication devices have been enhanced, and for example, a multi-band portable telephone having two or more communication systems has been studied. To realize such a mobile phone, a broadband bandpass filter that can cover two or more bands is required. However, it has been difficult to realize a low-loss and wide-band filter that can cover two or more bands with a single element.

[0003] Attempts have been made to construct a wideband bandpass filter by combining a plurality of bandpass filters into one component. For example,
Japanese Patent Application Laid-Open No. 4-16014 discloses a wide-band surface acoustic wave device formed by combining a plurality of band-pass filters as described above. The configuration of the surface acoustic wave device disclosed in the prior art will be described with reference to FIG.

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

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

In a mobile phone, transmission and reception are performed at different frequencies. In the surface acoustic wave device 1, the transmission-side band-pass filter and the reception-side band-pass filter of 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 of the SAs
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]

In the surface acoustic wave device 1, the SAW filters 2 and 3 having different pass band frequency characteristics as described above are used. In some cases, it is not always possible to prepare a device having an optimum impedance characteristic.

On the other hand, when the impedance in the pass band of the SAW filter 3 of the SAW filter 2 connected to the capacitor 5 as a reactance element is low,
In order to reduce the insertion loss, it was 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 increases. As a result, the VSWR in the pass band deteriorates, and the There is a problem that insertion loss is deteriorated.

Therefore, in the above prior art, an inductance element 6 is connected between the connection point 4 and the ground potential as a second reactance element in order to compensate for the deterioration of the VSWR in the pass band. 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 will be degraded. Therefore, in the configuration in which the inductance element 6 is connected, it is necessary to further connect an impedance matching reactance element in the SAW filter 3 as in the SAW filter 2 side. As a result, the number of impedance matching elements increases, and the circuit configuration becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and is intended to be implemented with a relatively small number of parts and a relatively simple circuit configuration, having less limitation on the impedance characteristics of the SAW filter used. , The deterioration of the insertion loss can be suppressed, and the VSW in the pass band can be reduced.
It is an object of the present invention to provide a surface acoustic wave device having a plurality of passband characteristics that can reduce R.

[0012]

According to a broad aspect of the present invention, there is provided a surface acoustic wave device comprising a plurality of SAW filters connected to each other. A first SAW filter in a frequency domain and a second SAW in a frequency range having a relatively low passband and connected in parallel to the first SAW filter at a connection point on an input end or an output end side. A filter, a capacitor element connected between the first SAW filter and the connection point, and having an impedance equal to or more than １ ／ of the terminal impedance of the surface acoustic wave device; Connected between the first SA and the filter.
There is provided a surface acoustic wave device including a one-port SAW resonator configured to be on a higher frequency side than a pass band of a W filter.

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 pair of reflectors formed on both sides of the region where the odd number of IDTs are formed, and a multi-electrode type vertically coupled SAW resonator filter, and adjacent to the pair of reflectors. A pair of I
There is provided a surface acoustic wave device in which the one-port 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 constituted by using a piezoelectric substrate, and the first and second SAW filters are provided with first and second capacitor elements. It is configured on one of the piezoelectric substrates of the two SAW filters.

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

According to a more specific aspect of the present invention, the first and second SAW filters are formed using the same piezoelectric substrate. Further, according to another specific aspect of the present invention, the piezoelectric substrate may include 36 ° Y-XL.
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)

A surface acoustic wave device configured to satisfy the above relationship is provided.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the structure of a surface acoustic wave device according to the present invention, a surface acoustic wave device which has been filed by the applicant of the present invention and which is related to the present invention but not yet known will be described. This will be described with reference to FIG.

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

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

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

However, since the transmission line 16 is connected to the first band-pass filter 12 having a relatively high pass-band frequency, when a transmission line having a desired line length is formed, the band-pass filter 12, and hence 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 incorporated in a surface acoustic wave device package, the width of the transmission line 16 needs to be extremely narrow 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 package is incorporated in the package as described above, the area and height of the package are increased, and there is a possibility that the cost may be increased.

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 The impedance in the pass band becomes low, and even if a one-port SAW resonator is used instead of the transmission line 16, the impedance does not become sufficiently high, and the deterioration of the insertion loss of the other party, that is, the SAW filter 13 is suppressed. There was also a problem that it was not possible.

That is, the inventors of the present application have made one terminal pair SA
In view of the above-mentioned problems in the surface acoustic wave device 11 using the W resonator 15, the surface acoustic wave device according to the present invention described above has been invented as a result of further studies in view of the above-described problems.

Next, the configuration of a surface acoustic wave device according to 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.
Are connected in parallel on the output side. That is, the first SAW filter 22 whose pass band is relatively high in the high frequency region is connected to the input terminal IN ₁ , and the input terminal IN _1
2nd 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 to 885 MHz, and the pass band of the second SAW filter 23 is 810 to 826 MHz. First and second S
Outputs of the AW filters 22 and 23 are connected at a connection point 24.

Further, between the first SAW filter 22 and the connection point 24, a capacitor 25 and a one-terminal SAW
The resonator 26 is connected. The capacitor 25 is configured to have an impedance equal to or more than ４ of the terminal impedance of the surface acoustic wave device 21. Also,
The one-port SAW resonator 26 is connected between the capacitor 25 and the first SAW filter 22 and has an anti-resonance frequency higher than the pass band of the first SAW filter 22. It is configured as follows.

In this embodiment, an 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, a portion surrounded by a broken line indicated by reference numeral 28 is incorporated in one package.

Since the surface acoustic wave filter device 21 is configured as described above, the first SAW filter 22
When it is necessary to increase the impedance in the pass band of the second SAW filter 23 on the side, not only the capacitor 25 but also the one-port 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 of VSWR in a pass band. Moreover, the second SAW filter 23
Of the insertion loss can be suppressed.

In addition, an increase in the insertion loss of the first SAW filter 22 can be suppressed, and the amount of attenuation on the higher frequency side than the pass band of the first SAW filter 22 can be increased.

The operation and effect of the surface acoustic wave filter device 21 will be described based on specific experimental examples. First and second S
AW filters 22 and 23 having characteristics shown in FIGS. 4 to 7 were used.

FIG. 4 shows that the center frequency of the pass band is 872.
FIG. 5 is a diagram illustrating an attenuation frequency characteristic of the first SAW filter 22 at 5 MHz. The characteristic indicated by B in FIG.
The attenuation amount on the vertical axis is obtained by expanding the characteristic indicated by the solid line A according to the expansion scale shown on the right side of the vertical axis.

FIGS. 5A and 5B are impedance Smith charts of the input terminal and the output terminal of the first SAW filter 22, respectively. FIG.
Represents the attenuation frequency characteristic of the second SAW filter 23 whose center frequency in the pass band is 818 MHz, and the solid line D
The characteristic indicated by is obtained by enlarging the characteristic indicated by the solid line C in accordance with the expansion scale indicated by the attenuation amount on the vertical axis on the right side of the vertical axis. FIGS. 7A and 7C are diagrams showing impedance Smith charts of the input and output terminals of the second SAW filter 23. FIG.

FIG. 8A shows a capacitor 2 of 3.5 pF.
5 is an impedance Smith chart viewed from the output side when No. 5 is connected in series to a first SAW filter 22. As apparent from a comparison between FIG. 5B and FIG. 8A, in FIG. 8A, the impedance at 818 MHz is increased by the connection of the capacitor. At the same time, the impedance near the pass band deviates significantly from 50Ω pure resistance to capacitive.

FIG. 9 shows attenuation frequency characteristics inside and outside the pass band when the one-port SAW resonator 26 is connected in series to the output side of the first SAW filter 22.
(A), (b) is an impedance Smith chart of the input side and the output side in that case. In FIG. 9, the curve indicated by the solid line F is obtained by enlarging the characteristic indicated by the solid line E according to an enlarged scale shown on the right side of the vertical axis.
In this case, as a one-terminal SAW resonator, an IDT having 130 pairs of electrode fingers, an electrode finger cross width of 60 μm, and a pitch between electrode fingers of 2.2 μm is a 36 ° Y-X LiTaO.
What was formed on the piezoelectric substrate consisting of ₃ was used.

A comparison between FIG. 5B and FIG. 10B shows that the impedance at 818 MHz is increased by the one-port SAW resonator 26 in FIG. 10B. Also, comparing FIG. 10A with FIG. 5A, in FIG. 10A, the deterioration of the insertion loss in the pass band of the first SAW filter 22 is suppressed, and the frequency of the first SAW filter 22 is higher than the pass band. It can be seen that the attenuation on the side is increased.

FIG. 8B is 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 the present embodiment, that is, from the connection point 24. . FIG. 8B is replaced with FIG.
Compared with FIG. 8A, the characteristic 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 impedance from 50Ω pure resistance to capacitance is suppressed to a small value.

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

Further, the first surface acoustic wave device 1
12 (a) and 12 (b) show impedance Smith charts on the input side and 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 attenuation frequency characteristics 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. FIG. In FIG. 13, a solid line K is a characteristic obtained by enlarging the characteristic shown by the solid line J on a scale shown on the right side of the vertical axis, and a broken line L is a diagram showing the VSWR-frequency characteristic. FIGS. 14A and 14B
FIG. 3 is a diagram showing an impedance Smith chart on the input side and the parallel connection point 24 side on the first SAW filter 22 side.

In this embodiment, a 7.5 nH impedance matching inductance element 27 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 in FIG. 13, an increase in loss due to insertion of a capacitor is suppressed. For example, in FIG. 11, the pass band width of attenuation of 3.1 dB, that is, the so-called 3.1 dB bandwidth is 32.
In contrast to 5 MHz, in FIG.
It was expanded. At the same time, the maximum value of the VSRW at 860 to 885 MHz in FIG.
It can be seen from FIG. 13 that it is 75, which is 1.3. Further, it can be seen that the attenuation in the frequency region on the higher frequency side than the pass band is large.

FIG. 15 shows the second S in the above embodiment.
FIG. 3 is a diagram illustrating attenuation frequency characteristics in the AW filter 23. In FIG. 15, a solid line N is obtained by enlarging the characteristic shown by the solid line M on the scale shown by the right side of the vertical axis, and a broken line O shows a VSWR-frequency characteristic. FIGS. 16A and 16B are diagrams showing impedance Smith charts on the input side and the parallel connection point 24 side of the second SAW filter 23. Further, a 7.5 nH impedance matching inductance element 27 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 apparent from a 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.

FIG. 17 is different from the present invention in that the first SAW filter 22 and the second SAW filter
Second SAW filter 2 having a configuration in which
3 shows the attenuation frequency characteristic. In FIG. 17, the solid line Q
Represents the characteristic indicated by the solid line P in which the attenuation on the vertical axis is enlarged on the scale shown on the right side of the vertical axis, and the broken line R indicates VS.
5 shows a WR-frequency characteristic. FIGS. 18A and 18B are diagrams showing impedance Smith charts on the input side and the output side in this case. As is apparent from FIG. 17, in this case, the insertion loss increases.

FIG. 19 is a schematic plan view of a surface acoustic wave filter device according to a second preferred embodiment of the present invention. FIG.
In the above, a multi-electrode type vertically coupled SAW resonator filter 32 is formed as a first SAW filter on a piezoelectric substrate 31 made of 36 ° YX LiTaO ₃ . That is, the SAW resonator filter 32 includes three IDTs 33 to
35. The IDTs 33 to 35 are alternately input-side IDTs or output-side IDTs along the surface wave propagation direction. Each IDT 33, 34, 35 is constituted by a pair of comb-shaped electrodes having electrode fingers interposed therebetween.
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 electrodes 3 and 35 is grounded, and the other comb electrode is an output terminal. Also, the central I
One comb-shaped electrodes of DT34 is grounded, the other comb electrode 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 a main part of the characteristic shown by the solid line S with the attenuation on the vertical axis being enlarged on a scale shown on the right side of the vertical axis.
21 (a) and 21 (b) show impedance Smith charts of the SAW resonator filter 32. FIG.
. 1 (a) is a characteristic at the terminal connected to the input terminal IN ₁ of the central IDT 34, FIG. 21 (b) of the outer IDT3
This is a characteristic at the output terminals 3 and 35.

On the output side of the SAW resonator filter 32,
A one-port SAW resonator 38 is provided. The one-port SAW resonator 38 is connected in series to the comb electrodes constituting the output terminals of the IDTs 33 and 35 such that the anti-resonance frequency is higher than the pass band of the SAW resonator filter 32. Have been.

The attenuation frequency characteristic of the configuration in which the one-port 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-port SAW resonator 38 and the connection point 3
9, a capacitor 40 is inserted in series. S
The overall impedance Smith chart of the configuration in which the one-port 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. Here, the capacitance of the capacitor 40 was 8 pF. Therefore, as is clear from FIG. 8B, the impedance at 818 MHz is higher than that in 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 configuration as the inductance 27 in the first embodiment. Also,
The second SAW filter 42 is connected to the input terminal IN _2, the SAW filter 42 of the second is connected in parallel with the SAW filter 32 at 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.
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 according to the present embodiment is configured as described above, the same effect as the surface acoustic wave filter device according to the first embodiment is exerted. In addition, SAW
The filter 32 is constituted by a multi-electrode type longitudinally coupled SAW resonator filter, and is connected in series to a one-port SAW resonator 38. The effect of this configuration will be described below.

FIG. 20 shows one terminal pair S opposite to the above configuration.
This is the attenuation-frequency characteristic of the SAW filter 32 when the AW resonator 38 is connected in series to one of the comb electrodes of the central IDT 34, and then a capacitor having a capacitance of 15 pF is connected. FIGS. 21A and 21B are impedance Smith charts on the input side and the output side in this case.
As is clear from FIG. 21B, the impedance at 818 MHz is 818 MHz shown in FIG.
Almost coincides with the impedance at.

Further, the SAW when the second SAW filter 42 is connected in parallel to the configuration 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 attenuation indicated by the solid line U on the scale shown on the right side of the vertical axis,
The broken line W indicates the VSWR in the pass band.

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

When FIG. 22 and FIG. 13 are compared, FIG.
In, the increase in insertion loss is suppressed, for example, 3.1.
The dB bandwidth is 30.5 MHz in FIG. 22, but is expanded to 33.3 MHz in FIG. Similarly,
It can be seen that the deterioration of the VSWR is suppressed as much as possible.

This corresponds to 86 of the one-port SAW resonator 38.
0 to 880 MHz and the first S
860 of the output 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 the one made of iTaO ₃ was used, the invention is not limited to this. Other piezoelectric single crystals such as LiNbO ₃ or piezoelectric ceramics such as lead zirconate titanate-based piezoelectric ceramics, or insulating substrates or piezoelectric An appropriate piezoelectric substrate formed by forming a piezoelectric thin film on a conductive 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 according to the present invention, in which a first SAW filter, a one-port SAW resonator, and a capacitor are formed on the same substrate. Here are some examples.

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

In FIG. 24, 59a, 59b, 59c
Are extraction electrodes for connecting to the ground potential. Reflectors 60 and 61 are provided on both sides of the region where the IDTs 54 to 56 are provided in the surface wave propagation direction. The connection point 57 has a one-port SAW resonator 62.
Is connected. Also, one-port SAW resonator 62
Is connected to a capacitor 63.

The capacitor 63 is constituted by a pair of comb electrodes in FIG. The other comb electrode of the capacitor 63 is connected to the connection electrode 64. The connection electrode 64 forms 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 a piezoelectric substrate for forming a 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 incorporated in a 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 an insulating ceramic such as alumina or a synthetic resin. In FIG. 25, the package body 72 has a structure in which frame-shaped package members 72b and 72c each having an opening are stacked on a base plate 72a and bonded together. 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 SAW resonator, and a capacitor on the same surface, and a piezoelectric substrate 75 constituting a second SAW filter are fixed with an adhesive or the like.

The electrode terminals of the SAW filter on the piezoelectric substrates 52 and 75 are led out by wires 76 and 77 made of metal and are electrically connected to lead electrodes formed on the package body 72. Further, the sealing material 73 can be made of ceramic, metal, or the like. In this case, the piezoelectric substrate 5
An extraction electrode from which the SAW filter formed on the second and second electrodes 75 is extracted may be appropriately formed.

As shown in FIG. 25, the package body 72
A surface acoustic wave device of the present invention can be incorporated in a package including a sealing member 73 and a band-pass filter having a plurality of pass bands capable of exhibiting the above-described effects as a single component. Can be configured.

In the surface acoustic wave device 51 shown in FIG.
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 and the cross width of the interdigital electrode. Therefore, as shown in FIG. 25, when applied to a structure in which a piezoelectric substrate 52 having a capacitor formed on the surface is inserted into a package, it is necessary to change the dimensions of the package in accordance with a change in the capacitance value of the capacitor. Absent. That is, since the packages 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 of the input / output electrodes of the two SAW filters, ie, 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 can be reduced to three on one SAW filter side. Therefore, the size of the package can be further reduced. Or, conversely,
Since the number of electrodes for grounding can be increased, the grounding is strengthened, so that the deterioration of the amount of attenuation due to the direct wave of the SAW filter can be suppressed.

FIG. 26 is a schematic plan view showing an example in which the surface acoustic wave element 51 shown in FIG. 24 is developed and a 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 those in 1 are denoted by the same reference numerals.

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

The second SAW filter 81 has three IDs.
T82 to T84. Reflectors 85 and 86 are provided on both sides of the region where the IDTs 82 to 84 are provided in the surface wave propagation direction.
Are formed. One of the comb electrodes of the center IDT 83 of the second SAW filter 81 is connected to the connection electrode 64 described above.
, And the other comb electrode is connected to the ground extraction electrode 87a. Also, the outer IDT8
One of the comb electrodes 2 and 84 is connected to the input lead electrode 8.
7b, and the other comb electrode is connected to ground extraction electrodes 87c and 87d.

In the example shown in FIG. 26, all of the first and second SAW filters, capacitors, and one-port 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 main body 72, so that the working 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 interval between the pass bands of the SAW filters almost constant, so that the two SAW filters can be easily maintained.
Compared to a case where the W filters are manufactured independently, variations in characteristics can be reduced. In other words, when the frequency difference between them becomes smaller, the first higher frequency side
, The impedance in the pass band of the second SAW filter is low,
The insertion loss on the W filter side may increase, but if it is easy to make the frequency interval between them easy, 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 given by the following equation (1).

[0078]

(Equation 3)

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

As a piezoelectric substrate, 36 ° YX LiTaO
_When using ₃ , the longitudinally coupled SAW resonator filter
In order to obtain a practically sufficient ratio bandwidth of 3.3% for a mobile phone, the electrode film thickness ratio h / λ is as follows:

[0081]

(Equation 4)

It is necessary to satisfy the following. 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 a shortage of attenuation in these regions becomes a problem. Therefore, the fractional 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 following.

By the way, 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 thickness is the same. However, the first SAW filter and the second
Since the pass band is different from that of the above SAW filter, the wavelength of the surface wave is also different. Therefore, when the electrode thickness is the same, the electrode thickness ratio h / λ of each filter is 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 ,
If you have a wavelength λ _2, λ _2> λ ₁ of the relationship. That is, λ ₂ is largest when h / 0.06, and λ _2
1 is smallest when h / 0.10. At this time, the frequency ratio between the two filters is the largest, and the ratio of the wavelengths is λ ₁ / λ ₂ = 3/5.

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

[0088]

(Equation 6)

It is only necessary that the following relationship be satisfied. On the other hand, 2
As the frequency difference between the pass bands of the SAW filters becomes wider, the impedance of the first SAW filter in the pass band of the second SAW filter becomes higher. 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 a frequency smaller than 2/3 of the center frequency exists in the fourth quadrant on the impedance Smith chart.

If the impedance in the other party, that is, in the pass band of the second SAW filter is in the fourth quadrant, the method of using a one-port SAW resonator connected in series in the present invention is not used, and a low impedance capacitor is used. 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 within a certain range. 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 this case, by connecting the one-port SAW resonator in series, the first SA
The insertion loss of the W filter and the deterioration of the VSWR can be suppressed as much as possible, and the deterioration of the insertion loss on the second SAW filter side can also be suppressed.

[0094]

According to the first aspect of the present invention, the one-terminal pair S is connected 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 on the first SAW filter side and VS
The deterioration of the WR can be effectively suppressed, and the deterioration of the insertion loss on the side of the second SAW filter which is the partner can also be suppressed. Furthermore, it is possible to increase the amount of attenuation in a frequency region higher in frequency than the passband while suppressing the insertion loss of the first SAW filter. Accordingly, it is possible to provide a multi-band surface acoustic wave device such as a mobile phone.

Further, as described in claim 2, the first S
The AW filter is constituted by a multi-electrode type longitudinally coupled SAW resonator filter, and a one-terminal pair SAW resonator is provided to 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 first aspect, the VSWR of the SAW resonator filter can be reduced, and therefore, the one-port S
It is possible to suppress the deterioration of the insertion loss due to the connection of the AW resonator.

Further, the first and second SAW filters are each formed by using a piezoelectric substrate, and the capacitor elements are formed by the first and second SAW filters.
If the filter is formed 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 described in 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. Further, when the surface acoustic wave device is packaged, since the capacitor element is formed on the piezoelectric substrate, it is often unnecessary to change the package even when the capacitance value is changed. Thus, the package can be shared, and the cost of the structure in which the surface acoustic wave device is packaged can be reduced.

In addition, conventionally, two S bands having different passbands are used.
In the surface acoustic wave device using the AW filter, all of the input / output electrodes of the SAW filter, that is, four electrodes had to be formed on the package material, but the capacitor element was replaced with the SAW filter as described above. By forming them on the same piezoelectric substrate, it is possible to reduce the number of electrodes to be formed on the package material to three, thereby further reducing the size of the package. Or,
Conversely, by increasing the number of grounding electrodes, grounding can be strengthened and deterioration of the attenuation due to direct waves of the SAW filter can be suppressed.

Further, according to the fourth aspect of the present invention, since the first and second SAW filters are formed using the same piezoelectric substrate, in addition to the effects of the first to third aspects of the present invention, Since the work of assembling the surface acoustic wave device can be easily performed, and the difference between the pass bands of the two SAW filters can be kept almost constant, the two SAW filters are manufactured independently. In comparison, the influence of the variation in characteristics can be reduced.

According to the fifth aspect of the present invention, since the center frequencies of the first and second SAW filters are configured to satisfy the above-described equation (1), they are used, for example, as band filters for mobile phones. In this case, a practically sufficient fractional bandwidth can be obtained, and it is possible to sufficiently secure the amount of attenuation in a stop band existing on the low frequency side or the high frequency side of the pass band.

[Brief description of the 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 related 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 illustrating an example of a surface acoustic wave device according to the present invention.

FIG. 4 is a view showing a first S in the surface acoustic wave device shown in FIG. 3;
The figure which shows the attenuation amount frequency characteristic of an AW filter.

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

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

FIGS. 7A and 7B are diagrams respectively showing 2nd SAW filters in the surface acoustic wave device shown in FIG. 3;
The figure which shows the impedance Smith chart of the terminal of the side which contains this outside IDT, and the terminal of the center IDT.

FIG. 8A is an impedance Smith chart when a 3.5 pF capacitor element is connected in series to an output terminal of a first SAW filter in the surface acoustic wave device shown in FIG. 3; ) Indicates a one-terminal pair S to the output 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 an 8 pF capacitor element in series.

9 is a diagram showing attenuation frequency characteristics when a one-terminal SAW resonator is connected in series to an output terminal of a first SAW filter of the surface acoustic wave device shown in FIG. 3;

FIGS. 10A and 10B are impedance Smith charts when a one-port SAW resonator is connected in series to an output terminal of a first SAW filter in the surface acoustic wave device shown in FIG. 3; 5A is a diagram showing an impedance Smith chart of a terminal on the center IDT side, and FIG. 5B is a diagram showing an impedance Smith chart of a terminal on the outer IDT side.

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;

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

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.

14 (a) and (b) respectively show a terminal on the center IDT side and a terminal on the outer side of the surface acoustic wave device shown in FIG. 2;
The figure which shows the impedance Smith chart in the terminal of DT side.

FIG. 15 is a diagram showing an attenuation frequency characteristic and a VSWR-frequency characteristic on the second SAW filter side of the conventional surface acoustic wave device shown in FIG. 2;

16A and 16B are impedance Smith charts of a terminal on the side including the outer IDT and a 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;

FIGS. 18 (a) and (b) show outer IDTs when the first and second SAW filters are simply connected in parallel, respectively.
The figure which shows the impedance Smith chart in the terminal of the side which contains, 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 shows a one-port SAW resonator connected in series to one electrode of the center IDT of a SAW resonator filter, and a 15 pF
FIG. 9 is a diagram showing attenuation frequency characteristics when the capacitor element of FIG.

21 (a) and (b) are outer IDs of a SAW resonator filter having the characteristics shown in FIG. 20, respectively.
The figure which shows the impedance Smith chart of the terminal of the side containing T, and the terminal of the side containing IDT in the center.

FIG. 22 shows a one-port SAW resonator connected in series to one electrode of the center IDT of a SAW resonator filter, and a 15 pF
, And the second SAW
Attenuation frequency characteristics and VSWR of first SAW filter when filter is connected in parallel to first SAW filter
-The figure which shows a frequency characteristic.

FIGS. 23 (a) and (b) respectively show a terminal on the side including the IDT outside the first SAW filter and a side on the side including the central IDT in the configuration in which the characteristics shown in FIG. 22 are obtained. The figure which shows 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 a first S electrode is provided on a piezoelectric substrate.
The figure which shows the state in which the AW filter, the one-port SAW resonator, and the capacitor element are connected.

FIG. 25 is a cross-sectional view for explaining an example of the surface acoustic wave device according to the present invention constituted by using the piezoelectric substrate shown in FIG. 24;

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

FIG. 27 is a sectional view of a structure obtained by packaging the surface acoustic wave device shown in FIG. 26;

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

FIG. 29 shows a three-electrode type S obtained 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]

DESCRIPTION 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 filters 33 to 35 IDTs 36 and 37 reflector 38 one-port SAW resonator 39 parallel connection point 40 capacitor element 42 inductance element 42 second SAW filter 43 to 45 IDT 46 47: reflector 51: surface acoustic wave element 52: piezoelectric substrate 53: three-electrode SAW resonator filter (first SAW filter) 54 to 56: IDT 59a to 59c: ground electrode 58: input lead electrodes 60, 61 Reflector 62: One terminal pair SAW resonator 63: Capacitor 64: Connection electrode (parallel connection point) 71: Surface acoustic wave Apparatus 75: Piezoelectric substrate on which first SAW filter is formed 81: Second SAW filter 82 to 84: IDT 85, 86: Reflector

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03H 9/72 H03H 9/145 H03H 9/25

Claims (5)

(57) [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 passband in a relatively low frequency region and connected in parallel to the first SAW filter at a connection point on an input end or an output end side; and the first SAW. A capacitor element connected between the filter and the connection point and having an impedance equal to or more than 1/4 of the terminal impedance of the surface acoustic wave device; and between the capacitor element and the first SAW filter. And a one-port SAW resonator configured to have an anti-resonance frequency higher 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 where the odd number of interdigital transducers are formed. 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 resonator is connected in series. 3. The first and second SAW filters are each configured using a piezoelectric substrate, and the capacitor element is provided 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 as follows. 4. The surface acoustic wave device according to claim 1, wherein the first and second SAW filters are formed using the same piezoelectric substrate. 5. The method according to claim 1, wherein the piezoelectric substrate is a 36 ° YX LiT.
_aO-3 denotes a substrate, and f ₀₁ the center frequency of the passband of the first SAW filter, the center frequency of the second SAW filter and f _02, Equation 1] The surface acoustic wave device according to claim 4, wherein the surface acoustic wave device is configured to satisfy the following relationship.