JP2001308676A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an easily manufacturable band-pass type surface acoustic wave(SAW) filter capable of enhancing steepness in filter property between the passband and the stopband. SOLUTION: The filter has a ladder-type circuit comprising series arm resonators 4, 6 connected between input and output terminals IN, OUT and parallel arm resonators 3, 5, 7 connected between the series arm resonators and a reference potential, where the antiresonant frequencies of the parallel arm resonators 3, 5, 7 are substantially matched with the resonant frequencies of the series arm resonators 4, 6. In addition, the antiresonant frequency of at least one of the parallel arm resonators 3 is set to be inside the stop band of reflectors 3b, 3c and the spurious component is set outside the stopband to obtain the steepness in filter property from the passband to the stopband.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a band-pass SAW filter using a plurality of surface acoustic wave (hereinafter, SAW) resonators, and more particularly to a SAW filter having a ladder-type circuit configuration.

[0002]

2. Description of the Related Art A plurality of SAs are used as band-pass filters.
A SAW filter in which a ladder-type circuit is configured using a W resonator is known (for example, Japanese Patent Application Laid-Open No. 56-1976).
No. 5, JP-A-5-183380, etc.). In this type of SAW filter, it is strongly required to increase the amount of attenuation in a stop band near a pass band. In recent years, for example,
In a communication device such as a mobile phone, an interval between a transmission frequency and a reception frequency has become extremely narrow in order to enhance radio wave use efficiency. Therefore, in order to increase the selectivity, the appearance of a bandpass filter having a steeper filter characteristic between the passband and the stopband is desired.

[0003] Japanese Patent Application Laid-Open No. 9-55640 discloses a SAW filter satisfying the above demand. The SAW filter described in the prior art will be described with reference to FIG.

In the SAW filter 101, the surface substrate 10
2 are provided with one-port SAW resonators 103 to 107. Each one-port SAW resonator 103 to 107
Is an interdigital transducer (ID
T) 103a to 107a, each having IDT 10
Grating type reflectors 103b, 103c to 107b, 1 having a plurality of electrode fingers on both sides of 3a to 107a.
07c.

[0005] The SAW filter 101 is connected to an input terminal IN and an output terminal OUT. A series arm is formed between the input terminal IN and the output terminal OUT.
The SAW resonators 104 and 106 are connected as series arm resonators. On the other hand, between the series arm and the reference potential,
Three parallel arms are formed, that is, the SAW resonators 103, 105, and 107 are respectively connected between the series arm and the reference potential to form a parallel arm resonator.

The anti-resonance frequencies of the parallel arm resonators, ie, the SAW resonators 103, 105, 107, are configured to match the resonance frequencies of the series arm resonators, ie, the SAW resonators 104, 106.

In the SAW filter 101, the IDT of the SAW resonators 104 and 106 as the series arm resonators
With respect to the gap between the reflectors 104a and 106a and the reflectors 104b and 104c or the reflectors 106b and 106c, the SAW resonators 103, 105,
The substantial gap at 107 is increased or decreased. Therefore, spurious generated between the resonance frequency and the antiresonance frequency of the parallel arm resonator is generated between the resonance frequency of the parallel arm resonators 103, 105, and 107 and the pass band of the SAW filter 101, or in series with the pass band. It is set between the anti-resonance frequency of the arm resonator and the attenuation in the vicinity of the pass band in the stop band on the lower frequency side or the higher frequency side of the pass band.

That is, by setting the distance between the IDT of the parallel arm resonator and the reflector so as to generate the spurious component in the parallel arm resonator, a filter in the frequency domain from the pass band to the stop band is set. It is possible to provide a bandpass filter having excellent selectivity by increasing the steepness of the characteristics.

[0009]

As described above, in the SAW filter described in Japanese Patent Application Laid-Open No. 9-55640,
By adjusting the gap, that is, the distance between the IDT and the reflector in the parallel arm resonator, the filter characteristics near the pass band are sharpened.

However, in the prior art described in Japanese Patent Application Laid-Open No. 9-55640, it is necessary to adjust the gap between the IDT and the reflector. Was. In the case of a high frequency filter, the interval between the electrodes becomes extremely narrow, and the production of the filter may become difficult due to frequent occurrence of electrode short-circuiting or the like.

In recent years, there has been a strong demand for a SAW filter having better selectivity. Therefore, various techniques for steepening filter characteristics in a frequency domain from a pass band to a stop band have been strongly demanded. ing.

Accordingly, it is an object of the present invention to provide a SAW filter having a ladder-type circuit configuration using a SAW resonator, in which the attenuation characteristic at the boundary between the pass band and the stop band is sharp without increasing the number of stages. It is an object of the present invention to provide a SAW filter which can be manufactured easily.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and a serial arm is formed between the input and output, and at least one serial arm is provided between the serial arm and a reference potential.
S having a ladder-type circuit configuration in which two parallel arms are configured
It relates to an AW filter.

The invention according to claim 1 has a ladder-type circuit configuration in which a series arm is formed between the input and output, and at least one parallel arm is formed between the series arm and a reference potential. And at least one of the series arms having an IDT
A series arm resonator composed of a port-type SAW resonator has an IDT in the parallel arm and reflectors provided on both sides of the IDT, and the antiresonance frequency is different from the resonance frequency of the series arm resonator. In a surface acoustic wave filter in which a parallel arm resonator composed of substantially matched one-port SAW resonators is disposed, an anti-resonance frequency of at least one of the parallel arm resonators is set to a stop band of the reflector. The surface acoustic wave filter is characterized in that it is set so as to fall within a range, and the spurious generated by the parallel arm resonator is set outside the stop band of the reflector.

According to a second aspect of the present invention, in the surface acoustic wave filter according to the first aspect of the present invention, the spurious is between a resonance frequency of the parallel arm resonator and a pass band of the surface acoustic wave filter. And the period of the electrode finger of the reflector is made smaller than the period of the IDT, and the position where the spurious appears is
The stop band frequency is lower than the stop band frequency of the parallel arm resonator.

According to a third aspect of the present invention, there is provided the surface acoustic wave filter according to the first aspect of the present invention, wherein a pass band of the surface acoustic wave filter and an anti-resonance frequency of the series arm resonator are provided. The parallel arm resonator is configured to generate spurious, and the electrode finger cycle of the reflector is made longer than the electrode finger cycle in the IDT, and the spur is stopped by the parallel arm resonator. It is characterized in that it is configured to appear on the higher frequency side than the band.

According to a fourth aspect of the present invention, at least two or more parallel arm resonators in which the spurious component is generated are arranged in the parallel arm, and the spurious generated by at least one parallel arm resonator is reduced. , And is configured to be generated in a frequency region different from the spurious region generated by another parallel arm resonator.

According to the fifth aspect of the present invention, at least 2
A plurality of parallel arm resonators, and a spurious generated by at least one parallel arm resonator is configured to appear on a higher frequency side than a pass band of the surface acoustic wave filter. The distance between the IDT and the reflector is selected so that the spurious of the resonator appears on the lower side than the pass band.

According to a sixth aspect of the present invention, there is provided a surface acoustic wave filter according to any one of the first to fifth aspects, and a package containing the surface acoustic wave filter and hermetically sealed. A surface acoustic wave filter, wherein an electrode connected to a ground potential of at least one of the parallel arm resonators is electrically connected to a ground electrode provided on a package by a plurality of bonding wires. Device.

[0020] In the surface acoustic wave filter device according to the present invention, preferably, at least one of the parallel arm resonators includes a plurality of electrodes connected to a ground potential. Are connected, and the plurality of bonding wires are electrically connected to different ground electrodes formed on the package.

According to an eighth aspect of the present invention, an electrode of at least one of the parallel arm resonators connected to a ground potential is connected to the ground electrode provided on the package by a plurality of bonding wires. At least one of the bonding wires is connected to the ground electrode near the input side of the plurality of ground electrodes of the package, and the other bonding wire is connected to the ground electrode near the output side. It is characterized by.

According to a ninth aspect of the present invention, there is provided the surface acoustic wave filter according to any one of the first to eighth aspects, further comprising a plurality of electrode pads for connection to the outside, and electrodes of the surface acoustic wave filter. The surface acoustic wave filter comprising: a bump formed of a conductive material formed on a pad; and a plurality of electrodes to which the surface acoustic wave filter is connected, and a package for hermetically sealing the surface acoustic wave filter. Are electrically connected by joining the bumps to the electrodes formed on the package.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be clarified below by referring to Reference Examples on which the present invention is based and non-limiting Examples of the present invention.

(First Reference Example) FIG. 1 is a schematic plan view for explaining a SAW filter according to a first reference example. The SAW filter 1 is configured using a rectangular surface wave substrate 2. The surface acoustic wave substrate 2 is 36 ° in this embodiment.
It is composed of a rotating Y-cut LiTaO ₃ piezoelectric substrate. However, the surface acoustic wave substrate 2 may be made of another piezoelectric single crystal or a piezoelectric ceramic such as PZT.

On the surface acoustic wave substrate 2, parallel arm resonators 3, 5, and 7 each composed of a one-port SAW resonator, and similarly, series arm resonators 4 each composed of a one-port SAW resonator. 6 are constituted. Each SAW resonator 3 ~
7 has IDTs 3a to 7a at the center,
Grating type reflectors 3b, 3c to 7b, 7c having a plurality of electrode fingers are provided on both sides of 3a to 7a.

The SAW filter 1 is connected to an input terminal IN and an output terminal OUT. A series arm is formed between the input terminal IN and the output terminal OUT, and the series arm resonators 4 and 6 are inserted into the series arm. On the other hand, three parallel arms are formed between the series arm and the reference potential. That is, the above-described parallel arm resonators 3, 5, and 7 are respectively connected between the series arm and the reference potential.

The IDT 3a of the SAW resonator 3 has one comb-shaped electrode connected to the connection electrode 8 so that the ID of the SAW resonator 4
T4a is connected to one of the comb electrodes. The connection electrode 9 is formed by connecting the other IDT electrode 4a to the IDT 4a.
5a and one of the IDTs 6a. The connection electrode 10 is an IDT
The other comb electrode 6a is electrically connected to one comb electrode 7a of the IDT 7a.

Each of the IDTs 3a, 5a and 7a has the other comb electrode connected to a reference potential. Therefore,
The SAW filter 1 of the present embodiment has a conventionally known ladder-type circuit configuration.

Each of the SAW resonators 3 to 7 and the connection electrode 8
The electrodes such as 10 to 10 can be formed by applying a metal material such as aluminum on the surface acoustic wave substrate 2 by an appropriate method. For example, the electrode structure shown in FIG. 1 can be formed by forming aluminum on the entire surface of the substrate 2 and using photolithography technology. Alternatively, these electrodes can also be formed by applying a conductive material such as aluminum to the surface acoustic wave substrate 2 using a mask by a method such as evaporation or sputtering.

FIG. 1 schematically shows the electrode structure of each of the SAW resonators 3 to 7, that is, the number and length of electrode fingers. Further, the anti-resonance frequencies of the parallel arm resonators 3, 5, and 7 are configured to match the resonance frequencies of the series arm resonators 4, 6. Therefore, the SAW filter 1 operates as a band-pass filter.

The feature of this embodiment is that the parallel arm resonators 3, 5,
7 is that the width of the outermost electrode finger of the IDT is smaller than the width of the other electrode fingers in the IDT. This will be described with reference to FIG.

As shown in FIG. 2, in the parallel arm resonator 3,
Among the plurality of electrode fingers of the IDT 3a arranged at the center, the electrode fingers 3a ₁ , 3 located on the outermost side in the surface wave propagation direction
The width of a _2, are smaller than the width of the other electrode fingers 3a ₃ in IDT3a.

In FIG. 2, one bus bar 3d of the IDT 3a is extended in the surface wave propagation direction and is connected to one bus bar of the reflectors 3b and 3c.
The bus bar of T3a and one of the reflectors 3b and 3c may be separated.

Although not clearly shown in FIG. 1, in the other parallel arm resonators 5 and 7, as in the parallel arm resonator 3, the width of the electrode fingers on both sides in the surface propagation direction in the center IDTs 5a and 7a is similar. And the width of the other electrode fingers in the IDT.

A description will be given of how the filter characteristics from the pass band to the stop band can be sharpened by changing the width of the electrode finger in the IDT as described above. SAW
The spurious component of the resonator is generated by discontinuity between the IDT and the reflector. Usually, a SAW resonator is obtained by forming an electrode made of a metal thin film such as aluminum on a surface acoustic wave substrate by a fine processing process such as photolithography. Therefore, both the IDT and the reflector have similar structures, and reflect surface waves.

Therefore, if an electrode finger having a partially different electrode finger width exists in the IDT, the phase of the electrode finger is disturbed by reflection of a surface wave on the electrode finger, and spurious is generated.
As in this reference example, the outermost electrode fingers 3a ₁ ,
The width of 3a _2, when smaller than the other widths of the electrode fingers 3a ₃ of IDT 3, a phase change of the reflected wave becomes small, IDT
The same effect as in the case where the gap between 3a and the reflectors 3b and 3c is narrowed can be obtained. That is, spurious components appear on the lower frequency side than the resonance frequency of the parallel arm resonator. Further, the frequency position of the spurious can be arbitrarily changed by changing the electrode finger width. Therefore, if the frequency position of the spurious is set between the resonance frequency of the parallel arm resonator and the pass band of the SAW filter 1, the steepness of the filter characteristic on the lower side of the pass band can be increased.

Further, since it is not necessary to narrow the gap between the IDT 3a and the reflectors 3b and 3c, the steepness of the filter characteristic on the lower side of the pass band can be increased without complicating the manufacturing process.

(Second Reference Example) SA according to a second reference example
The W filter is the same as the first reference example except that the structure of the electrode finger of the IDT in the parallel arm resonator is different. Therefore, by referring to the description of the structure of the SAW filter described with reference to FIG. 1, the description of the other structure of the SAW filter will be omitted.

In the SAW filter according to the second reference example,
The parallel arm resonator 3 has an electrode structure shown in FIG. FIG.
In the parallel arm resonator 3, among the plurality of electrode fingers of the IDT 3a, the electrode fingers 3a ₄ and 3a ₅ located on the outermost side in the surface wave propagation direction are the remaining electrode fingers 3a ₃ of the IDT 3a.
Is wider than the width. The bus bar 3d has a structure in which the bus bar of the IDT 3a and the bus bars of the reflectors 3b and 3c are common.
The bus bars of the reflectors 3b and 3c may be separated.

In the other parallel arm resonators 5 and 7, the central IDTs 5a and 7a are configured similarly to the IDT 3a of the parallel arm resonator 3. That is, IDT
The width of the outermost electrode fingers of 5a and 7a is made larger than the width of the remaining electrode fingers in the IDT.

As in the present embodiment, the parallel arm resonator 3
Outermost electrode finger 3a of the IDT 3a _Four, 3a_FiveThe width of I
DT3a remaining electrode fingers 3a_ThreeLarger than the width of
The phase change of the reflected wave increases, and the IDT 3a and the reflector 3
The same effect as when the distance between b and 3c is widened can be obtained.
You. In other words, the higher band than the anti-resonance frequency of the series arm resonator
Spurs occur on the side. This spur occurs
The frequency position is the outermost electrode finger 3 of the IDT 3a.
a_Four, 3a_FiveCan be arbitrarily adjusted depending on the width of.

Accordingly, the series arm resonators 4 and 6 (see FIG. 1)
And the parallel arm resonators 3 and 3 so that the above-mentioned spurious occurs between the anti-resonance frequency of the SAW filter 1 and the pass band of the SAW filter 1.
By making the width of the outermost electrode fingers of the IDTs 3a, 5a, and 7a larger than the width of the remaining electrode fingers of the IDTs, it is possible to enhance the steepness of the filter characteristics on the higher pass band side. it can. Also in the SAW filter of the present reference example, for example, by changing the width of the electrode finger in the IDT, the steepness of the filter characteristic on the higher frequency side than the pass band can be increased, so that the electrode interval can be constant. Variations in production and short-circuit failure of the electrodes can be suppressed, and the production process can be simplified as compared with the SAW filter described in JP-A-9-55640.

(Third Reference Example) The first and second reference examples are as follows.
The widths of the electrode fingers of the IDT in the parallel arm resonators 3, 5, and 7 are varied to steepen the filter characteristics from the pass band to the stop band. However, the width of the electrode fingers in the reflector may be varied. Similarly, the filter characteristics from the pass band to the stop band can be sharpened.

In the SAW filter according to the third reference example, the width of the electrode finger of the reflector in the parallel arm resonator is made different to achieve a sharp filter characteristic from the pass band to the stop band.

The SAW filter according to the third reference example is similar to the SAW filter 1 shown in FIG. 1 except for the structure of the reflector of the parallel arm resonator. Accordingly, the structure of the reflector will be described with reference to FIG. 4 on behalf of the parallel arm resonator 3 among the parallel arm resonators 3, 5, and 7.

As shown in FIG. 4, in the parallel arm resonator 3, grating reflectors 3b,
3c, the electrode finger 3b on the side closest to the IDT 3a among a plurality of electrode fingers of each of the reflectors 3b, 3c.
₁ , 3c _{1 is} the width of the remaining electrode fingers 3b of the reflectors 3b, 3c.
₂ , 3c ₂ .

Since the IDT 3a and the reflectors 3b and 3c have similar structures as described above, they reflect the surface acoustic waves. Therefore, if an electrode finger having a partially different electrode finger width is present in the reflector, the phase of the electrode finger is disturbed by reflection at the electrode finger, and spurious is generated.

Then, of the plurality of electrode fingers of the reflectors 3b and 3c, the electrode finger 3b ₁ , 3 closest to the IDT 3a.
The width of c ₁ when greater than the width of the remaining electrode fingers, the phase change of the reflected wave is increased, the same effect as widening the distance between the electrode fingers in the IDT is obtained. That is, spurious components are generated by the parallel arm resonator 3 on the higher frequency side than the anti-resonance frequency of the series arm resonator, and the frequency position of the spurious component is arbitrarily adjusted by the width of the electrode fingers 3b ₁ and 3c _1. Can be.

Therefore, by setting the spurious component to appear between the anti-resonant frequency of the series arm resonators 4 and 6 (see FIG. 1) constituting the ladder type filter and the pass band of the filter, The steepness of the filter characteristic on the high pass band side can be increased.

In the other parallel arm resonators 5, 7, the IDTs 5 of the reflectors 5b, 5c, 7b, 7c are similarly provided.
The width of the electrode finger on the side closest to a and 7a is made larger than the width of the remaining electrode fingers of the reflector.

Also in this embodiment, it is not necessary to adjust the gap between the IDT and the reflector.
The manufacturing process can be facilitated as compared with the method disclosed in Japanese Patent No. 5640.

In this embodiment, the width of the electrode fingers 3b ₁ , 3c ₁ on the side closest to the IDT 3a of the reflectors 3b, 3c is
Although the electrode fingers are made larger than the remaining electrode fingers 3b ₂ and 3c _{2 of the} reflector, the electrode fingers may be made smaller, thereby increasing the steepness of the filter characteristic on the lower side of the pass band.

(First and Second Embodiments) The SAW filter according to the first embodiment is the same as the SAW filter 1 of the first reference example, except that the structure of the parallel arm resonator is different. Therefore, for the configuration other than the parallel arm resonator, the description of the first reference example described with reference to FIG. 1 is used.

The structure of the parallel arm resonator in the SAW filter according to the first embodiment will be described with reference to FIG. The parallel arm resonators 5 and 7 have the same configuration as the parallel arm resonator 3.

In the parallel arm resonator 3 shown in FIG.
the electrode finger pitch of the plurality of electrode fingers 3a ₃ in a lambda
_IDT is the electrode finger 3b ₂ , 3c ₂ in the reflectors 3b, 3c.
1.02 times the pitch λ _IDT of With this structure, the spurious due to the reflection of the surface acoustic wave is lower than the stop band of the parallel arm resonator, and the filter characteristic on the low band side of the parallel arm resonator is sharpened.
The reason for this will be described below in comparison with the prior art described in JP-A-9-55640.

As described above, the reflection of surface acoustic waves
Generate spurs near the pass band and generate
When increasing the sharpness of the filter characteristics,
In the vicinity of the ground, the combined impedance of the main resonance and spurious
Parallel resonance occurs due to the impedance. This parallel resonance
The impedance characteristic determines the distance between the IDT and the reflector.
0.5λ_Ref(Λ_RefIs the electrode finger pitch of the reflector) or less.
, That is, described in JP-A-9-55640.
When the parallel arm resonator is configured according to the method of FIG.
As shown by the arrow A in FIG.
And the impedance jumps up.
Que A appears. Conversely, the gap is set to 0.5λ _RefThan
When the size is increased, as shown by an arrow B in FIG.
In addition, the impedance peak B appears at the high frequency side of the spurious.
It is.

As described above, when the impedance rises on the low band side or the high band side of the spurious, and high impedance peaks A and B appear, when the SAW filter 1 having the ladder-type circuit configuration is formed, Spike-like ripples appear on the surface, resulting in deterioration of attenuation. In particular, when the Q value of the spurious resonance is high, the influence of the high impedance peaks A and B increases, and a sufficient amount of attenuation may not be obtained.

The high impedance peaks A and B can be suppressed by reducing the Q value of spurious resonance. Therefore, if a resistance is added to the parallel arm resonator to increase the loss, the Q value can be reduced.
However, in that case, the Q value of the main resonance also becomes low, so that the filter characteristics deteriorate. In particular, in the ladder type filter, since the anti-resonance point of the parallel arm resonator is used as the pass band, if the filter characteristic near the anti-resonance point is deteriorated due to a decrease in the Q value, the insertion loss is greatly deteriorated.

Therefore, it is necessary to lower the Q value near the spurious resonance and increase the Q value near the anti-resonance frequency of the main resonance. In this embodiment, in order to realize the above condition, the above condition is realized by making the pitch ratio between the electrode fingers of the IDT and the reflector in the parallel arm resonator different. That is, as described above, by increasing the pitch between the electrode fingers of the IDT 3a as compared with the pitch between the electrode fingers of the reflectors 3b and 3c, the Q value is reduced near the spurious resonance and the Q value is reduced near the resonance frequency of the main resonance. It is possible to increase.

The cavity-type one-port SAW resonator is originally formed by reflectors provided on both sides of the IDT.
By confining the surface wave energy in the resonator,
High Q value is obtained. The reflectivity of the reflector is close to total reflection within a finite frequency range called a stop band, but outside the stop band, the reflectivity is low and the energy trapping efficiency is poor. Therefore, by setting the stop band frequency such that the anti-resonance frequency of the main resonance is located within the stop band and the spurious resonance is located outside the stop band, the above-mentioned high impedance Peaks can be suppressed.

On the other hand, the center frequency of the stop band is determined by the electrode finger pitch λ _Ref of the reflector, and the bandwidth of the stop band is determined by the reflectance of the electrode finger of the reflector and the width of the electrode finger. The resonance frequency and antiresonance frequency of the parallel arm resonator are determined by the electrode finger pitch λ _{IDT of the IDT} . Therefore, the electrode finger pitch λ of the IDT
By adjusting the ratio between the _IDT and the electrode finger pitch λ _Ref of the reflector, the resonance frequency or the anti-resonance frequency can be set at an arbitrary position with respect to the stop band.

In this embodiment, as described above, the IDT 3a
Is larger than the electrode finger pitch of the reflectors 3b and 3c, the resonance frequency of the parallel arm resonator 3 is lower than the stop band (higher frequency side).
, Whereby the high impedance peak A is suppressed. That is, FIG. 7B shows the impedance-frequency characteristics in the present embodiment, and FIG.
It can be seen that the high impedance peak A on the lower side than the pass band is suppressed as compared with the characteristic shown in FIG.

On the contrary, FIG. 8B shows that the electrode finger pitch λ _IDT of the _IDT 3a is narrower than the electrode finger pitch λ _Ref of the reflectors 3b and 3c as in the second embodiment shown in FIG. 4 shows impedance-frequency characteristics in the case. Also in this case, the frequency of the resonator moves to the higher stop band, and the spurious resonance deviates from the stop band,
It can be seen that the high impedance peak is suppressed.

FIG. 9 is a diagram for explaining in more detail the impedance characteristics near the spurious components generated by the parallel arm resonator. FIG. 9 shows an IDT 3a and reflectors 3b, 3
6 shows characteristics when a gap between the resonance frequency and the resonance frequency is reduced and a spurious is generated between the resonance frequency and the anti-resonance frequency. In FIG. 9, the solid line C represents the ratio of the electrode finger pitch of the IDT to the electrode finger pitch of the reflector of 1.02.
DT, ie, the gap is 0.33λ.
As the _IDT, a characteristic of setting how differently the electrode finger width of the IDT, a broken line D is the electrode finger pitch ratio 1.00, the gap so that 0.40Ramuda _IDT, the electrode of the IDT The dashed-dotted line E indicates the characteristics when the finger width is set to be different.
00, gap = 0.50λ _IDT so that IDT
5 shows characteristics when different electrode finger widths are set.

As is clear from FIG. 9, the solid line C and the broken line D
It can be seen from the impedance characteristics shown in (1) that the change in impedance of the resonator from the anti-resonance frequency to the resonance frequency increases. Further, when comparing the impedance change when the pitch ratio is set to 1.02 (solid line C) and when the pitch ratio is set to 1.0 (dashed line D), it can be seen that there is almost no difference in the steepness of the impedance change.

On the other hand, regarding the high impedance peak of the spurious, the characteristic shown by the solid line C when the electrode finger pitch ratio is 1.02 is smaller than the characteristic shown by the broken line D. Therefore, as shown by the solid line C, by setting the electrode finger pitch ratio to be larger than 1 and the gap to be smaller than 0.5λ, it is possible to suppress deterioration of the attenuation due to spurious while maintaining high steepness. You can see that.

FIG. 10 is a diagram showing impedance characteristics of a resonator when the spurious is generated on the higher frequency side than the anti-resonance frequency. When steepness is required on the higher frequency side than the anti-resonance frequency, the I-phase is set so that a spurious component appears on the higher frequency side of the anti-resonance frequency of the parallel arm resonator.
The electrode finger pitch ratio may be set to 1 or less so that the gap between the DT and the reflector is set to 0.5λ or more, and the upper limit of the stop band is located between the anti-resonance frequency and the spurious frequency.

The solid line F in FIG. 10 indicates the electrode finger pitch ratio = 0.98, the gap = 0.60λ _IDT , and the broken line G
Is: electrode finger pitch ratio = 1.00, gap = 0.65λ
_{The IDT} and the dashed-dotted line H show the characteristics when the electrode ratio pitch ratio is 1.00 and the cap is 0.50λ _IDT .

As is apparent from FIG. 10, also in this case, the dashed-dotted line H for the gap = 0.50λ _IDT
Compared with the characteristics shown by the solid line F, the electrode finger width in the IDT is made different to increase the gap and generate spurious.
In the impedance characteristic indicated by the broken line G, it can be seen that the sharpness of the impedance change from the anti-resonance frequency to the high frequency side is enhanced.

Further, comparing the solid line F with the broken line G, it is understood that the characteristic of the solid line F where the electrode finger pitch ratio is 0.98 can reduce the high impedance peak due to the above spurious.

FIG. 11 shows the SAW when the electrode finger pitch ratio is 1.02 in the parallel arm resonator 3 shown in FIG.
3 shows a frequency characteristic of the filter 1. The other parallel arm resonators 5 and 7 are configured to have the same electrode finger pitch ratio.

When a parallel arm resonator having a normal electrode finger pitch ratio = 1.00 is used, a high impedance peak occurs in the attenuation region on the lower side of the pass band as shown by the broken line I in FIG. However, it can be seen that by increasing the pitch ratio to 1.02, a high impedance peak can be suppressed, and the attenuation can be improved by about 3 dB.

FIG. 12 shows that the electrode finger pitch ratio in the parallel arm resonator 3 shown in FIG.
FIG. 9 is a diagram illustrating frequency characteristics of the SAW filter 1 when the frequency is set to 8; In the other parallel arm resonators 5 and 7, the electrode finger pitch ratio is set to 0.98.

The broken line J in FIG. 12 shows the characteristics when a parallel arm resonator having a normal electrode pitch ratio = 1.00 is used. As is clear from FIG. 12, the electrode finger pitch ratio is 1.
In the case of 00, as shown by the broken line J, unnecessary spurious based on the high impedance peak occurs in the attenuation region higher than the pass band, but in the present embodiment, the pitch ratio is 0.98. It can be seen that by reducing the value, the high impedance peak can be suppressed, and the attenuation can be improved by about 3 dB.

Therefore, as is clear from the above-described first and second embodiments, by adjusting the electrode finger pitch ratio between the IDT and the reflector in the parallel arm resonator, high steepness near the pass band is achieved. It can be seen that a filter characteristic having

(Third Embodiment) FIG. 13 is a schematic plan view for explaining a SAW filter according to a third embodiment of the present invention. In the SAW filter 21 of the present embodiment, five SAW resonators are formed on the surface acoustic wave substrate 22. That is, the three parallel arm resonators 23, 25, 27
And two series arm resonators 24 and 26. That is, between the input terminal IN and the output terminal OUT, the one-port SAW resonators 24 and 26 as a series arm resonator are provided.
Has been inserted. Further, the parallel arm resonators 23, 25, 27
Are connected between the series arm and the ground potential, respectively. Reference numerals 28 to 30 denote connection electrodes, respectively, which constitute a ladder-type circuit having the parallel arm resonators 23, 25, 27 and the series arm resonators 24, 26.

In each of the above-described embodiments, the same parallel arm resonator is used as the plurality of parallel arm resonators.
In the filter 21, the parallel arm resonators 23, 25, and 27 differ in the way of making the outermost electrode finger width of the IDT different from the other electrode finger widths. That is, the parallel arm resonator 25
The electrode finger widths in the IDT are different so that the gap between the _IDT 25 and the reflectors 25b and 25c becomes 0.56λ _IDT in the parallel arm resonator 2
In Nos. 3 and 27, the electrode finger widths in the IDT are different so that the gap becomes 0.42λ _IDT . The parallel arm resonators 23, 25, and 27 can be configured according to the first to fifth embodiments, respectively, except for the gap.

As for the other points, the SA shown in FIG.
The configuration is the same as that of the W filter 1. In a ladder type filter, when a plurality of parallel arm resonators are used, each parallel arm resonator can be individually designed. Therefore, the spurious introduced to steepen the filter characteristics described above can be provided at different frequency positions in each parallel arm resonator. Therefore, by slightly shifting the frequency position of the spurious in a plurality of parallel arm resonators, although the sharpness of the filter characteristic is slightly deteriorated, the high impedance peak due to the spurious can be suppressed effectively, Good damping characteristics can be obtained. Further, by making the spurious frequency different between the parallel arm resonators, it is possible to suppress a decrease in the yield due to a variation at the time of manufacturing.

In particular, when it is necessary to increase the attenuation near the pass band on both the high band side and the low band side of the pass band, the configuration of the present embodiment can be suitably used. That is, the electrode finger width in the IDT is made different so that the gap between the parallel arm resonators 23 and 27 becomes smaller than 0.5λ _IDT , such as 0.42λ _IDT , whereby the above-mentioned gap is lowered to a lower side than the pass band. generate spurious to increase steepness, while the gap of the parallel arm resonator 25 is larger than 0.5 [lambda _IDT as 0.56Ramuda _IDT, to increase the steepness on the high frequency side of the pass band , The steepness of the filter characteristics can be enhanced on both the high band side and the low band side of the pass band.

FIG. 14 shows the frequency characteristics of the SAW filter of this embodiment. For comparison, FIG.
4 shows the attenuation-frequency characteristics of a W filter. Note that the characteristics shown in FIG. 15 are obtained when the gap, electrode finger width, and pitch of all the parallel arm resonators are made equal, and the gap is set to 0.5λ _IDT . As is clear from the comparison between FIG. 14 and FIG. 15, the SAW filter according to the present embodiment can improve the attenuation by about 10 dB near the pass band.

(Fourth Embodiment) The fourth embodiment relates to a surface acoustic wave filter device in which the surface acoustic wave filter according to the present invention is housed in a package.

For comparison, a conventional surface acoustic wave filter device will first be described with reference to FIG. The surface acoustic wave filter device 31 has a structure in which a surface acoustic wave filter 101 shown in FIG. That is, the surface acoustic wave filter 101 is fixed to the bottom surface 32 a of the package 32. In the package 32, step portions 32b and 32c are formed on both sides of the bottom surface 32a. The electrodes 33a to 33c, 3 are provided on the step 32b, respectively.
4a to 34c are formed. Electrodes 33a to 33c,
34a to 34c are drawn out of the package 32 and are configured to be electrically connected to the outside.

The parallel arm resonator 10 of the SAW filter 101
One of the IDTs 103a of the third IDT 103a is connected to the electrode 33a by a bonding wire 35a. Electrode 33a
Is an electrode connected to the ground potential.

The connection electrode 108 is connected to the electrode 33b by the bonding wire 35b. One comb electrode of the IDT of the parallel arm resonator 105 is connected to the electrode 34a by a bonding wire 35c.
The electrode 34a is an electrode connected to the ground potential.

The connection electrode 110 is connected to the electrode 34b by a bonding wire 35d. On the other hand, one comb electrode of the IDT of the parallel arm resonator 107 is connected to the electrode 34c by the bonding wire 35e. The electrode 34c is an electrode connected to the ground potential.

The electrode 33b is an electrode connected to the input terminal, and the electrode 34b is an electrode connected to the output terminal. Therefore, in the SAW filter device 31, the five bonding wires 35a to 35e are connected to the electrodes 33a, 33b, 34a to 34c formed on the package.

FIG. 17 is a plan view for explaining a SAW filter device according to a fourth embodiment of the present invention. In the SAW filter device 41 of the present embodiment, the SAW filter 1 according to the first reference example is housed in a package 42. The package 42 is the package 3 described above.
It is configured similarly to 2. That is, step portions 42b and 42c having a height higher than the bottom surface 42a are provided on both sides of the bottom surface 42a.
Are formed, and the electrodes 43a to 43c are formed on the step portion 42b.
The electrodes 44a to 44c are respectively formed on the step portions 42c.

ID of parallel arm resonator 3 of SAW filter 1
Comb electrodes on the side connected to the ground potential of T are connected to the electrodes 43a, 43b by the bonding wires 45a, 45b.
c. That is, the comb electrode connected to the ground potential of the IDT is connected to the electrodes 43a and 43c connected to different ground potentials on the package 42 side by the two bonding wires 45a and 45b.

On the other hand, the connection electrode 8 is connected to an electrode 43b as an input electrode by a bonding wire 45c. The comb electrode on the side of the parallel arm resonator 5 connected to the ground potential of the IDT is a bonding wire 45.
By d and 45e, they are connected to different electrodes 44a and 44c connected to the ground potential, respectively. That is, by the two bonding wires 45d and 45e,
They are connected to different electrodes 44a and 44c connected to the ground potential formed on the package 42 side.

The connection electrode 10 is connected to an electrode 44b as an output electrode formed on the package 42 by a bonding wire 45f. Further, a comb electrode connected to the ground potential of the IDT of the parallel arm resonator 107 is connected to the package 4 by a bonding wire 45g.
It is connected to the electrode 44c connected to the ground potential formed on the second side.

As described above, when steep filter characteristics from the pass band to the stop band are used in the parallel arm resonator by using the above-mentioned spurious, the high impedance peak due to the spurious is reduced by the amount of attenuation near the spurious frequency. It appears remarkably when the value is small, and is suppressed as the amount of attenuation increases. The amount of attenuation lower than the pass band becomes maximum near the resonance frequency of the parallel arm resonator, and rapidly decreases when the distance from the resonance frequency increases.

Therefore, by bringing the spurious frequency close to the resonance frequency of the parallel arm resonator, a high impedance peak due to the spurious can be suppressed.
However, if the spurious frequency is lowered to make the spurious frequency close to the resonance frequency of the parallel arm resonator, the trap due to the spurious will fall off the shoulder of the pass band, and the effect of sharpening the filter characteristics will not be obtained. Therefore, it is necessary to increase only the resonance frequency of the main resonance.

On the other hand, it is known that the resonance frequency of a one-port SAW resonator is reduced by inserting an inductance in series with the one-port SAW resonator.
Further, in the SAW filter device, electrical connection to the package is usually made by a bonding wire made of Al, Au, or the like. However, inductance is inevitably added by the wiring bonding wire.

There is also an inductance due to the internal wiring of the package and an inductance due to the external circuit. Therefore, in order to increase the resonance frequency, it is necessary to reduce these inductances as much as possible.

The SAW according to the fourth embodiment shown in FIG.
The filter device 41 is characterized in that the inductance is reduced by devising a connection structure using bonding wires. This is shown in FIGS. 19 and 20.
This will be described with reference to FIG.

FIG. 19 is a circuit diagram showing an equivalent circuit including the inductance of the conventional SAW filter device shown in FIG. Here, since the inductance L1 of the bonding wire, the residual inductance L2 of the package 32, and the residual inductance L3 of the earth electrode of the external circuit are connected in series to the parallel arm resonator, the inductance La applied to the resonator is It is expressed by an equation.

La = L1 + L2 + L3 (1) On the other hand, FIG. 20 is a circuit diagram showing an equivalent circuit including the inductance of the SAW filter device of the embodiment shown in FIG.

Here, in the parallel arm resonators 3 and 5,
Each of the two bonding wires 45a, 45b and 45d, 45e is used to electrically connect to the ground potential. Therefore, the inductance L1 of the bonding wire and the residual inductance L2 of the package are inserted in parallel. Will be. Therefore, the inductance Lb applied to the parallel arm resonator in this case is expressed by the following equation.

Lb = (L1 + L2) / 2 + L3 (2) Therefore, as is clear from comparison between the equations (1) and (2), the embodiment shown in FIG. 17 reduces the inductance component. can do.

FIG. 22 shows the frequency characteristics of the conventional SAW filter device shown in FIG. 16, and FIG. 23 shows the frequency characteristics of the SAW filter device 41 according to the fourth embodiment shown in FIG. . As is clear from FIG. 22, in the conventional SAW filter device 31, although the steepness from the pass band to the stop band is enhanced by the generation of the spurious component, the attenuation is 16 dB due to the effect of the high impedance peak point caused by the spurious component. Stays on.

On the other hand, as is apparent from FIG. 23, in the SAW filter device according to the fourth embodiment, the spurious level is reduced as a whole by increasing the trap frequency due to the main resonance on the low frequency side. It can be seen that the attenuation in the stop band is improved by about 6 dB.

(Fifth Embodiment) FIG. 18 is a schematic plan view showing a modification of the SAW filter device according to the fifth embodiment. In the SAW filter device 51, the SAW filter 1 is fixed to the bottom surface 42a of the package 42. The comb electrodes connected to the ground potential of the IDT of the parallel arm resonator 3 are connected to the electrodes 43a and 44a connected to the ground potential formed on the package 42 side by bonding wires 55a and 55b. Further, the comb electrode connected to the ground potential of the IDT of the parallel arm resonator 5 is connected to the electrode 4 connected to the ground potential formed on the package 42 by the bonding wires 55c and 55d.
3c, 44a. Further, the comb electrode connected to the ground potential of the IDT of the parallel arm resonator 7 is connected to the electrode 4 connected to the ground potential formed on the package 42 by the bonding wires 55e and 55f.
3c, 44c. Other configurations are the same as those of the SAW filter device 41.

In this embodiment, each of the comb electrodes connected to the ground potential of the IDT of the parallel arm resonators 3, 5, 7 has two bonding wires 55a, 55b, 55c,
55d and 55e, 55f are electrically connected to different electrodes to be connected to the ground potential formed on the package 42 side.

FIG. 21 shows an equivalent circuit including the inductance of the SAW filter device 51. In the SAW filter device 21, the inductance of the parallel arm resonator is reduced by the wiring using the bonding wires. That is, by using two bonding wires for the comb electrode connected to the ground potential of the IDT of the parallel arm resonator as described above, and connecting each of the two bonding wires to a different package-side ground potential. The inductance of L1 + L2 + L3 is inserted in parallel into each parallel arm resonator. Therefore, the inductance Lc applied to the parallel arm resonator is Lc = (L1 + L2 + L
3) / 2. Therefore, the inductance can be reduced by half as compared with the conventional SAW filter device 31 shown in FIG.

FIG. 24 shows attenuation frequency characteristics of the SAW filter device 51 shown in FIG. As is clear from FIG. 24, as compared with the frequency characteristics of the fourth embodiment shown in FIG. The attenuation in the element band is shown in FIG.
It can be seen that the characteristics can be improved by about 10 db as compared with the characteristics of the conventional SAW filter device 31 shown in FIG.

(Sixth Embodiment) FIG. 25 shows a sixth embodiment of the present invention.
FIG. 3 is a cross-sectional view for explaining a SAW filter device according to the example of FIG.

In the SAW filter device 61, a package is constituted by the package substrate 62 and the cap 63. That is, the SAW filter 1 is housed in the internal space 64 formed by the package substrate 62 and the cap 63. Further, the SAW filter 1 is fixed to the package substrate 62 by a mounting method called a face-down method. That is, bumps 65a, 65b made of solder or the like are formed on the electrode pads 1a, 1b for connection to the outside of the SAW filter 1, and the SAW filters 65a, 65b are directed downward.
The SAW filter 1 is electrically connected to the package substrate 62 by disposing the filter 1 and joining the bumps 65a and 65b to the electrodes 66a and 66b formed on the package substrate 62. The electrode pads 1a, 1b
Indicates an electrode portion connected to the outside of the SAW filter device 1, and corresponds to, for example, a comb electrode connected to the ground potential of the parallel arm resonator or the connection electrodes 8 to 10 described above. In FIG. 25, the SA according to the first reference example is shown.
Although the W filter 1 is shown as a representative example, the SAW filter according to another embodiment of the present invention can be similarly fixed to the package substrate 62 in a face-down manner.

In the SAW filter 61 of the present invention, the package is connected to the package via the bumps 65a and 65b by the face-down method without using a bonding wire.
Since the electrical connection with the AW filter 1 is achieved, the inductance applied to the ground side of the parallel arm resonator can be made extremely small, whereby the resonance frequency of the parallel arm resonator can be increased. Therefore, it is possible to more effectively suppress the high impedance peak caused by increasing the steepness of the filter characteristic in the frequency domain from the pass band to the stop band due to spurious, and further increase the attenuation in the stop band. it can.

[0109]

In the surface acoustic wave filter according to the first aspect of the present invention, the anti-resonance frequency of at least one parallel arm resonator is set so as to fall within the stop band of the reflector. Since the spurs generated to enhance the steepness of the characteristics are set so as to be outside the stop band of the parallel arm resonator, the spurs to enhance the steepness of the filter characteristics without deteriorating the insertion loss. Can suppress high impedance peaks, and a sufficient amount of attenuation can be secured in the stop band.

According to a second aspect of the present invention, in the SAW filter according to the first aspect of the present invention, the spur is generated between the resonance frequency of the parallel arm resonator and the pass band of the SAW filter. And the period of the electrode finger of the reflector is made smaller than the period of the IDT,
Since the frequency position at which the above spurious appears is lower than the stop band frequency of the parallel arm resonator,
High impedance peaks caused by the spurious components for steepening the filter characteristics can be reliably suppressed, and a sufficient amount of attenuation can be ensured in the stop band.

According to the third aspect of the present invention, in the SAW filter according to the first aspect, the SAW
The spurious response of the parallel arm resonator is generated between the pass band of the filter and the anti-resonance frequency of the series arm resonator, and the electrode finger cycle of the reflector is greater than the electrode finger cycle of the IDT. The spurs are configured to appear higher than the stop band of the parallel arm resonator, so that the filter characteristics on the higher side of the pass band can be sharpened, and A sufficient amount of attenuation can be ensured in a stop band higher than the pass band.

According to the fourth aspect of the present invention, at least two or more parallel arm resonators that generate spurious for achieving the steepness of the filter characteristic are arranged in the parallel arm, and at least one parallel arm resonator is provided. The spurs generated by the arm resonator are configured to appear in a different frequency range from the spurs generated by other parallel arm resonators, so high impedance peaks due to spurious generation can be suppressed. In addition, it is possible to suppress a decrease in yield due to a variation during manufacturing.

According to the fifth aspect of the present invention, at least two parallel arm resonators are provided, and the spurious generated by at least one parallel arm resonator has a higher frequency band than the pass band of the SAW filter. The spurs generated by other parallel arm resonators are configured to appear on the side.
Since the distance between the IDT and the reflector is selected so as to appear on the lower side of the pass band, the above-mentioned spurious appears on both the lower side and the higher side of the pass band, and the filter appears in both of these areas. The steepness of the characteristics can be increased.

According to the sixth aspect of the present invention, in the SAW filter device in which the SAW filter is housed in the package, the electrode connected to the ground potential in at least one parallel arm resonator is formed by a plurality of bonding wires. Is electrically connected to the ground electrode provided in the parallel arm resonator, the inductance added in series to the parallel arm resonator can be reduced, thereby suppressing the high impedance peak due to the occurrence of the spurious noise. , The amount of attenuation in the stop band can be improved.

According to the seventh aspect of the present invention, a plurality of bonding wires are connected to the electrode connected to the ground potential in at least one parallel arm resonator.
Since the plurality of bonding wires are electrically connected to different ground electrodes formed on the package, the inductance added in series to the parallel arm resonator can be further reduced, and thereby the filter near the pass band can be reduced. Not only can the steepness of the characteristics be improved, but also high impedance peaks caused by the spurious components can be more effectively suppressed, and the attenuation in the stop band can be further increased.

According to the invention described in claim 8, the electrode connected to the ground potential in at least one parallel arm resonator is connected to the ground electrode provided on the package by a plurality of bonding wires. Since at least one of the plurality of bonding wires is connected to the ground electrode near the input side of the plurality of ground electrodes of the package and the other bonding wire is connected to the ground electrode near the output side, the inductance component is , The amount of attenuation in the stop band can be further increased.

In the SAW filter device according to the ninth aspect of the present invention, the SAW filter, a bump made of a conductive material formed on the electrode pad of the SAW filter, and
A plurality of electrodes to which the AW filter is connected, and
A package for hermetically sealing the W filter,
Since the SAW filter is electrically connected to the electrode of the package by bonding the bump to the electrode formed on the package, that is, the SAW filter is electrically connected to the electrode of the package in a face-down manner. Therefore, no bonding wire is required. Therefore, the inductance added to the parallel arm resonator can be made extremely small, and the attenuation in the stop band lower than the pass band can be further improved.

[Brief description of the drawings]

FIG. 1 is a schematic plan view illustrating a SAW filter according to a first reference example of the present invention.

FIG. 2 is a plan view for explaining a parallel arm resonator used in a first reference example of the present invention.

FIG. 3 is a plan view for explaining a parallel arm resonator used in a second reference example.

FIG. 4 is a plan view for explaining a parallel arm resonator used in a third reference example.

FIG. 5 is a plan view for explaining a parallel arm resonator used in the first embodiment.

FIG. 6 is a plan view for explaining a parallel arm resonator used in a second embodiment.

FIGS. 7A and 7B show the impedance characteristic and stop band of a SAW filter prepared for comparison, and the impedance characteristic and stop band of a parallel arm resonator used in the first embodiment, respectively. FIG.

FIGS. 8A and 8B are diagrams for explaining impedance characteristics and a stop band of a conventional one-port SAW resonator and a parallel arm resonator according to the second embodiment, respectively.

FIG. 9 is a diagram illustrating impedance-frequency characteristics of a parallel arm resonator used in the SAW filter according to the first embodiment.

FIG. 10 is a diagram illustrating impedance-frequency characteristics of a parallel arm resonator used in the SAW filter according to the second embodiment.

FIG. 11 is a diagram illustrating frequency characteristics of the SAW filter according to the first embodiment.

FIG. 12 is a diagram illustrating frequency characteristics of a SAW filter according to a second embodiment.

FIG. 13 is a schematic plan view of a SAW filter according to a third embodiment of the present invention.

FIG. 14 is a diagram illustrating frequency characteristics of a SAW filter according to a third embodiment of the present invention.

FIG. 15 is a diagram showing frequency characteristics of a conventional SAW filter.

FIG. 16 is a plan view illustrating an example of a conventional SAW filter device.

FIG. 17 is a plan view for explaining a SAW filter device according to a fourth embodiment of the present invention.

FIG. 18 is a plan view for explaining a SAW filter device according to a fifth embodiment of the present invention.

FIG. 19 is a diagram showing an equivalent circuit of a conventional SAW filter device.

FIG. 20 is a diagram showing an equivalent circuit of a SAW filter device according to a fourth embodiment of the present invention.

FIG. 21 is a diagram showing an equivalent circuit of a SAW filter device according to a fifth embodiment of the present invention.

FIG. 22 is a diagram showing frequency characteristics of the conventional SAW filter device shown in FIG.

FIG. 23 is a diagram illustrating frequency characteristics of the SAW filter device according to the embodiment illustrated in FIG. 17;

FIG. 24 is a view showing frequency characteristics of the SAW filter device of the embodiment shown in FIG. 18;

FIG. 25 is a sectional view of a SAW filter device according to a sixth embodiment of the present invention.

FIG. 26 is a plan view showing an example of a conventional SAW filter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... SAW filter 1a, 1b ... Electrode pad 2 ... Surface wave board 3,5,7 ... Parallel arm resonator 3a, 5a, 7a ... IDT 3b, 3c, 5a, 5b, 5c, 7a, 7c ... Reflector 4, Reference numeral 6: series arm resonator 4a, 6a IDT 21 SAW filter 22 surface wave substrate 23, 25, 29 parallel arm resonator 23a, 25a, 27a IDT 23b, 23c, 25b, 25c, 27b, 27c reflection Units 24, 26 ... series arm resonators 24a, 26a ... IDT 41 ... SAW filter device 42 ... packages 43a to 43c, 44a to 44c ... package electrodes 45a to 45g ... bonding wires 51 ... SAW filter devices 55a to 55f ... bonding wires 61: SAW filter device 62: Package substrate 63: Cap 65a, 65b: Bump 66a , 66b ... electrodes formed on the package

Claims (9)

[Claims] 1. A ladder-type circuit configuration wherein a series arm is formed between an input and an output, and at least one parallel arm is formed between the series arm and a reference potential. A series arm resonator comprising at least one one-port SAW resonator having a digital transducer has an interdigital transducer on the parallel arm and reflectors provided on both sides of the interdigital transducer, and 1-port SAW whose resonance frequency is substantially equal to the resonance frequency of the series arm resonator
In a surface acoustic wave filter in which a parallel arm resonator including a resonator is disposed, an anti-resonance frequency of at least one of the parallel arm resonators is:
The elasticity is set to be within the stop band of the reflector, and the spurious generated by the parallel arm resonator is set to be outside the stop band of the reflector. Surface wave filter. 2. The apparatus according to claim 1, wherein said spurious is generated between a resonance frequency of said parallel arm resonator and a pass band of a surface acoustic wave filter, and a period of an electrode finger of said reflector is interdigital. 2. The surface acoustic wave filter according to claim 1, wherein the position of the spurious is smaller than a stop band frequency of the reflector, and is smaller than a period of the transducer. 3. 3. A pass band of the surface acoustic wave filter;
It is configured such that spurious of the parallel arm resonator is generated between the anti-resonance frequency of the series arm resonator and
In addition, the period of the electrode finger of the reflector is made larger than the period of the electrode finger of the interdigital transducer, and the spurious is configured to appear on the higher frequency side than the stop band of the reflector. And
The surface acoustic wave filter according to claim 1. 4. The parallel arm resonator in which the spurious component is generated is arranged in at least two parallel arms, and the spurious generated by at least one parallel arm resonator is connected to another parallel arm resonance. The surface acoustic wave filter according to any one of claims 1 to 3, wherein the surface acoustic wave filter is configured to be generated in a frequency region different from the spurious generated by the element. 5. It has at least two parallel arm resonators,
The spurs generated by at least one parallel arm resonator are configured to appear higher than the pass band of the surface acoustic wave filter, and the spurious of the other parallel arm resonators is higher than the pass band. The surface acoustic wave filter according to any one of claims 1 to 4, wherein the surface acoustic wave filter is configured to appear on a low frequency side. 6. A surface-acoustic-wave filter according to claim 1, further comprising a package in which the surface-acoustic-wave filter is housed and hermetically sealed, wherein at least one of the parallel circuits is provided. A surface acoustic wave filter device wherein an electrode of the arm resonator connected to a ground potential is electrically connected to a ground electrode provided on a package by a plurality of bonding wires. 7. A plurality of bonding wires are connected to an electrode of at least one of the parallel arm resonators connected to a ground potential, and the plurality of bonding wires are electrically connected to different ground electrodes formed on a package. The surface acoustic wave filter device according to claim 6, wherein the surface acoustic wave filter device is electrically connected. 8. An electrode connected to a ground potential of at least one of the parallel arm resonators is connected to the ground electrode provided on the package by a plurality of bonding wires, and at least one of the plurality of bonding wires is provided. The bonding wire of the present invention is connected to a ground electrode near the input side of the plurality of ground electrodes of the package, and the other bonding wire is connected to a ground electrode near the output side. The surface acoustic wave filter device according to 6 or 7. 9. The surface acoustic wave filter according to claim 1, further comprising a plurality of electrode pads for connecting to the outside, a bump made of a conductive material formed on the electrode pad, A package having a plurality of electrodes to which the surface acoustic wave filter is connected, and a package for hermetically sealing the surface acoustic wave filter, wherein the surface acoustic wave filter has the bump formed on the electrode formed on the package. A surface acoustic wave filter device characterized by being electrically connected by joining.