JP3438724B2 - Surface acoustic wave filter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a band-pass type SAW filter formed by using a plurality of surface acoustic wave (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 a bandpass filter.
A SAW filter in which a ladder type circuit is configured by using a W resonator is known (for example, Japanese Patent Laid-Open No. 56-1976).
No. 5, JP-A-5-183380). In this type of SAW filter, it is strongly required to increase the amount of attenuation in the stop band near the pass band. In recent years, for example,
In communication devices such as mobile phones, the interval between the transmission frequency and the reception frequency has become very narrow in order to improve the efficiency of radio wave utilization. Therefore, in order to increase the selectivity, it is desired to introduce a bandpass filter having steeper filter characteristics between the passband and the stopband.

Japanese Unexamined Patent Publication No. 9-55640 discloses a SAW filter that satisfies the above demands. The SAW filter described in this prior art will be described with reference to FIG.

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

The SAW filter 101 is connected to the input terminal IN and the output terminal OUT. A series arm is formed between the input terminal IN and the output terminal OUT, and the series arm has
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 configured, that is, the SAW resonators 103, 105 and 107 are respectively connected between the series arm and the reference potential to configure a parallel arm resonator.

Further, the anti-resonance frequency of the parallel arm resonators, that is, the SAW resonators 103, 105, 107 is configured to match the resonance frequency of the series arm resonators, that is, the SAW resonators 104, 106.

In the SAW filter 101, the IDTs in the SAW resonators 104 and 106 as the series arm resonators are used.
SAW resonators 103, 105, which are parallel arm resonators, are provided for the gap between the reflectors 104b, 104c and the reflectors 104b, 104c or the reflectors 106b, 106c.
A considerable gap at 107 is made larger or smaller. Therefore, spurious that occurs between the resonance frequency and the anti-resonance frequency in the parallel arm resonator is generated between the resonance frequency of the parallel arm resonators 103, 105, 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 amount near the pass band in the stop band on the low frequency side or the high frequency side of the pass band is significantly improved.

That is, by setting the distance between the IDT of the parallel arm resonator and the reflector so that the spurious component is generated in the parallel arm resonator, the filter in the frequency range from the pass band to the stop band is set. The steepness of the characteristics is enhanced, and it is possible to provide a bandpass filter with excellent selectivity.

[0009]

As described above, in the SAW filter disclosed in Japanese Patent 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 characteristic in the vicinity of the pass band can be made steep.

However, in the prior art disclosed in Japanese Unexamined Patent Publication No. 9-55640, it is necessary to adjust the gap between the IDT and the reflector, so that the manufacturing process is complicated to change when the filter characteristics are changed. It was In the case of a high frequency filter, the electrode spacing becomes very narrow, and there are many cases where electrode short-circuiting or the like occurs frequently, making manufacture difficult.

In recent years, it has been strongly desired to introduce a SAW filter having a higher degree of selectivity. Therefore, various techniques for sharpening the filter characteristic in the frequency region from the pass band to the stop band are strongly demanded. ing.

Therefore, an object of the present invention is to make the attenuation characteristic steep at the boundary between the pass band and the stop band without increasing the number of stages in a SAW filter having a ladder type circuit configuration using a SAW resonator. It is to provide a SAW filter that can be manufactured and is easy to manufacture.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, in which a series arm is provided between the input and the output, and at least 1 is provided between the series arm and the reference potential.
S having a ladder-type circuit configuration in which two parallel arms are configured
The present invention 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 1 having an IDT on the serial arm
Series arm resonator consisting of port SAW resonator is, in the parallel arm, IDT and the parallel arm resonators consisting of 1-port SAW resonator which chromatic and reflectors provided on both sides of the IDT is disposed In the surface acoustic wave filter, the anti-resonance frequency of at least one of the parallel arm resonators is set to fall within the stop band of the reflector, and spurious generated by the parallel arm resonator is
It is set to be outside the stop band of the reflector, and the spurious is the same as that of the parallel arm resonator.
Between the vibration frequency and the pass band of the surface acoustic wave filter
Of the electrode fingers of the reflector.
The period is greater than that of the interdigital transducer
The position where the spurious appears is small
The surface acoustic wave filter is characterized in that it is on the lower frequency side of the stop band frequency of the reflector .

According to a second aspect of the invention, the input and output are connected in series.
It composes an arm, and there is a small amount between the series arm and the reference potential.
A ladder type circuit configuration with at least one parallel arm
Having an interdigital transducer in the series arm
From at least one 1-port SAW resonator having
The series arm resonator that consists of
The transducer and the interdigital transducer
1-port S with reflectors on both sides of the laser
Elasticity in which parallel arm resonators composed of AW resonators are arranged
In a surface wave filter, at least one of the parallel arms
The anti-resonance frequency of the resonator is the stop band of the reflector.
It is set to enter inside, and the parallel arm resonator
The spurious generated by the
The elastic surface is
Of the wave filter and the anti-resonance circumference of the series arm resonator
Spurious of the parallel arm resonator is generated between the wave number and
And the circumference of the electrode fingers of the reflector.
Electrode finger in interdigital transducer
Is greater than the period of the
It should be designed so that it appears higher than the stop band of the reflector.
It has been made and said Rukoto.

[0016]

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

In the invention according to claim 4 , at least 2
It has a plurality of parallel arm resonators, and is configured so that spurious generated by at least one parallel arm resonator appears on the higher band side than the pass band of the surface acoustic wave filter. The spacing between the IDT and the reflector is selected so that the spurious of the resonator appears on the lower side of the pass band.

According to a fifth aspect of the present invention, there is provided the surface acoustic wave filter according to any one of the first to fourth aspects, and a package in which the surface acoustic wave filter is housed and which is hermetically sealed. A surface acoustic wave filter, characterized in that at least one electrode connected to the ground potential in the parallel arm resonator is electrically connected to a ground electrode provided in the package by a plurality of bonding wires. It is a device.

In a surface acoustic wave filter device according to a fifth aspect of the present invention, preferably, as described in the sixth aspect, a plurality of electrodes are connected to the ground potential in at least one of the parallel arm resonators. Bonding wires are connected, and the plurality of bonding wires are electrically connected to different ground electrodes formed on the package.

According to a seventh aspect of the present invention, at least one electrode connected to the ground potential in the parallel arm resonator is connected to the ground electrode provided in the package by a plurality of bonding wires, and a plurality of electrodes are connected. At least one of the bonding wires of the above 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. Is characterized by.

The invention according to claim 8 further comprises a plurality of electrode pads for connection to the outside, and the surface acoustic wave filter according to any one of claims 1 to 7 , and electrodes of the surface acoustic wave filter. The surface acoustic wave filter includes a bump formed of a conductive material on the pad, a plurality of electrodes to which the surface acoustic wave filter is connected, and a package for hermetically sealing the surface acoustic wave filter. In the surface acoustic wave filter device, the bumps are electrically connected by being joined to the electrodes formed on the package.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be clarified by giving 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 the first reference example. The SAW filter 1 is configured using a rectangular surface wave substrate 2. The surface wave substrate 2 is 36 ° in this embodiment.
It is composed of a rotation Y-cut LiTaO ₃ piezoelectric substrate. However, the surface 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 made of a 1-port type SAW resonator, and similarly, series arm resonators 4 made of a 1-port type SAW resonator, respectively. 6 and 6 are configured. Each SAW resonator 3 ~
7 has IDTs 3a to 7a in the center, and each has an IDT
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 the input terminal IN and the 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 in the series arm. On the other hand, three parallel arms are formed between the series arm and the reference potential. That is, the parallel arm resonators 3, 5, and 7 described above are respectively connected between the series arm and the reference potential.

It should be noted that one of the comb-teeth electrodes of the IDT 3a of the SAW resonator 3 is connected to the ID of the SAW resonator 4 by the connection electrode 8.
It is connected to one comb tooth electrode of T4a. Further, the connection electrode 9 uses the other comb-teeth electrode of the IDT 4a as the IDT 4a.
5a is connected to one of the comb electrodes and one of the IDTs 6a is connected to the comb electrode. The connection electrode 10 is an IDT.
The other comb-shaped electrode 6a is electrically connected to one comb-shaped electrode 7a of the IDT 7a.

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

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

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

The feature of this reference example is that the parallel arm resonators 3, 5,
The width of the outermost electrode finger of the IDT 7 is smaller than the widths of the other electrode fingers of the IDT. This will be described with reference to FIG. 2 as a representative of the parallel arm resonator 3.

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

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 the 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, in the center IDTs 5a and 7a, the widths of the electrode fingers on both sides in the surface propagation direction are different. , Is smaller than the width of other electrode fingers in the IDT.

It will be described that the filter characteristics from the pass band to the stop band can be made steep by making the widths of the electrode fingers in the IDT different as described above. SAW
The spurious component of the resonator is generated by the 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 microfabrication process such as photolithography. Therefore, both the IDT and the reflector have a similar structure and reflect the surface wave.

Therefore, when an electrode finger having a partially different electrode finger width exists in the IDT, the phase disturbance occurs due to the reflection of the surface wave at the electrode finger, and spurious is generated.
As in this reference example, the outermost electrode fingers 3a ₁ of the IDT 3,
When the width of 3a ₂ is made smaller than the width of the other electrode fingers 3a ₃ of the IDT ₃ , the phase change of the reflected wave becomes small,
The same effect as when the gap between 3a and the reflectors 3b and 3c is narrowed can be obtained. That is, spurious appears on the lower frequency side than the resonance frequency of the parallel arm resonator. Further, the frequency position of this 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 low pass band side can be enhanced.

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

(Second Reference Example) SA according to the second reference example
The W filter is the same as the first reference example except that the structure of the electrode fingers 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 the electrode structure shown in FIG. Figure 3
As shown in FIG. 5, 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.
Has been made wider than. The busbar 3d has a structure in which the busbar of the IDT 3a and the busbars of the reflectors 3b and 3c are commonly used.
The busbars of the reflectors 3b and 3c may be separated.

Also in the other parallel arm resonators 5 and 7, the central IDTs 5a and 7a are constructed in the same manner as the IDT 3a of the parallel arm resonator 3 described above. 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.

In the parallel arm resonator 3 as in this reference example,
Outermost electrode finger 3a of the IDT 3a _Four, 3a_FiveWidth of I
Remaining electrode fingers 3a of DT3a₃If it is larger than the width of
The phase change of the reflected wave becomes large, and the IDT 3a and the reflector 3
The same effect as when the interval between b and 3c is widened is obtained.
It That is, it is higher than the anti-resonance frequency of the series arm resonator.
Spurious occurs on the side. This spurious occurs
The frequency position is the outermost electrode finger 3 of the IDT 3a.
a_Four, 3a_FiveThe width can be adjusted arbitrarily.

Therefore, the series arm resonators 4 and 6 (see FIG. 1)
Of the parallel arm resonators 3, so that the above spurious is generated between the anti-resonance frequency of 1 and the pass band of the SAW filter 1.
By making the width of the outermost electrode fingers of the IDTs 5a, 5a, and 7a of 5 and 7 larger than the widths of the remaining electrode fingers of the IDTs, the steepness of the filter characteristics on the high pass band side can be improved. it can. Also in the SAW filter of the present reference example, for example, only by changing the width of the electrode fingers in the IDT, the steepness of the filter characteristics on the high frequency side of the pass band can be increased, so that the electrode interval can be made constant, It is possible to suppress variations in manufacturing and short-circuit defects of the electrodes, and it is possible to simplify the manufacturing process as compared with the SAW filter described in Japanese Patent Laid-Open No. 9-55640.

(Third Reference Example) The first and second reference examples are
The widths of the electrode fingers of the IDTs in the parallel arm resonators 3, 5, and 7 are made different so as to make the filter characteristics steep from the pass band to the stop band, but it is also possible to make the widths of the electrode fingers in the reflector different. Similarly, it is possible to make the filter characteristic steep from the pass band to the stop band.

The SAW filter according to the third reference example is intended to make the filter characteristic steep from the pass band to the stop band by making the width of the electrode finger of the reflector in the parallel arm resonator different.

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

As shown in FIG. 4, in the parallel arm resonator 3, the grating reflectors 3b and 3b are provided on both sides of the IDT 3a.
3c is arranged, but among the plurality of electrode fingers of each reflector 3b, 3c, the electrode finger 3b closest to the IDT 3a.
The widths of ₁ and 3c ₁ are the electrode fingers 3b of the remaining reflectors 3b and 3c.
_It is made larger than ₂ , 3c ₂ .

Since the IDT 3a and the reflectors 3b and 3c have similar structures as described above, they reflect surface acoustic waves. Therefore, if there are electrode fingers with partially different electrode finger widths in the reflector, the reflection at the electrode fingers causes phase disturbance and spurious is generated.

Of the plurality of electrode fingers of the reflectors 3b and 3c, the electrode fingers 3b ₁ and 3b on the side closest to the IDT 3a.
When the width of c ₁ is made larger than the widths of the remaining electrode fingers, the phase change of the reflected wave becomes large, and the same effect as when the distance between the electrode fingers in the IDT is widened is obtained. That is, due to the parallel arm resonator 3, spurious is generated on the higher frequency side than the anti-resonance frequency of the series arm resonator, and the frequency position of this spurious can be arbitrarily adjusted by the width of the electrode fingers 3b ₁ and 3c _1. You can

Therefore, by setting so that the above spurious appears between the anti-resonance frequency of the series arm resonators 4 and 6 (see FIG. 1) constituting the ladder type filter and the pass band of the filter, It is possible to enhance the steepness of the filter characteristic on the high band side of the pass band.

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

Also in this reference example, since it is not necessary to adjust the gap between the IDT and the reflector, the method disclosed in JP-A-9-5 is used.
The manufacturing process can be facilitated as compared with the method disclosed in Japanese Patent No. 5640.

In this reference example, the width of the electrode fingers 3b ₁ and 3c ₁ of the reflectors 3b and 3c closest to the IDT 3a is set to
Although it is made larger than the remaining electrode fingers 3b ₂ and 3c _{2 of the} reflector, it may be made smaller to improve steepness of the filter characteristic on the low frequency 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 incorporated.

The structure of the parallel arm resonator in the SAW filter according to the first embodiment will be described with reference to FIG. 5 on behalf of the parallel arm resonator 3. 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. 5, the IDT3
The electrode finger pitch λ of the plurality of electrode fingers 3a _{3 in} a
_{The IDT} has the electrode fingers 3b ₂ and 3c _{2 on} the reflectors 3b and 3c.
The pitch λ _REF is 1.02 times. With this structure, the spurious due to the reflection of the surface acoustic wave is made lower than the stop band of the parallel arm resonator, so that the filter characteristic on the low 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, due to the reflection of surface acoustic waves
Generate spurious near the pass band and
When increasing the steepness of the filter characteristics, the spurious generated
The main resonance used and spurious compound in
Parallel resonance due to pedestal occurs. 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
In other words, that is, described in JP-A-9-55640
When a parallel arm resonator is constructed according to the method of FIG.
As indicated by the arrow A in (a),
Impedance rises and the impedance peak
Ku A appears. Conversely, if the gap is 0.5λ _RefThan
When it is increased, as shown by arrow B in FIG.
In addition, the impedance peak B is present on the high side of the spurious.
Be done.

As described above, when the impedance rises on the low frequency side or high frequency side of the spurious and high impedance peaks A and B appear, when the SAW filter 1 having the ladder type circuit configuration is configured, it is within the stop band. A spike-shaped ripple appears on the line, which causes deterioration of the attenuation. In particular, when the Q value of spurious resonance is high, the influence of the high impedance peaks A and B becomes large, 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 the spurious resonance. Therefore, the Q value can be lowered by adding a resistance component to the parallel arm resonator to increase the loss.
However, in that case, the Q value of the main resonance also becomes low, which deteriorates the filter characteristics. Particularly, 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 the decrease of 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 the present 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 inter-electrode finger pitch in the IDT 3a as compared with the inter-electrode finger pitch of the reflectors 3b and 3c, the Q value is lowered near the spurious resonance and the Q value is increased near the resonance frequency of the main resonance. It is possible to raise.

The cavity type 1-port SAW resonator is essentially composed of reflectors provided on both sides of the IDT.
By confining the surface wave energy in the resonator,
It has a high Q value. The reflectivity of the reflector is close to total internal reflection within a finite frequency range called the 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 so that the anti-resonance frequency of the main resonance is located inside the stop band and the spurious resonance is located outside the stop band, the above-mentioned high impedance of spurious can be achieved without deteriorating the insertion loss. The peak 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 band width of the stop band is determined by the reflectance and the width of the electrode finger of the reflector. Further, the resonance frequency and the anti-resonance 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 anti-resonance frequency can be set at an arbitrary position with respect to the stop band.

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

On the contrary, in FIG. 8B, as in the second embodiment shown in FIG. 6, the electrode finger pitch λ _IDT of the _IDT 3a is made narrower than the electrode finger pitch λ _Ref of the reflectors 3b and 3c. The impedance-frequency characteristic in the case is shown. Even in this case, the frequency of the resonator moves to the higher side of the 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 characteristic in the vicinity of the spurious generated by the parallel arm resonator. FIG. 9 shows the IDT 3a and the reflectors 3b and 3
The characteristics when spurious is generated between the resonance frequency and the anti-resonance frequency by reducing the gap with c are shown. 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, which is 1.02, and
The distance from DT, that is, 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 characteristics when the different finger widths are set are as follows. The alternate long and short dash line E indicates that the electrode finger pitch ratio is 1.
00, gap = 0.50λ _IDT , so that IDT
The characteristics in the case of setting different electrode finger widths in FIG.

As is clear from FIG. 9, the solid line C and the broken line D are different from the characteristic of the one-dot chain line E which does not generate spurious.
It can be seen from the impedance characteristics shown in (1) that the impedance change of the resonator from the anti-resonance frequency to the resonance frequency is large. Further, comparing the impedance change when the pitch ratio is 1.02 (solid line C) and when the pitch ratio is 1.0 (broken line D), it is found that there is almost no difference in the steepness of the impedance change.

On the other hand, with respect to the high impedance peak of spurious, it can be seen that the characteristic indicated by the solid line C with the electrode finger pitch ratio of 1.02 is smaller than the characteristic indicated by the broken line D. Therefore, as indicated by the solid line C, by making the electrode finger pitch ratio larger than 1 and making the gap smaller than 0.5λ, it is possible to suppress deterioration of attenuation due to spurious while maintaining high steepness. I understand.

FIG. 10 is a diagram showing impedance characteristics of the resonator when the above spurious is generated on the higher frequency side than the anti-resonance frequency. When the steepness is required on the high frequency side of the anti-resonance frequency, the spurious component appears on the high 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 DT and the reflector is set to 0.5λ or more and the upper limit of the stop band is located between the antiresonance frequency and the spurious frequency.

A solid line F in FIG. 10 is the electrode finger pitch ratio = 0.98, a gap = 0.60λ _IDT , and a broken line G.
Is the electrode finger pitch ratio = 1.00, gap = 0.65λ
_IDT and alternate long and short dash line H show respective characteristics in the case of electrode ratio pitch ratio = 1.00 and cap = 0.50λ _IDT .

As is apparent from FIG. 10, also in this case, the alternate long and short dash line H in the case of the gap = 0.50λ _IDT
Compared with the characteristics shown by, the solid line F in which the gap is enlarged by making the electrode finger width different in the IDT to generate spurious
It can be seen from the impedance characteristics shown by the broken line G and the steepness of the impedance change from the anti-resonance frequency to the high frequency side.

Further, by comparing the solid line F with the broken line G, it can be seen that the characteristics of the solid line F with the electrode finger pitch ratio of 0.98 can reduce the high impedance peak in the spurious.

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

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

FIG. 12 shows an electrode finger pitch ratio of 0.9 in the parallel arm resonator 3 shown in FIG. 6 in the second embodiment.
FIG. 8 is a diagram showing frequency characteristics of the SAW filter 1 when set to 8. The electrode finger pitch ratio is 0.98 also in the other parallel arm resonators 5 and 7.

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 due to the high impedance peak occurs in the attenuation region on the higher side of the pass band, but in the present embodiment, the pitch ratio is 0.98. It can be seen that by decreasing the value, the high impedance peak can be suppressed and the attenuation amount can be improved by about 3 dB.

Therefore, as is apparent from the first and second embodiments described above, by adjusting the electrode finger pitch ratio between the IDT and the reflector in the parallel arm resonator, high steepness is obtained in the vicinity of the pass band. 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 wave substrate 22. That is, the three parallel arm resonators 23, 25, 27
And two series arm resonators 24 and 26. That is, the 1-port SAW resonators 24 and 26 are connected as series arm resonators between the input terminal IN and the output terminal OUT.
Has been inserted. In addition, the parallel arm resonators 23, 25, 27
Are each connected between the series arm and ground potential. Note that reference numerals 28 to 30 denote connection electrodes, respectively, and form a ladder circuit having the parallel arm resonators 23, 25, 27 and the series arm resonators 24, 26.

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

Regarding the other points, the SA shown in FIG.
It is configured similarly to the W filter 1. In the ladder type filter, when a plurality of parallel arm resonators are used, each parallel arm resonator can be individually designed. Therefore, the spurious that is introduced in order to make the filter characteristics steep as described above can also be provided at different frequency positions in each parallel arm resonator. Therefore, by slightly shifting the frequency position of the spurious in the plurality of parallel arm resonators, although the steepness of the filter characteristic is slightly deteriorated, it is possible to effectively suppress the high impedance peak due to the spurious mentioned above, Good damping characteristics can be obtained. Further, by making the spurious frequencies different between the parallel arm resonators, it is possible to suppress a decrease in yield due to variations in manufacturing.

In particular, when it is necessary to increase the amount of attenuation near the pass band on both the high band side and the low band side of the pass band, the configuration of this embodiment can be preferably used. That is, the electrode finger widths in the IDT are made different so that the above-mentioned gap of the parallel arm resonators 23 and 27 becomes smaller than 0.5λ _IDT like 0.42λ _IDT , and thus the above-mentioned gap is placed on the lower side of the pass band. To generate spurious to increase steepness, while increasing the gap of the parallel arm resonator 25 above 0.5λ _IDT such as 0.56λ _IDT to increase steepness in the high band side of the pass band. By generating the spurious noise, the steepness of the filter characteristic 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, the conventional SA is shown in FIG.
The attenuation frequency characteristic of a W filter is shown. The characteristics shown in FIG. 15 are characteristics in the case where the gaps, the electrode finger widths, and the pitches of all the parallel arm resonators are equal, and the gap is 0.5λ _IDT . As is clear from the comparison between FIG. 14 and FIG. 15, the SAW filter of the present embodiment can improve the attenuation amount in the vicinity of the pass band by about 10 dB.

(Fourth Embodiment) The fourth embodiment is an embodiment of 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, first, a conventional surface acoustic wave filter device will be described with reference to FIG. The surface acoustic wave filter device 31 has a structure in which the 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. Electrodes 33a to 33c, 3 are provided on the step portion 32b, respectively.
4a to 34c are formed. Electrodes 33a-33c,
34a to 34c are drawn out of the package 32 and are configured to be electrically connected to the outside.

Parallel arm resonator 10 of SAW filter 101
One of the IDTs 103a of the third IDT 103a, that is, the comb-tooth electrode connected to the ground potential, is connected to the electrode 33a by the bonding wire 35a. Electrode 33a
Is an electrode connected to ground potential.

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

Further, the connection electrode 110 is connected to the electrode 34b by the bonding wire 35d. On the other hand, one comb tooth 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.

On the other hand, FIG. 17 is a plan view for explaining the SAW filter device according to the 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 the package 42. The package 42 is the package 3 described above.
It is constructed in the same manner as 2. That is, on both sides of the bottom surface 42a, stepped portions 42b, 42c higher in height than the bottom surface 42a are provided.
Are formed, and the electrodes 43a to 43c are formed on the step 42b.
The electrodes 44a to 44c are respectively formed on the stepped portion 42c.

ID of the parallel arm resonator 3 of the SAW filter 1
The comb-teeth electrode on the side connected to the ground potential of T is connected to the electrodes 43a, 43 by the bonding wires 45a, 45b.
connected to c. That is, the comb-teeth 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 the electrode 43b as an input electrode by the bonding wire 45c. The comb-teeth electrode on the side of the parallel arm resonator 5 connected to the ground potential of the IDT is the bonding wire 45.
d and 45e respectively connect to different electrodes 44a and 44c which are connected to the ground potential. That is, with the two bonding wires 45d and 45e,
It is connected to different electrodes 44a and 44c formed on the package 42 side and connected to the ground potential.

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

As described above, in the parallel arm resonator, when the above-mentioned spurious is used to make the filter characteristic steep from the pass band to the stop band, the high impedance peak due to the spurious has an attenuation amount near the spurious frequency. It appears remarkably when it is small, and is suppressed as the amount of attenuation increases. The amount of attenuation on the low frequency side of the pass band is maximum near the resonance frequency of the parallel arm resonator, and rapidly decreases with distance from the resonance frequency.

Therefore, by bringing the spurious frequency and the resonance frequency of the parallel arm resonator close to each other, the high impedance peak due to the spurious can be suppressed.
However, when the spurious frequency is lowered to bring the spurious frequency and the resonance frequency of the parallel arm resonator close to each other, the trap due to the spurious shifts the shoulder of the pass band, and the effect of sharpening the filter characteristic cannot 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 the 1-port SAW resonator is lowered by inserting an inductance in series with the 1-port SAW resonator.
Further, in the SAW filter device, a bonding wire made of Al, Au, or the like is normally used for electrical connection with the package, but the wiring bonding wire inevitably adds inductance.

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

SAW according to the fourth embodiment shown in FIG.
The filter device 41 is characterized in that the inductance component is reduced by devising a bonding wire connection structure. This is shown in FIGS.
Will be described with reference to.

FIG. 19 is a circuit diagram showing an equivalent circuit including the inductance component of the conventional SAW filter device shown in FIG. Here, since the parallel arm resonator is connected in series with 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, the inductance La added to the resonator is as follows. It is represented by a formula.

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

Here, in the parallel arm resonators 3 and 5,
Since the two bonding wires 45a, 45b and 45d, 45e are electrically connected to the ground potential, the inductance L1 of the bonding wire and the residual inductance L2 of the package are inserted in parallel. It 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 by comparing the equations (1) and (2), the inductance component is reduced in the embodiment shown in FIG. can do.

22 shows the frequency characteristic of the conventional SAW filter device shown in FIG. 16, and FIG. 23 shows the frequency characteristic of the SAW filter device 41 according to the fourth embodiment shown in FIG. . As is apparent from FIG. 22, in the conventional SAW filter device 31, although the steepness from the pass band to the stop band is enhanced due to the generation of spurious components, the attenuation amount is 16 dB due to the influence of the high impedance peak point due to the spurious components. Stays in.

On the other hand, as is apparent from FIG. 23, in the SAW filter device according to the fourth embodiment, the trap frequency due to the main resonance on the low frequency side becomes high, so that the spurious level becomes small as a whole. It can be seen that the attenuation amount 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 this SAW filter device 51, the SAW filter 1 is fixed to the bottom surface 42 a of the package 42. The comb-teeth electrodes connected to the ground potential of the IDT of the parallel arm resonator 3 are connected to the electrodes 43a and 44a formed on the package 42 side and connected to the ground potential by the bonding wires 55a and 55b. Further, the comb-teeth electrode connected to the ground potential of the IDT of the parallel arm resonator 5 is connected to the ground potential formed on the package 42 by the bonding wires 55c and 55d.
3c and 44a, respectively. Further, the comb-teeth electrode connected to the ground potential of the IDT of the parallel arm resonator 7 is connected to the ground potential formed on the package 42 by the bonding wires 55e and 55f.
3c and 44c, respectively. Other configurations are similar to those of the SAW filter device 41.

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

FIG. 21 shows an equivalent circuit including the inductance component of the SAW filter device 51. In the SAW filter device 21, the wiring of the bonding wire reduces the inductance of the parallel arm resonator. That is, by using the two bonding wires as described above for the comb-teeth electrode connected to the ground potential of the IDT of the parallel arm resonator, and connecting the two bonding wires to different ground potentials on the package side. , L1 + L2 + L3 inductances are inserted in parallel to the respective parallel arm resonators. Therefore, the inductance Lc applied to the parallel arm resonator is Lc = (L1 + L2 + L
3) / 2 will be represented. Therefore, the inductance can be halved as compared with the conventional SAW filter device 31 shown in FIG.

FIG. 24 shows the attenuation frequency characteristic of the SAW filter device 51 shown in FIG. As is apparent from FIG. 24, as compared with the frequency characteristics of the fourth embodiment shown in FIG. 23, the trap frequency due to the main resonance on the low frequency side is further increased, and the spurious level on the low frequency side of the pass band is the whole. 2 becomes smaller, and the amount of attenuation in the element band is
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. 6 is a cross-sectional view for explaining the SAW filter device according to the example of FIG.

In the SAW filter device 61, the package is composed of 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. The SAW filter 1 is fixed to the package substrate 62 by a mounting method called a face-down method. That is, the bumps 65a and 65b made of solder or the like are formed on the electrode pads 1a and 1b for connecting to the outside of the SAW filter 1, and the SAWs are oriented so that the bumps 65a and 65b face downward.
The SAW filter 1 is electrically connected to the package substrate 62 by disposing the filter 1 and joining the bumps 65 a and 65 b to the electrodes 66 a and 66 b formed on the package substrate 62. In addition, the electrode pads 1a and 1b
Indicates an electrode portion connected to the outside of the SAW filter device 1, and corresponds to, for example, the comb-teeth electrode connected to the ground potential of the parallel arm resonator or the connection electrodes 8 to 10 described above. Note that in FIG. 25, the SA according to the first reference example is used.
Although the W filter 1 is shown as a representative example, the SAW filter according to another embodiment of the present invention can be fixed to the package substrate 62 by the face-down method in the same manner.

In the SAW filter 61 of the present invention, the package and the S via the bumps 65a and 65b are formed by the face down method without using bonding wires.
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, and thereby 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 characteristics in the frequency region from the pass band to the stop band due to spurious, and to further increase the attenuation amount 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, and the filter is used. Since the spurious that is generated to enhance the steepness of the characteristics is set to be outside the stop band of the parallel arm resonator, the spurious above for increasing the steepness of the filter characteristics without deteriorating the insertion loss. It is possible to suppress the high impedance peak due to the above, and it is possible to secure a sufficient amount of attenuation in the stop band.

Further , the spurious is configured to be generated between the resonance frequency of the parallel arm resonator and the pass band of the SAW filter, and the period of the electrode fingers of the reflector is ID.
Since it is smaller than the period of T, and the frequency position where the spurious appears is lower than the stop band frequency of the parallel arm resonator, it is caused by the spurious for achieving steep filter characteristics. It is possible to reliably suppress the high impedance peak that occurs and to secure a sufficient amount of attenuation in the stop band.

In the invention described in claim 2 , SAW
The spurious 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. Since the spurious is configured to appear on the higher band side than the stop band of the parallel arm resonator, it is possible to make the filter characteristic steep on the higher band side of the pass band, and A sufficient amount of attenuation can be secured in the stop band on the higher side of the pass band.

According to the third aspect of the invention, at least two or more parallel arm resonators in which spurious components for generating the steep filter characteristic are generated are arranged in the parallel arm, and at least one parallel arm resonator is provided. Since the spurious generated by the arm resonator is configured to appear in a different frequency range from the spurious generated by other parallel arm resonators, it is possible to suppress the high impedance peak due to the spurious generation. In addition, it is possible to suppress a decrease in yield due to variations in manufacturing.

According to the invention described in claim 4 , there is at least two parallel arm resonators, and the spurious generated by the at least one parallel arm resonator is higher than the pass band of the SAW filter. Is configured to appear on the side, and spurious generated by other parallel arm resonators
Since the interval between the IDT and the reflector is selected so as to appear on the low frequency side of the pass band, the spurious noise appears on both the low frequency side and high frequency side of the pass band, and the filter is applied in both of these areas. The steepness of the characteristics can be improved.

According to the invention described in claim 5 , 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. Since it is electrically connected to the ground electrode provided in the, it is possible to reduce the inductance added in series to the parallel arm resonator, and it is possible to suppress the high impedance peak due to the above spurious emission. The amount of attenuation in the stop band can be improved.

According to the invention described in claim 6 , 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, it is possible to further reduce the inductance applied in series to the parallel arm resonator, and thereby the filter near the pass band. Not only can the steepness of the characteristics be enhanced, but also the high impedance peak associated with the spurious can be suppressed more effectively, and the amount of attenuation in the stop band can be further increased.

According to the invention described in claim 7 , the electrode connected to the ground potential in at least one parallel arm resonator is connected to the ground electrode provided in the package by a plurality of bonding wires. At least one bonding wire 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. It can be reduced to about 1/2 of that of the conventional one, and the amount of attenuation in the stop band can be further increased.

In the SAW filter device according to the eighth aspect of the present invention, the SAW filter, the bumps made of a conductive material formed on the electrode pads of the SAW filter, and the S
It has a plurality of electrodes to which the AW filter is connected, and SA
And a package for hermetically sealing the W filter,
The SAW filter is electrically connected to the electrodes of the package by joining the bumps to the electrodes formed on the package, that is, the SAW filter is electrically connected to the electrodes of the package in a face-down manner. So you don't need bonding wires. Therefore, the inductance added to the parallel arm resonator can be made extremely small, and the attenuation amount in the stop band on the lower side of the pass band can be further improved.

[Brief description of drawings]

FIG. 1 is a schematic plan view for explaining 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 the 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 the second embodiment.

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

8A and 8B are diagrams for explaining the impedance characteristic and the stop band of the conventional 1-port SAW resonator and the parallel arm resonator according to the second embodiment, respectively.

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

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

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

FIG. 12 is a diagram showing frequency characteristics of the SAW filter according to the 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 showing 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 for explaining 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.

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

23 is a diagram showing frequency characteristics of the SAW filter device of the embodiment shown in FIG.

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

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]

1 ... SAW filter 1a, 1b ... Electrode pad 2 ... Surface wave substrate 3, 5, 7 ... Parallel arm resonator 3a, 5a, 7a ... IDT 3b, 3c, 5a, 5b, 5c, 7a, 7c ... Reflector 4, 6 ... Series arm resonators 4a, 6a ... IDT 21 ... SAW filter 22 ... Surface wave substrate 23, 25, 29 ... Parallel arm resonators 23a, 25a, 27a ... IDT 23b, 23c, 25b, 25c, 27b, 27c ... Reflection 24, 26 ... Series arm resonators 24a, 26a ... IDT 41 ... SAW filter device 42 ... Packages 43a-43c, 44a-44c ... Package electrodes 45a-45g ... Bonding wires 51 ... SAW filter devices 55a-55f ... Bonding wires 61 ... SAW filter device 62 ... Package substrate 63 ... Caps 65a, 65b ... Bumps 66a, 66b ... Electrodes formed on the cage

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-8-181561 (JP, A) JP-A-9-55640 (JP, A) JP-A-10-209806 (JP, A) JP-A-9- 246913 (JP, A) JP-A-6-338756 (JP, A) JP-A-60-213110 (JP, A) Actual Kaihei 6-9231 (JP, U) International Publication 96/015587 (WO, A1) M ． Ueda, O .; Kawachi, K .; Hashimoto, O .; Ikat a, and Y. Satoh, Low Loss Ladder Type S AW Filter in The R ange of 300 to 400MHz, Proceedings of 1994 ULTRASONICS SYM POSIUM, November 4, 1994, Vol. 1, p. 143-146 (58) Fields investigated (Int.Cl. ⁷ , DB name) H03H 9/25 H03H 9/64

Claims (8)

(57) [Claims] 1. 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 the series arm has an interlaced arm structure. series arm resonator consisting of at least one one-port SAW resonator having a digital transducer, the parallel arm, and interdigital transducers, one-port for chromatic and reflectors provided on both sides of the interdigital transducer In a surface acoustic wave filter in which a parallel arm resonator composed of a SAW resonator is arranged, at least one anti-resonance frequency of the parallel arm resonator is
It is set to be in the stop band of the reflector, and spurious generated by the parallel arm resonator is set to be outside the stop band of the reflector, and the spurious is, Parallel arm resonator
Between the resonance frequency of and the pass band of the surface acoustic wave filter
An electrode of the reflector that is configured to
The finger cycle is the interdigital transducer cycle.
The position where the spurious appears is the stop of the reflector.
A surface acoustic wave filter characterized by being located at a lower frequency side than a band frequency . 2. A serial arm is formed between the input and the output, and
There is at least one parallel arm between the series arm and the reference potential.
Has a ladder-type circuit configuration that is
At least one with a digital converter
The series arm resonator consisting of the 1-port SAW resonator of
On the parallel arm, an interdigital transducer and
Provided on both sides of the interdigital transducer
Parallel consisting of 1-port SAW resonator with reflector
A surface acoustic wave filter in which the arm resonator is arranged.
And the anti-resonance frequency of at least one of the parallel arm resonators is
Set to fit within the reflector stopband
And spurious generated by parallel arm resonators
Is set outside the stop band of the reflector.
In addition, it is configured such that spurious of the parallel arm resonator is generated between the pass band of the surface acoustic wave filter and the anti-resonance frequency of the series arm resonator, and the reflector. The period of the electrode fingers of the interdigital transducer is made larger than the period of the electrode fingers, the spurious is configured to appear on the high frequency side of the stop band of the reflector ,
Surface acoustic wave filter. 3. At least two parallel arm resonators in which the spurious component is generated are arranged in parallel arms, and the spurious generated by at least one parallel arm resonator is in another parallel arm resonance. characterized in that it is configured to be generated in a different frequency range from that of the spurious generated by the child, the surface acoustic wave filter according to claim 1 or 2. 4. Having at least two parallel arm resonators,
The spurious generated by at least one parallel arm resonator is configured to appear on the higher frequency side than the pass band of the surface acoustic wave filter, and the spurious of other parallel arm resonators is higher than the pass band. is configured to appear in the low-frequency side, the surface acoustic wave filter according to any one of claims 1-3. 5. A surface acoustic wave filter according to any one of claims 1-4, which is accommodated the surface acoustic wave filter, and a package that is hermetically sealed, at least one of the parallel A surface acoustic wave filter device, wherein an electrode connected to the ground potential in the arm resonator is electrically connected to a ground electrode provided on the package by a plurality of bonding wires. 6. A plurality of bonding wires are connected to an electrode connected to the ground potential of at least one of the parallel arm resonators, and the plurality of bonding wires are electrically connected to different ground electrodes formed on the package. The surface acoustic wave filter device according to claim 5 , wherein the surface acoustic wave filter device is electrically connected. 7. An electrode connected to the ground potential in 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 connected to the ground electrode. The bonding wire of the book 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 the ground electrode near the output side. 5. The surface acoustic wave filter device according to 5 or 6 . And the surface acoustic wave filter according to any one of claims 8] claim further comprising a plurality of electrode pads for connecting to external 1-7, a bump made of a conductive material formed on the electrode pads, A surface acoustic wave filter is provided with 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 includes the bumps on the electrodes formed on the package. A surface acoustic wave filter device, wherein the surface acoustic wave filter device is electrically connected by being joined.