JP4534307B2 - Surface acoustic wave filter - Google Patents

Surface acoustic wave filter Download PDF

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Publication number
JP4534307B2
JP4534307B2 JP2000152389A JP2000152389A JP4534307B2 JP 4534307 B2 JP4534307 B2 JP 4534307B2 JP 2000152389 A JP2000152389 A JP 2000152389A JP 2000152389 A JP2000152389 A JP 2000152389A JP 4534307 B2 JP4534307 B2 JP 4534307B2
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electrode
reflector
comb
electrodes
reflector electrode
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JP2001332954A (en
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成大 三田
昭雄 常川
和生 池田
関　　俊一
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Panasonic Corp
Panasonic Holdings Corp
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Panasonic Corp
Matsushita Electric Industrial Co Ltd
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Description

【０００１】
【発明の属する技術分野】
本発明は例えば、無線通信機器における高周波回路などに使用される弾性表面波フィルタに関するものである。
【０００２】
【従来の技術】
従来、ＲＦ段に適する弾性表面波フィルタとしては、縦モード結合共振器型弾性表面波フィルタがよく知られており、回路の簡素化、高性能化のため、選択的に高減衰量を確保できるものが要望されている。
【０００３】
以下、従来の縦モード結合型設計を用いた弾性表面波フィルタについて説明する。
【０００４】
図１２は従来の縦モード結合型弾性表面波フィルタの上面図である。
【０００５】
圧電基板８０上に一点鎖線で囲んだ三電極型櫛電極８１，８２を縦続接続する。三電極型櫛電極８１，８２はそれぞれ点線で囲んだ第１の櫛型電極８１ａ，８２ａ、第２の櫛型電極８１ｂ，８２ｂ、第３の櫛型電極８１ｃ，８２ｃと、それらの両側の反射器電極８１ｄ，８２ｄが表面波伝搬方向に配置されている。
【０００６】
三電極型櫛電極８１の第１の櫛型電極８１ａは、対向する両電極指の一方が出力端子８３に他方がアース端子８５に接続されている。三電極型櫛電極８２の第１の櫛型電極８２ａも、対向する両電極指の一方が出力端子８４に他方がアース端子８６に接続されている。
【０００７】
三電極型櫛電極８１，８２の第１の櫛型電極８１ａ，８２ａに電圧を印加することにより表面波が励起され、反射器電極８１ｄ，８２ｄでエネルギーが閉じ込められることによりフィルタ特性が形成される。
【０００８】
また反射器電極８１ｄ，８２ｄは電極指幅及び電極指間隔を一定にして形成したものであった。
【０００９】
【発明が解決しようとする課題】
反射器電極特性は反射効率の良い通過周波数範囲とその両側の周期的なスロープ特性で形成される。そのため上記構成においては通過帯域近傍で反射器電極の周期的な特性が波形として現われ、スプリアスが発生することになる。その結果通過周波数帯域近傍での減衰量確保が困難であるという問題点を有していた。
【００１０】
そこで本発明は、通過周波数帯域近傍の減衰量を十分に確保することのできる弾性表面波フィルタを提供することを目的とするものである。
【００１１】
【課題を解決するための手段】
この目的を達成するために本発明の弾性表面波フィルタは、圧電基板と、この圧電基板上に設けた第１の櫛型電極と、この第１の櫛型電極のその表面波伝搬方向の両側に設けた第２、第３の櫛型電極と、この第２及び第３の櫛型電極を挟むように設けた第１及び第２の反射器電極とを備え、前記反射器電極は複数本の電極指の反射器電極ピッチ（電極指幅＋電極指間隔幅）が一定となる、複数の反射器電極群に分けられ、それぞれの前記反射器電極群の間で前記反射器電極ピッチが異なり、隣り合う前記反射器電極群の反射器電極ピッチ同士は、０．０５％以上の差を有しているものであり、反射器電極の通過周波数帯域近傍の周期的なスロープ特性を乱すことにより、スプリアスを抑制し、上記目的を達成することができる。
【００１２】
【発明の実施の形態】
本発明の請求項１に記載の発明は、圧電基板と、この圧電基板上に設けた第１の櫛型電極と、この第１の櫛型電極のその表面波伝搬方向の両側に設けた第２、第３の櫛型電極と、この第２及び第３の櫛型電極を挟むように設けた第１及び第２の反射器電極とを備え、前記反射器電極は複数本の電極指の反射器電極ピッチ（電極指幅＋電極指間隔幅）が一定となる、複数の反射器電極群に分けられ、それぞれの前記反射器電極群の間で前記反射器電極ピッチが異なり、隣り合う前記反射器電極群の反射器電極ピッチ同士は、０．０５％以上の差を有している弾性表面波フィルタであり、通過周波数帯域近傍の減衰量を十分に確保することができるものである。
【００１３】
以下図面を参照しながら本発明の実施の形態について説明する。
【００１４】
（参考例１）
図１は本発明の参考例１における弾性表面波フィルタの上面図である。
【００１５】
圧電基板１０上に、第１の櫛型電極１１とその表面波伝搬方向の両側に第２、第３の櫛型電極１２，１３を配置し、それらの両側に第１の反射器電極１４と第２の反射器電極１５を備えている。第１及び第２の反射器電極１４，１５の反射器電極ピッチは、隣り合う第２及び第３の櫛型電極１２，１３から離れるにつれて徐々に小さく変化させてある。
【００１６】
この構成により、第１及び第２の反射器電極１４，１５の特性は図２のようになり、従来よりも通過帯域内近傍の低周波数側の反射効率を下げることができる。
【００１７】
また、第１及び第２の反射器電極１４，１５の反射器電極ピッチを、隣り合う第２、第３の櫛型電極１２，１３側から離れるにつれて大きく変化させると、図３に示すように通過帯域内近傍の高周波数側の反射効率を下げることができる。
【００１８】
すなわち第１、第２の反射器電極１４，１５の反射器電極ピッチを一定でなく、変えることにより反射特性を乱し、スプリアスの発生を抑制することにより、通過帯域近傍の低周波数側あるいは高周波数側の帯域外減衰量を十分に確保することができる。
【００１９】
（参考例２）
図４は本発明の参考例２における弾性表面波フィルタの上面図である。
【００２０】
圧電基板３０上に、第１の櫛型電極３１とその表面波伝搬方向の両側に第２、第３の櫛型電極３２，３３を配置し、それらの両側に第１の反射器電極３４と第２の反射器電極３５を備えている。また、第１、第２の反射器電極３４，３５は、それぞれ反射器電極ピッチが異なる。二つの反射器電極群（図４中点線で囲んでいる）３４ａ，３４ｂ，３５ａ，３５ｂで構成されている。また反射器電極群３４ａ，３５ａの反射器電極ピッチは、反射器電極群３４ｂ，３５ｂの反射器電極ピッチよりも大きくしてある。
【００２１】
図５は図４に示す第１及び第２の反射器電極３４，３５の特性図であり、第１の反射器電極３４，３５を二つの反射器電極群３４ａ，３４ｂ，３５ａ，３５ｂに分割することにより、通過帯域内近傍の低周波数側の反射効率を下げることが可能である。
【００２２】
また、反射器電極群３４ａ，３５ａの反射器電極ピッチを反射器電極群３４ｂ，３５ｂの反射器電極ピッチより小さくすると、図６に示すように通過帯域内近傍の高周波数側の反射効率を下げることが可能である。
【００２３】
すなわち第１及び第２の反射器電極３４，３５を二つ以上の反射器電極群に分割し、それぞれの反射器電極ピッチを変えてそれぞれの周期が異なるようにすることにより、反射特性の山と谷が重なり合い、この部分の反射器特性が平坦になり、スプリアスを抑制し、通過帯域近傍の低周波数側あるいは高周波数側の帯域外減衰量を十分に確保することができるのである。
【００２４】
（実施の形態１）
図７は本発明の実施の形態１における弾性表面波フィルタの上面図である。
【００２５】
圧電基板５０上に、第１の櫛型電極５１とその表面波伝搬方向の両側に第２、第３の櫛型電極５２，５３を配置し、それらの両側に第１の反射器電極５４と第２の反射器電極５５を備えた三電極縦モード結合型櫛電極５６が形成されている。また、第１の反射器電極５４及び第２の反射器電極５５は、反射器電極ピッチが異なる三つの反射器電極群５４ａ，５４ｂ，５４ｃ，５５ａ，５５ｂ，５５ｃで構成されている。反射器電極ピッチは反射器電極群５４ａ，５５ａが一番大きく、次いで反射器電極群５４ｂ，５５ｂが大きく、反射器電極群５４ｃ，５５ｃを最も小さくしている。
【００２６】
さらに、三電極縦モード結合型櫛電極５６にこれと同じ構成の三電極縦モード結合型櫛電極５７が縦続接続されている。
【００２７】
このような構成の弾性表面波フィルタにおいて、反射器電極群５４ａ，５４ｂ，５４ｃ，５５ａ，５５ｂ，５５ｃの構成を（表１）に示すような構成とした時の、第１及び第２の反射器電極５４，５５の特性を図８に示す。また図９は図８の要部拡大図である。
【００２８】
【表１】

Figure 0004534307
【００２９】
図９を見るとわかるように反射器電極群５４ａ，５５ａの反射効率が第１及び第２の反射器電極５４，５５の反射効率に対して支配的にならない範囲で、反射器電極特性を変化させることにより、通過帯域近傍の低周波数側のスプリアスを抑制し、減衰量を確保することができる。
【００３０】
つまり反射器電極群５４ａ，５５ａの電極指本数を１０本から３０本とすることが望ましいのである。第１及び第２の反射器電極５４，５５の反射効率に大きく寄与するのは第２、第３の櫛型電極５２，５３に最も近い反射器電極群５４ａ，５５ａであることを考慮すると第１及び第２の反射器電極５４，５５を構成する電極指の本数が変化したとしても、反射器電極群５４ａ，５５ａの電極指本数は１０本から３０本とすることが望ましい。
【００３１】
また、反射器電極群５４ａ，５５ａの電極指本数が３０本よりも多くなると（図９の（ｄ））、反射器電極群５４ａ，５５ａの反射効率が支配的となり、第１及び第２の反射器電極５４，５５の特性を変化させて通過帯域近傍のスプリアスを抑制することが困難となる。反対に反射器電極群５４ａ，５５ａの電極指本数が９本以下となると反射効率が不十分となり所望の特性を確保することが難しい。
【００３２】
次に反射器電極群５４ａ，５５ａの反射器電極ピッチをλａ、反射器電極群５４ｂ，５５ｂの反射器電極ピッチをλｂ、反射器電極群５４ｃ，５５ｃの反射器ピッチをλｃとし、（表２）に示すような構成とした場合の第１及び第２の反射器電極５４，５５の特性を図１０に、その要部拡大図を図１１に示す。
【００３３】
【表２】
Figure 0004534307
【００３４】
図１０を見るとわかるように、通過帯域近傍の低周波数側に減衰量を確保するには、反射器電極ピッチは第２、第３の櫛型電極５２，５３に近いほど大きく、反隣り合う反射器電極群との反射器ピッチは０．０５％以上、好ましくは０．１％以上の差を有するようにし、第２及び第３の櫛型電極５２，５３との距離が長い反射器電極群ほど反射器電極ピッチを小さくすれば良い。
【００３５】
なお、実施の形態１においては、第１及び第２の反射器電極５４，５５をそれぞれ複数の反射器電極群に分割し、第２及び第３の櫛型電極５２，５３からの距離が長い反射器電極群ほど反射器電極ピッチを小さくして通過帯域近傍の低周波数側のスプリアスを抑制し、減衰量を確保した。高周波数側の減衰量を確保したい場合は、第２及び第３の櫛型電極５２，５３からの距離が長い反射器電極群ほど反射器電極ピッチを大きくすれば良い。
【００３６】
また、三電極縦モード結合型櫛電極５６についてのみ説明したが同じ構成の三電極縦モード結合型櫛電極５７についても同様のことがいえる。
【００３７】
さらに実施の形態３においては二つの三電極縦モード結合型櫛電極５６，５７を複数縦続接続した弾性表面波フィルタについて説明したが、図１、図２に示すように一つあるいは三つ以上の三電極縦モード結合型櫛電極で構成されている弾性表面波フィルタについても、それぞれの三電極縦モード結合型櫛電極の第１及び第２の反射器電極を実施の形態１のように構成することにより同様の効果が得られるものである。
【００３８】
【発明の効果】
以上本発明によると、通過周波数帯域近傍のスプリアスを抑制し、帯域外減衰量を十分に有する弾性表面波フィルタを提供することができる。従ってこの弾性表面波フィルタを用いる携帯電話などの無線機器の高性能化及び回路の簡素化を図ることができる。
【図面の簡単な説明】
【図１】 本発明の参考例１における弾性表面波フィルタの上面図
【図２】 図１に示す弾性表面波フィルタの周波数特性曲線図
【図３】 本発明の参考例１における弾性表面波フィルタの周波数特性曲線図
【図４】 本発明の参考例２における弾性表面波フィルタの上面図
【図５】 図４に示す弾性表面波フィルタの周波数特性曲線図
【図６】 本発明の参考例２における弾性表面波フィルタの周波数特性曲線図
【図７】 本発明の実施の形態１における弾性表面波フィルタの上面図
【図８】 本発明の実施の形態１における弾性表面波フィルタの周波数特性曲線図
【図９】 図８の要部拡大図
【図１０】 本発明の実施の形態１における弾性表面波フィルタの周波数特性曲線図
【図１１】 図１０の要部拡大図
【図１２】 従来の弾性表面波フィルタの上面図
【符号の説明】
１０ 圧電基板
１１ 第１の櫛型電極
１２ 第２の櫛型電極
１３ 第３の櫛型電極
１４ 第１の反射器電極
１５ 第２の反射器電極
３０ 圧電基板
３１ 第１の櫛型電極
３２ 第２の櫛型電極
３３ 第３の櫛型電極
３４ 第１の反射器電極
３４ａ 反射器電極群
３４ｂ 反射器電極群
３５ 第２の反射器電極
３５ａ 反射器電極群
３５ｂ 反射器電極群
５０ 圧電基板
５１ 第１の櫛型電極
５２ 第２の櫛型電極
５３ 第３の櫛型電極
５４ 第１の反射器電極
５４ａ 反射器電極群
５４ｂ 反射器電極群
５４ｃ 反射器電極群
５５ 第２の反射器電極
５５ａ 反射器電極群
５５ｂ 反射器電極群
５５ｃ 反射器電極群
５６ 三電極縦モード結合型櫛電極
５７ 三電極縦モード結合型櫛電極[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave filter used for, for example, a high-frequency circuit in a wireless communication device.
[0002]
[Prior art]
Conventionally, as a surface acoustic wave filter suitable for the RF stage, a longitudinal mode coupled resonator type surface acoustic wave filter is well known, and a high attenuation can be selectively ensured in order to simplify the circuit and improve the performance. Things are desired.
[0003]
Hereinafter, a surface acoustic wave filter using a conventional longitudinal mode coupled design will be described.
[0004]
FIG. 12 is a top view of a conventional longitudinal mode coupled surface acoustic wave filter.
[0005]
Three-electrode comb electrodes 81 and 82 surrounded by an alternate long and short dash line are connected in cascade on the piezoelectric substrate 80. The three-electrode comb electrodes 81 and 82 are first comb-shaped electrodes 81a and 82a, second comb-shaped electrodes 81b and 82b, third comb-shaped electrodes 81c and 82c surrounded by dotted lines, and reflections on both sides thereof. Electrode electrodes 81d and 82d are arranged in the surface wave propagation direction.
[0006]
In the first comb electrode 81 a of the three-electrode comb electrode 81, one of the opposing electrode fingers is connected to the output terminal 83 and the other is connected to the ground terminal 85. The first comb electrode 82 a of the three-electrode comb electrode 82 also has one of the opposing electrode fingers connected to the output terminal 84 and the other connected to the ground terminal 86.
[0007]
A surface wave is excited by applying a voltage to the first comb electrodes 81a and 82a of the three-electrode comb electrodes 81 and 82, and energy is confined by the reflector electrodes 81d and 82d, thereby forming a filter characteristic. .
[0008]
The reflector electrodes 81d and 82d were formed with a constant electrode finger width and electrode finger interval.
[0009]
[Problems to be solved by the invention]
The reflector electrode characteristic is formed by a pass frequency range with good reflection efficiency and a periodic slope characteristic on both sides thereof. Therefore, in the above configuration, the periodic characteristic of the reflector electrode appears as a waveform near the pass band, and spurious is generated. As a result, there is a problem that it is difficult to secure an attenuation near the pass frequency band.
[0010]
Therefore, an object of the present invention is to provide a surface acoustic wave filter that can sufficiently secure an attenuation near the pass frequency band.
[0011]
[Means for Solving the Problems]
To achieve this object, a surface acoustic wave filter according to the present invention includes a piezoelectric substrate, a first comb electrode provided on the piezoelectric substrate, and both sides of the first comb electrode in the surface wave propagation direction. And the first and second reflector electrodes provided so as to sandwich the second and third comb electrodes, and a plurality of the reflector electrodes are provided. The reflector electrode pitch of the electrode fingers (electrode finger width + electrode finger interval width) is divided into a plurality of reflector electrode groups, and the reflector electrode pitch differs between the reflector electrode groups. The reflector electrode pitches of the adjacent reflector electrode groups have a difference of 0.05% or more, and disturb the periodic slope characteristics near the pass frequency band of the reflector electrodes. Therefore, the above object can be achieved by suppressing spurious.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
According to the first aspect of the present invention, there is provided a piezoelectric substrate, a first comb electrode provided on the piezoelectric substrate, and first electrodes provided on both sides of the first comb electrode in the surface wave propagation direction. 2 and a third comb-shaped electrode, and first and second reflector electrodes provided so as to sandwich the second and third comb-shaped electrodes, and the reflector electrode includes a plurality of electrode fingers. The reflector electrode pitch (electrode finger width + electrode finger interval width) is constant, and is divided into a plurality of reflector electrode groups, and the reflector electrode pitch is different between each of the reflector electrode groups, and adjacent to each other. The reflector electrode pitch of the reflector electrode group is a surface acoustic wave filter having a difference of 0.05% or more , and can sufficiently secure an attenuation near the pass frequency band.
[0013]
Embodiments of the present invention will be described below with reference to the drawings.
[0014]
( Reference Example 1 )
FIG. 1 is a top view of a surface acoustic wave filter according to Reference Example 1 of the present invention.
[0015]
On the piezoelectric substrate 10, the 1st comb-shaped electrode 11 and the 2nd, 3rd comb-shaped electrodes 12 and 13 are arrange | positioned at the both sides of the surface wave propagation | transmission direction, The 1st reflector electrode 14 and those on both sides A second reflector electrode 15 is provided. The reflector electrode pitch of the first and second reflector electrodes 14 and 15 is gradually decreased as the distance from the adjacent second and third comb electrodes 12 and 13 increases.
[0016]
With this configuration, the characteristics of the first and second reflector electrodes 14 and 15 are as shown in FIG. 2, and the reflection efficiency on the low frequency side in the vicinity of the passband can be lowered as compared with the prior art.
[0017]
Further, when the reflector electrode pitch of the first and second reflector electrodes 14 and 15 is greatly changed as the distance from the adjacent second and third comb electrodes 12 and 13 increases, as shown in FIG. The reflection efficiency on the high frequency side in the vicinity of the pass band can be lowered.
[0018]
That is, the reflector electrode pitch of the first and second reflector electrodes 14 and 15 is not constant, but changes the reflection characteristics and suppresses the occurrence of spurious, thereby reducing the low frequency side or high frequency near the passband. Sufficient out-of-band attenuation on the frequency side can be ensured.
[0019]
( Reference Example 2 )
FIG. 4 is a top view of a surface acoustic wave filter according to Reference Example 2 of the present invention.
[0020]
On the piezoelectric substrate 30, the 1st comb-shaped electrode 31 and the 2nd, 3rd comb-shaped electrodes 32 and 33 are arrange | positioned on the both sides of the surface wave propagation direction, and the 1st reflector electrode 34 and the both sides are arrange | positioned. A second reflector electrode 35 is provided. The first and second reflector electrodes 34 and 35 have different reflector electrode pitches. It is composed of two reflector electrode groups (enclosed by dotted lines in FIG. 4) 34a, 34b, 35a, 35b. The reflector electrode pitch of the reflector electrode groups 34a and 35a is larger than the reflector electrode pitch of the reflector electrode groups 34b and 35b.
[0021]
FIG. 5 is a characteristic diagram of the first and second reflector electrodes 34 and 35 shown in FIG. 4, and the first reflector electrode 34 and 35 are divided into two reflector electrode groups 34a, 34b, 35a and 35b. By doing so, it is possible to reduce the reflection efficiency on the low frequency side in the vicinity of the pass band.
[0022]
Further, if the reflector electrode pitch of the reflector electrode groups 34a and 35a is made smaller than the reflector electrode pitch of the reflector electrode groups 34b and 35b, the reflection efficiency on the high frequency side in the vicinity of the pass band is lowered as shown in FIG. It is possible.
[0023]
That is, the first and second reflector electrodes 34 and 35 are divided into two or more reflector electrode groups, and the pitches of the reflection characteristics are changed by changing the pitch of each reflector electrode so that the respective periods are different. As a result, the reflector characteristics of this portion are flattened, the spurious is suppressed, and the low-frequency side or high-frequency side out-of-band attenuation near the pass band can be sufficiently secured.
[0024]
( Embodiment 1 )
FIG. 7 is a top view of the surface acoustic wave filter according to Embodiment 1 of the present invention.
[0025]
A first comb electrode 51 and second and third comb electrodes 52 and 53 are arranged on both sides of the surface wave propagation direction on the piezoelectric substrate 50, and a first reflector electrode 54 is disposed on both sides thereof. A three-electrode longitudinal mode coupled comb electrode 56 having a second reflector electrode 55 is formed. Moreover, the 1st reflector electrode 54 and the 2nd reflector electrode 55 are comprised by three reflector electrode groups 54a, 54b, 54c, 55a, 55b, 55c from which a reflector electrode pitch differs. The reflector electrode pitch of the reflector electrode groups 54a and 55a is the largest, the reflector electrode groups 54b and 55b are the largest, and the reflector electrode groups 54c and 55c are the smallest.
[0026]
Further, a three-electrode longitudinal mode coupled comb electrode 57 having the same configuration is cascade-connected to the three-electrode longitudinal mode coupled comb electrode 56.
[0027]
In the surface acoustic wave filter having such a configuration, the first and second reflections when the configurations of the reflector electrode groups 54a, 54b, 54c, 55a, 55b, and 55c are as shown in (Table 1). The characteristics of the instrument electrodes 54 and 55 are shown in FIG. FIG. 9 is an enlarged view of a main part of FIG.
[0028]
[Table 1]
Figure 0004534307
[0029]
As can be seen from FIG. 9, the reflector electrode characteristics are changed within a range in which the reflection efficiency of the reflector electrode groups 54a and 55a does not dominate the reflection efficiency of the first and second reflector electrodes 54 and 55. By doing so, it is possible to suppress the spurious on the low frequency side in the vicinity of the pass band and secure the attenuation.
[0030]
That is, it is desirable that the number of electrode fingers of the reflector electrode groups 54a and 55a be 10 to 30. Considering that the reflector electrodes 54a and 55a closest to the second and third comb electrodes 52 and 53 contribute greatly to the reflection efficiency of the first and second reflector electrodes 54 and 55, Even if the number of electrode fingers constituting the first and second reflector electrodes 54 and 55 is changed, the number of electrode fingers in the reflector electrode groups 54a and 55a is preferably 10 to 30.
[0031]
Further, when the number of electrode fingers of the reflector electrode groups 54a and 55a exceeds 30 ((d) in FIG. 9), the reflection efficiency of the reflector electrode groups 54a and 55a becomes dominant, and the first and second It becomes difficult to suppress the spurious near the passband by changing the characteristics of the reflector electrodes 54 and 55. On the other hand, when the number of electrode fingers of the reflector electrode groups 54a and 55a is 9 or less, the reflection efficiency is insufficient and it is difficult to secure desired characteristics.
[0032]
Next, the reflector electrode pitch of the reflector electrode groups 54a and 55a is λa, the reflector electrode pitch of the reflector electrode groups 54b and 55b is λb, and the reflector pitch of the reflector electrode groups 54c and 55c is λc (Table 2). FIG. 10 shows the characteristics of the first and second reflector electrodes 54 and 55 in the configuration as shown in FIG.
[0033]
[Table 2]
Figure 0004534307
[0034]
As can be seen from FIG. 10, in order to secure attenuation on the low frequency side in the vicinity of the pass band, the reflector electrode pitch is larger as it is closer to the second and third comb-shaped electrodes 52 and 53, and is adjacent to each other. The reflector pitch with respect to the reflector electrode group is 0.05% or more, preferably 0.1% or more, and the reflector electrodes have a long distance from the second and third comb electrodes 52 and 53. The reflector electrode pitch should be made smaller for groups.
[0035]
In the first embodiment , the first and second reflector electrodes 54 and 55 are each divided into a plurality of reflector electrode groups, and the distance from the second and third comb electrodes 52 and 53 is long. The reflector electrode pitch was made smaller in the reflector electrode group to suppress the low frequency side spurious near the pass band, and the attenuation was ensured. In order to secure the attenuation amount on the high frequency side, the reflector electrode pitch may be increased as the reflector electrode group has a longer distance from the second and third comb electrodes 52 and 53.
[0036]
Although only the three-electrode longitudinal mode coupled comb electrode 56 has been described, the same applies to the three-electrode longitudinal mode coupled comb electrode 57 having the same configuration.
[0037]
Furthermore, in the third embodiment, the surface acoustic wave filter in which a plurality of two three-electrode longitudinal mode coupled comb electrodes 56 and 57 are connected in cascade has been described. However, as shown in FIGS. Also for the surface acoustic wave filter composed of three-electrode longitudinal mode coupled comb electrodes, the first and second reflector electrodes of the respective three-electrode longitudinal mode coupled comb electrodes are constructed as in the first embodiment. Thus, the same effect can be obtained.
[0038]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a surface acoustic wave filter that suppresses spurious in the vicinity of the pass frequency band and has a sufficient out-of-band attenuation. Therefore, it is possible to improve the performance and simplify the circuit of a wireless device such as a mobile phone using the surface acoustic wave filter.
[Brief description of the drawings]
1 is a top view of a surface acoustic wave filter in Reference Example 1 of the present invention. FIG. 2 is a frequency characteristic curve diagram of the surface acoustic wave filter shown in FIG. 1. FIG. 3 is a surface acoustic wave filter in Reference Example 1 of the present invention. FIG. 4 is a top view of the surface acoustic wave filter in Reference Example 2 of the present invention. FIG. 5 is a frequency characteristic curve diagram of the surface acoustic wave filter shown in FIG. 4. FIG. 6 is a reference example 2 of the present invention. frequency characteristic curve of the surface acoustic wave filter in definitive first embodiment of a top view of a SAW filter in the first embodiment of the frequency characteristic diagram [7] the present invention of the surface acoustic wave filter 8 the invention FIG. 9 is an enlarged view of the main part of FIG. 8. FIG. 10 is a frequency characteristic curve diagram of the surface acoustic wave filter according to the first embodiment of the present invention. Above the surface acoustic wave filter Figure [Description of the code]
DESCRIPTION OF SYMBOLS 10 Piezoelectric substrate 11 1st comb electrode 12 2nd comb electrode 13 3rd comb electrode 14 1st reflector electrode 15 2nd reflector electrode 30 Piezoelectric substrate 31 1st comb electrode 32 1st Two comb-shaped electrodes 33 Third comb-shaped electrode 34 First reflector electrode 34a Reflector electrode group 34b Reflector electrode group 35 Second reflector electrode 35a Reflector electrode group 35b Reflector electrode group 50 Piezoelectric substrate 51 First comb electrode 52 Second comb electrode 53 Third comb electrode 54 First reflector electrode 54a Reflector electrode group 54b Reflector electrode group 54c Reflector electrode group 55 Second reflector electrode 55a Reflector electrode group 55b Reflector electrode group 55c Reflector electrode group 56 Three-electrode longitudinal mode coupled comb electrode 57 Three-electrode longitudinal mode coupled comb electrode

Claims (2)

圧電基板と、この圧電基板上に設けた第１の櫛型電極と、この第１の櫛型電極のその表面波伝搬方向の両側に設けた第２、第３の櫛型電極と、この第２及び第３の櫛型電極を挟むように設けた第１及び第２の反射器電極とを備え、前記反射器電極は複数本の電極指の反射器電極ピッチ（電極指幅＋電極指間隔幅）が一定となる、複数の反射器電極群に分けられ、それぞれの前記反射器電極群の間で前記反射器電極ピッチが異なり、隣り合う前記反射器電極群の反射器電極ピッチ同士は、０．０５％以上の差を有している弾性表面波フィルタ。A piezoelectric substrate; a first comb electrode provided on the piezoelectric substrate; second and third comb electrodes provided on both sides of the first comb electrode in the surface wave propagation direction; First and second reflector electrodes provided so as to sandwich the second and third comb electrodes, and the reflector electrode has a reflector electrode pitch of a plurality of electrode fingers (electrode finger width + electrode finger interval). Width) is constant, and is divided into a plurality of reflector electrode groups, the reflector electrode pitch is different between each of the reflector electrode groups, the reflector electrode pitch of the adjacent reflector electrode groups, A surface acoustic wave filter having a difference of 0.05% or more . 前記櫛型電極に隣接する前記反射器電極群の電極指の本数を１０本から３０本で構成した請求項１記載の弾性表面波フィルタ。The surface acoustic wave filter according to claim 1, wherein the number of electrode fingers of the reflector electrode group adjacent to the comb-shaped electrode is 10 to 30.
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