JP3780496B2

JP3780496B2 - Surface acoustic wave filter

Info

Publication number: JP3780496B2
Application number: JP2001133634A
Authority: JP
Inventors: 宏明前原; 祐司水谷
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 2000-06-30
Filing date: 2001-04-27
Publication date: 2006-05-31
Anticipated expiration: 2021-04-27
Also published as: JP2002232265A

Description

【０００１】
【発明の属する技術分野】
本発明は、圧電基板上に複数の弾性表面波電極をラダー型に構成してなる弾性表面波フィルタに関し、特に、フィルタの通過帯域における低域側の肩特性を改善した弾性表面波フィルタに関する。
【０００２】
【従来の技術】
移動体通信機器において、高周波用の帯域フィルタとして、複数の弾性表面波電極を圧電基板上に構成してなる弾性表面波フィルタが知られている。例えば、特開平５−１８３３８０号公報には、圧電基板上に複数の弾性表面波電極によりラダー型フィルタ回路を構成した弾性表面波フィルタが開示されている。
【０００３】
図８は、上記先行技術に開示されている弾性表面波フィルタを説明するための模式的な回路図である。
従来の弾性表面波フィルタ５１０は、矩形の圧電基板５２０を用いて構成されている。圧電基板５２０上には、弾性表面波電極（不図示）からなる共振子５３０，５４０，５５０，５６０が配設されている。すなわち、図に示すように、入力端子５７０と出力端子５８０との間に構成される直列腕において共振子５３０，５４０が直列に接続されている（各共振子５３０，５４０を直列共振子と称す。また、共振子５３０，５４０を併せて直列共振子群と称す。以下同じ。）。また、直列腕とグランド電極５９０との間に、共振子５５０，５６０が並列に接続されている（各共振子５５０，５６０を並列共振子と称す。また、共振子５５０，５６０を併せて並列共振子群と称す。以下、同じ。）。なお、直列共振子５３０，５４０と並列共振子５５０，５６０とは入出力間において交互に配置されており、各並列共振子５５０，５６０は夫々インダクタンス５５５，５６５を介してグランド電極５９０に接続されている。
この直列共振子５３０と並列共振子５５０の１組で１段のラダー型フィルタを構成しており、同様に直列共振子５４０と並列共振子５６０の１組で１段のラダー型フィルタを構成している。
【０００４】
従来の弾性表面波フィルタ５１０の動作原理は以下の通りである。図９は直列・並列共振子５３０〜５６０を形成する各弾性表面波電極の構造を説明する図である。図では１ポート型弾性表面波共振子の電極部分のみが模式的に示されている。
【０００５】
図において、７００は弾性表面波電極である。弾性表面波電極７００は中央に配置されたＩＤＴ７１０の両側に反射器７２０，７３０を配置した構造を有する。
ＩＤＴ７１０は、複数の電極指７１１を有する櫛歯状電極７１０ａと、複数の電極指７１２を有する櫛歯状電極７１０ｂとを、互いの電極指７１１，７１２が間挿し合うように交叉して配置した構造を有する。なお、例えば、櫛歯状電極７１０ａは入出力電極に接続され、また櫛歯状電極７１０ｂはグランド電極に接続される。
【０００６】
このような構造の弾性表面波電極７００のＩＤＴ７１０に入力された信号により励振された表面波が、反射器７２０，７３０で反射されて定在波とされ、反射器７２０，７３０間に閉じ込められ高いＱ値を有する共振子として動作する。この弾性表面波電極７００のインピーダンス特性においては、周知のように、共振周波数でインピーダンスが低くなる極が存在し、反共振周波数においてインピーダンスが高くなる極が現れる共振特性を有するようになる。
【０００７】
このような構造の直列・並列共振子５３０〜５６０を有した弾性表面波フィルタ５１０では、弾性表面波電極７００のインピーダンス特性を利用して所望の帯域幅を有する通過帯域を得ている。すなわち、各直列共振子５３０，５４０の共振周波数と、各並列共振子５５０，５６０の反共振周波数とを略一致させることにより、この間の周波数付近において入出力インピーダンスを特性インピーダンスと整合させており、それによって通過帯域を構成している。特にラダー型フィルタ回路では、弾性表面波電極７００は所定のインピーダンス特性を有するため、直列共振子５３０，５４０の反共振周波数付近では非常に高インピーダンスとなり、逆に並列共振子５５０，５６０の共振周波数付近では非常に低インピーダンスとなるため、この特性を利用してラダー型フィルタ回路では、高域側の阻止域から通過帯域を介して低域側の阻止域を形成した幅広のフィルタ特性を得ることになる。
【０００８】
このようなラダー型フィルタ回路において減衰極の減衰量を改善する方法として共振子に弾性表面波電極で形成したＬＣ回路を設けたり（特開平９−２３２９０６）、外部接続時のワイヤ長を変えることでワイヤ自体のもつインダクタンス値を変化させ減衰極の位置を変え減衰量を調整する（特開平１１−５５０６７）技術が開示されている。
【０００９】
【発明が解決しようとする課題】
しかしながら、近年の移動体通信システムにおいては、電波の有効利用のために規格が決められており、例えば、米国のＰＣＳ規格では受信帯域が１９３０〜１９９０ＭＨｚ、送信帯域が１８５０〜１９１０ＭＨｚ、送受信フィルタの通過帯域同士の間隔は２０ＭＨｚとなり、受信帯域に隣接して送信帯域が形成されているため、受信用フィルタにおいては、広帯域を維持しつつ、充分な減衰量と通過帯域における低挿入損失を確保することが必要となる。従って、隣接する受信帯域の低域側（左肩側）において阻止域から通過帯域の急峻な特性が必要となるが、上述の特開平９−２３２９０６や特開平１１−５５０６７の何れの技術でもってしてもフィルタ特性における広帯域化・左肩側の急峻化の達成は困難であった。
【００１０】
本発明は上述の課題に鑑みて案出されたものであり、その目的は、特別なＬＣ回路等がなくても、広域化を維持しつつ、フィルタの通過帯域における低域側の急峻性を十分取ることができる弾性表面波フィルタを提供することにある。
【００１１】
【課題を解決するための手段】
上述の課題を解決するために本発明は、圧電基板の表面に、入力端子と出力端子との間に複数の弾性表面波電極が直列接続された直列共振子群と、直列共振子群の各弾性表面波電極の入力端子側あるいは出力端子側とグランドとの間に複数の弾性表面波電極が並列に接続された並列共振子群とを配すると共に、直列共振子群の弾性表面波電極で形成される共振周波数と並列共振子群の弾性表面波電極で形成される反共振周波数を略一致させることでフィルタの通過帯域を形成した弾性表面波フィルタにおいて、
前記並列共振子群の弾性表面波電極のうち、一部の弾性表面波電極は、得られるＱ値を他の弾性表面波電極で得られるＱ値よりも劣化させたＱ値劣化構造とすると共に、前記一部の弾性表面波電極で形成する共振周波数が他の並列共振子群の弾性表面波電極で形成する反共振周波数よりも低く、かつ他の並列共振子群の弾性表面波電極で形成する共振周波数よりも高くしたことを特徴とする弾性表面波フィルタを提供する。
【００１２】
本発明の構成によれば、前記一部の弾性表面波電極はＱ値劣化構造とし、その共振周波数が、他の並列共振子群の弾性表面波電極で形成する反共振周波数よりも低く、かつ他の並列共振子群の弾性表面波電極で形成する共振周波数よりも高くしたために、フィルタ特性において低域側の減衰極から通過帯域に入るまでの間に新たな減衰極が形成され、これによりフィルタの通過帯域が広帯域を確保しつつ、通過帯域の低域側の急峻度が大きくなり十分な肩特性を確保する事が可能となる。
【００１３】
【発明の実施の形態】
以下に、本発明の実施例について図面を用いて説明する。
図１は本発明の実施の形態に係る弾性表面波フィルタの構造を示す図であり、図２は本発明の特徴を説明するための並列共振子の拡大図である。
図１において弾性表面波フィルタＡは、圧電基板１の主面に、入力端子（ＩＮ）と出力端子（ＯＵＴ）との間に複数の弾性表面波電極５４，５５，５６が直列に接続された直列共振子群と、弾性表面波電極５７，５８，５９，６０が入出力端子（ＩＮ，ＯＵＴ）とグランド（ＧＮＤ）に対して並列に接続された並列共振子群が形成されている。以下、直列共振子群の弾性表面波電極５４〜５６の夫々を直列共振子と称し、並列共振子群の弾性表面波電極５７〜６０の夫々を並列共振子と称す。
【００１４】
直列共振子群の弾性表面波電極５４，５５，５６及び並列共振子群の弾性表面波電極５７，５８，５９，６０は、何れも中央に櫛歯状のインターデジタルトランスデューサ（以下、ＩＤＴ）５４ａ〜６０ａを有し、その両側に反射器５４ｂ，５４ｃ，５５ｂ，５５ｃ・・・６０ｂ，６０ｃを形成した構造を有する。
【００１５】
圧電基板１は所定カット角、所定伝搬方向となるように矩形状に切断処理された水晶、ニオブ酸リチウム、タンタル酸リチウム、四ホウ酸リチウム等から成る。
また、弾性表面波電極５４，５５，５６及び弾性表面波電極５７，５８，５９，６０は、例えば、アルミニウム薄膜からなり、その厚みは０．1〜０．３μmで所定のパターンに被着形成されている。また、ＩＤＴ５４ａ〜６０ａ及びその両側の反射器５４ｂ，５４ｃ，５５ｂ，５５ｃ・・・６０ｂ，６０ｃの電極指幅及び電極指間隔は、例えば、弾性表面波の波長λに対して略１／４λとなっている。
【００１６】
ＩＤＴ５４ａ〜６０ａの構造としては、例えば、並列共振子群の弾性表面波電極５７〜６０のＩＤＴ５７ａ〜６０ａの構造は図２（ａ）（ｂ）に示すように、電極指Ａ１及びそれに交叉する電極指Ａ２が互いに交叉して配設されており、発生する弾性表面波の伝搬方向に直交して整列しており、例えば、電極指Ａ１及び電極指Ａ２の電極幅Ｐｗと各電極指Ａ１、Ａ２の電極指間隔Ｐｐは略同じ長さに設定されている。なお、本実施例では電極幅Ｐｗと電極指間隔Ｐｐの長さは略同じに設定したが、必ずしもこれに限定されるものではなく、電極幅Ｐｗと電極指間隔Ｐｐの長さを異ならせたとしても本発明の同様の効果を得ることができる。
【００１７】
６１は入力端子であり、６２は出力端子である。入力端子６１から直列にＩＤＴ５４ａ〜５６ａが接続され出力端子６２につながっている。これらにＩＤＴ５７ａ〜６０ａの一方側が各反射器５７ｂ，５８ｃ，５９ｃ，６０ｂを通じて接続されており、他方側が各反射器５７ｃ，５８ｂ，５９ｂ，６０ｃにより各グランド電極（ＧＮＤ）に接続されている。
【００１８】
ここで、本発明では、図３に示すように、並列共振子群の弾性表面波電極５７〜６０の内、弾性表面波電極６０は、得られるＱ値を劣化させるＱ値劣化構造となっている。更に、Ｑ値劣化構造に加えて、弾性表面波電極６０の共振周波数Ｆｒが並列共振子群の弾性表面波電極５７〜５９の反共振周波数Ｆａよりも低く、かつ弾性表面波電極５７〜５９の共振周波数Ｆｒよりも高くになるようにした。
【００１９】
ここで、Ｑ値は一般的にＱ＝２πＦＬ／Ｒ（Ｆ：共振周波数Ｌ：インダクタンスＲ：共振抵抗）としてあらわされるが、本発明は、弾性表面波電極６０の共振周波数Ｆｒがフィルタの通過帯域に近く、かつ弾性表面波電極６０で得られるＱ値を低くすることで通過帯域の左肩を急峻なものにすることを見出したものである。
【００２０】
Ｑ値を劣化させる程度としては、弾性表面波電極６０の共振周波数Ｆｒでのインピーダンスが弾性表面波電極５７〜５９の共振特性中で共振周波数Ｆｒと反共振周波数Ｆａで結ばれる軌跡に近づくように共振特性の挿入損失を劣化させると良い。
【００２１】
Ｑ値劣化構造としては、共振抵抗Ｒを高くするように形成すれば良く、高くするためには以下のような具体的構成とすると良い。
具体的に、弾性表面波電極６０の各電極指Ａ１、Ａ２の対数が弾性表面波電極５７〜５９の各電極指Ａ１、Ａ２の対数に比べて少なくすることで共振抵抗Ｒが高くなりＱ値を劣化させることができる。
また、弾性表面波電極６０の各電極指Ａ１、Ａ２同士が交叉した長さＰｘが他の弾性表面波電極５７〜５９の各電極指同士が交叉した長さＰｘに比べて短くすることで共振抵抗Ｒを高くしてＱ値を劣化させることができる。
【００２２】
さらに、図４に示すように、弾性表面波電極６０１は櫛歯状電極から形成されたサブ電極６１、６２から構成され、そのサブ電極６１、６２が互いに直列に接続されている。この櫛歯状電極からなるサブ電極６１は一方が入力端子（ＩＮ）と出力端子（ＯＵＴ）を結ぶ線に接続される電極６１ａと、電極６１ａに対向する電極６１ｂと、電極６１ａに接続するサブ電極６２の一方の電極６２ａと、電極６２ａに対向してグランド側に接続される電極６２ｂとが直列に接続されている。この直列接続のため、共振抵抗Ｒが図１の弾性表面波電極６０に比べて高くなり、Ｑ値を劣化させることができる。
【００２３】
一方、弾性表面波電極６０で形成する共振周波数Ｆｒが他の並列共振子群の弾性表面波電極５７〜５９で形成する反共振周波数Ｆａよりも低く、かつ他の並列共振子群の弾性表面波電極５７〜５９で形成する共振周波数Ｆｒよりも高くする為の手段としては、図２に示すように、並列共振子群の弾性表面波電極５７〜６０の電極指の幅Ｐｗと各電極指同士の電極指間隔Ｐｐで構成する電極指ピッチを、弾性表面波電極６０よりも他の弾性表面波電極５７〜５９が長くなるように形成するとよい。この場合、電極指ピッチを変えるのは、並列共振子群の弾性表面波電極５７〜６０の各電極指の幅Ｐｗを略同じとし、各電極指同士の電極指間隔Ｐｐを変更する方法、各電極指同士の電極指間隔Ｐｐを略同じとし、各電極指の幅Ｐｗを変える方法及び並列共振子群の弾性表面波電極５７〜６０の各電極指の幅Ｐｗを変更し、かつ各電極指同士の電極指間隔Ｐｐを変更する方法があげられる。
【００２４】
また、弾性表面波電極６０のメタライゼーションレシオ（電極指ピッチに対する電極指幅Ｐｗの比をいう。以下同じ）よりも他の並列共振子群の弾性表面波電極５７〜５９のメタライゼーションレシオが大きくなるように形成する方法がある。例えば、図２（ａ）に示す弾性表面波電極５７〜５９について、電極指Ａ１、Ａ２の電極指幅をＰｗ＝０．５００μm、電極指間隔Ｐｐ＝０．５００μmとし、図２（ｂ）に示す弾性表面波電極６０について、電極指幅をＰｗ＝０．４００μm、電極指間隔Ｐｐ＝０．６００μmとすることで、得られる共振周波数を異ならせることができる。
【００２５】
また、他の方法としては、弾性表面波電極６０の電極厚みを他の並列共振子群の弾性表面波電極５７〜５９の電極厚みに比べて薄くしても良い。
【００２６】
なお、上述では並列共振子群の１つの弾性表面波電極６０で並列共振子群の他の弾性表面波電極５７〜５９により形成される減衰極よりも高周波側に極を形成しているが、これに限定されることはなく並列共振子群の２つ以上の弾性表面波電極で形成してもよい。このような構成にしても同様の効果が得られる。
【００２７】
かくして、本発明の弾性表面波フィルタＡによれば、従来、並列共振子群の弾性表面波電極５７〜６０の減衰極が通過帯域の低域側の減衰極を形成するのに用いていたのに対して、並列共振子群の一つの弾性表面波電極６０をＱ値劣化構造とすると共に、その共振周波数Ｆｒが、他の弾性表面波電極５７〜５９の反共振周波数Ｆａよりも低く、かつ他の弾性表面波電極５７〜５９の共振周波数Ｆｒよりも高くなるようにしたために、フィルタ特性において低域側の減衰極から通過帯域に入るまでの間で新たにもう１つの極が形成され、これによりフィルタの通過帯域が広帯域を確保しつつ、通過帯域の低域側の急峻度が大きくなり十分な肩特性を確保する事が可能となる。しかも、通過帯域減衰特性はほとんど変化しないため、従来の設計方法はそのまま使用できるものである。
【００２８】
また、従来は外部引きまわし電極であるアルミ線ワイヤや金線ワイヤのワイヤ長を変えることでワイヤのもつインダクタンス値を変えて低域側の減衰域の減衰量を確保しており結線状態により極の位置が微妙にずれ、特性検査の歩留まりを落とす原因になっていたが、本発明によれば、そのようなものを利用せずに通過帯域低域側肩特性を急峻にできるため安定した歩留まりも確保できるものである。
【００２９】
【実施例】
次に本発明の作用効果を確認するために本発明の実施例を示す。
（実施例１）
圧電基板１としては４２°Ｙ−Ｘタンタル酸リチウム基板を用い、その表面にＡｌまたはＡｌ合金からなる直列共振子の弾性表面波電極５４，５５，５６及び並列共振子の弾性表面波電極５７，５８，５９，６０を図１の配線のように形成した。これにより、中心周波数１．９６ＧＨｚのラダー型ＳＡＷフィルタを製作した。
【００３０】
この場合、直列共振子の弾性表面波電極５４，５５，５６の交叉幅ＰｘはＰｘ＝１０〜１５λ、並列共振子の弾性表面波電極５７，５８，５９の交叉幅Ｐｘは何れもＰｘ＝３０λ、弾性表面波電極６０の交差幅ＰｘはＰｘ＝２０λとした。また、直列共振子の弾性表面波電極５４，５５，５６の電極対数を９５対、並列共振子の弾性表面波電極５７，５８，５９の電極対数を４５対、弾性表面波電極６０の電極対数を１５対としている。
また、弾性表面波電極５７、５８，５９の電極指幅Ｐｗ及び電極指間隔Ｐｐの双方を、Ｐｐ、Ｐｗ＝０．５０３μｍとし弾性表面波電極６０の電極指幅Ｐｗと電極指間隔Ｐｐの双方をＰｗ、Ｐｐ＝０．５００μｍとして弾性表面波電極５７〜５９よりも電極指ピッチを短くした。なお、直列共振子の弾性表面波電極５４、５５、５６の電極指幅Ｐｗと電極指間隔Ｐｐの双方をＰｐ、Ｐｗ＝０．４８４５μｍとし、電極幅Ｐｗ及び電極指間隔Ｐｐは同じ長さに設定されている。
【００３１】
このように形成した弾性表面波フィルタＡのフィルタ特性を図５に示す。このとき、図５の縦軸は減衰量（５ｄＢ／ｄｉｖ）であり、横軸は規格化周波数（中心周波数ｆ０：１９６０ＭＨｚ、span：１９６ＭＨｚ）である。
【００３２】
図５において０．９７近傍に並列共振子の弾性表面波電極５７〜５９による減衰極が形成されている。さらに、１．０４近傍に直列共振子の弾性表面波電極５４，５５，５６による減衰極が形成されている。
【００３３】
図５に示すように、通過帯域低域側の極の高周波側に並列共振子の弾性表面波電極６０による減衰極Ｂが形成されることで低域側の通過域肩特性が急峻となり通過域特性が広帯域となっていることがわかる。
これに対し比較例として、直列共振子の弾性表面波電極５４，５５，５６の交叉幅Ｐｘは何れもＰｘ＝１０〜１５λ、並列共振子の弾性表面波電極５７〜６０の交叉幅Ｐｘは何れもＰｘ＝３０λとして同じ長さに形成し、また並列共振子の弾性表面波電極５７〜６０のＰｗおよびＰｐは何れもＰｗ，Ｐｐ＝０．５０３μｍとした。
また、直列共振子の弾性表面波電極５４，５５，５６の電極対数を９５対、並列共振子の弾性表面波電極５７〜６０の電極対数を４５対とし、電極幅Ｐｗ及び電極指間隔Ｐｐを同じ長さに設定した比較例の弾性表面波フィルタを形成してフィルタ特性を図６に示した。図６の縦軸も減衰量（５ｄＢ／ｄｉｖ）であり、横軸は規格化周波数（中心周波数ｆ０：１９６０ＭＨｚ、span：１９６ＭＨｚ）とする。
このフィルタ特性によれば、通過帯域の低域側肩特性のスペックを十分満足するものが得られてないことがわかる。
（実施例２）
図1で示す弾性表面波電極６０を図４で示す弾性表面波電極６０１（直列に接続されたサブ電極６１、６２の構造）とする以外は実施例１と同一条件で実験を行った。なお、サブ電極６１、６２の何れもが交叉幅ＰｘはＰｘ＝２０λ、電極指幅Ｐｗ及び電極指間隔Ｐｐの双方をＰｐ、Ｐｗ＝０．５μｍとした。また、電極対数を４５対としている。
このように実験されたフィルタ特性を図７に示す。この結果でもサブ電極６１，６２で構成される直列共振子の弾性表面波電極６０１が図1で示した弾性表面波電極６０に比べて共振抵抗が増加して弾性表面波電極６０１のＱ値が他の並列共振子群の弾性表面波電極５７〜５９のＱ値に比べて劣化しており、さらに弾性表面波電極６０の共振周波数を、弾性表面波電極５７〜５９の反共振周波数よりも低く、かつ弾性表面波電極５７〜５９の共振周波数よりも高くしているので、通過帯域の左肩に新たな減衰極が発生し、通過帯域の低域側の急峻度が大きくなっていることが理解できる。
【００３４】
【発明の効果】
本発明の構成によれば、一部の弾性表面波電極はＱ値劣化構造とし、その共振周波数を、他の弾性表面波電極の反共振周波数よりも低く、かつ他の弾性表面波電極の共振周波数よりも高くしたために、フィルタ特性において低域側の減衰極から通過帯域に入るまでの間に新たな減衰極が形成され、これによりフィルタの通過帯域が広帯域を確保しつつ、通過帯域の低域側の急峻度が大きくなり十分な肩特性を確保する事が可能となる弾性表面波フィルタを提供できる。
【図面の簡単な説明】
【図１】本発明の弾性表面波フィルタの平面図である。
【図２】（ａ）は弾性表面波電極５７〜５９を示す図、（ｂ）は弾性表面波電極６０の構成を示す図である。
【図３】本発明の弾性表面波電極５７〜５９と弾性表面波電極６０との共振特性を示す図である。
【図４】本発明の他の弾性表面波フィルタを説明する回路図である。
【図５】本発明のフィルタ特性を示す特性図である。
【図６】比較例のフィルタ特性を示す特性図である。
【図７】本発明の他の弾性表面波フィルタにおいてのフィルタ特性を示す特性図である。
【図８】従来の弾性表面波フィルタを説明するための模式的平面図である。
【図９】１ポート型弾性表面波電極を説明するための拡大平面図である。
【符号の説明】
Ａ：弾性表面波フィルタ
１：圧電基板
５４〜５６：直列共振子の弾性表面波電極
５７〜６０：並列共振子の弾性表面波電極
６１：入力端子
６２：出力端子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave filter in which a plurality of surface acoustic wave electrodes are formed in a ladder shape on a piezoelectric substrate, and more particularly to a surface acoustic wave filter having improved low-side shoulder characteristics in the pass band of the filter.
[0002]
[Prior art]
In mobile communication devices, a surface acoustic wave filter having a plurality of surface acoustic wave electrodes formed on a piezoelectric substrate is known as a high-frequency bandpass filter. For example, Japanese Patent Laid-Open No. 5-183380 discloses a surface acoustic wave filter in which a ladder type filter circuit is configured by a plurality of surface acoustic wave electrodes on a piezoelectric substrate.
[0003]
FIG. 8 is a schematic circuit diagram for explaining the surface acoustic wave filter disclosed in the prior art.
A conventional surface acoustic wave filter 510 is configured using a rectangular piezoelectric substrate 520. On the piezoelectric substrate 520, resonators 530, 540, 550, and 560 made of surface acoustic wave electrodes (not shown) are disposed. That is, as shown in the figure, the resonators 530 and 540 are connected in series in the series arm formed between the input terminal 570 and the output terminal 580 (each resonator 530 and 540 is referred to as a series resonator). In addition, the resonators 530 and 540 are collectively referred to as a series resonator group (the same applies hereinafter). Further, resonators 550 and 560 are connected in parallel between the series arm and the ground electrode 590 (the resonators 550 and 560 are referred to as parallel resonators. The resonators 550 and 560 are also combined in parallel. This is referred to as a resonator group. Series resonators 530 and 540 and parallel resonators 550 and 560 are alternately arranged between the input and output, and each parallel resonator 550 and 560 is connected to ground electrode 590 via inductances 555 and 565, respectively. ing.
A single-stage ladder filter is configured by one set of the series resonator 530 and the parallel resonator 550, and similarly, a single-stage ladder filter is configured by one set of the series resonator 540 and the parallel resonator 560. ing.
[0004]
The operation principle of the conventional surface acoustic wave filter 510 is as follows. FIG. 9 is a diagram for explaining the structure of each surface acoustic wave electrode forming the series / parallel resonators 530 to 560. In the figure, only the electrode portion of the 1-port surface acoustic wave resonator is schematically shown.
[0005]
In the figure, reference numeral 700 denotes a surface acoustic wave electrode. The surface acoustic wave electrode 700 has a structure in which reflectors 720 and 730 are disposed on both sides of an IDT 710 disposed in the center.
In the IDT 710, a comb-like electrode 710a having a plurality of electrode fingers 711 and a comb-like electrode 710b having a plurality of electrode fingers 712 are arranged so that the electrode fingers 711 and 712 are interleaved with each other. It has a structure. For example, the comb-like electrode 710a is connected to the input / output electrode, and the comb-like electrode 710b is connected to the ground electrode.
[0006]
The surface wave excited by the signal input to the IDT 710 of the surface acoustic wave electrode 700 having such a structure is reflected by the reflectors 720 and 730 to be a standing wave, and is confined between the reflectors 720 and 730 and is high. It operates as a resonator having a Q value. As is well known, the impedance characteristic of the surface acoustic wave electrode 700 has a resonance characteristic in which there is a pole whose impedance decreases at the resonance frequency and a pole whose impedance increases at the anti-resonance frequency.
[0007]
In the surface acoustic wave filter 510 having the series / parallel resonators 530 to 560 having such a structure, a pass band having a desired bandwidth is obtained using the impedance characteristic of the surface acoustic wave electrode 700. That is, by making the resonance frequency of each of the series resonators 530 and 540 substantially coincide with the anti-resonance frequency of each of the parallel resonators 550 and 560, the input / output impedance is matched with the characteristic impedance in the vicinity of the frequency therebetween. Thereby, a pass band is formed. In particular, in the ladder type filter circuit, the surface acoustic wave electrode 700 has a predetermined impedance characteristic, so that it has a very high impedance in the vicinity of the antiresonance frequency of the series resonators 530 and 540, and conversely, the resonance frequency of the parallel resonators 550 and 560. Since the impedance is very low in the vicinity, a ladder-type filter circuit that uses this characteristic can obtain a wide filter characteristic that forms a low-frequency stopband from the high-frequency stopband via the passband. become.
[0008]
In such a ladder type filter circuit, as a method of improving the attenuation amount of the attenuation pole, an LC circuit formed by a surface acoustic wave electrode is provided in the resonator (Japanese Patent Laid-Open No. 9-232906), or the wire length at the time of external connection is changed. The technique of adjusting the attenuation amount by changing the position of the attenuation pole by changing the inductance value of the wire itself (Japanese Patent Laid-Open No. 11-55067) is disclosed.
[0009]
[Problems to be solved by the invention]
However, in recent mobile communication systems, standards have been determined for effective use of radio waves. For example, in the US PCS standard, a reception band is 1930 to 1990 MHz, a transmission band is 1850 to 1910 MHz, and a transmission filter is passed. The interval between the bands is 20 MHz, and a transmission band is formed adjacent to the reception band. Therefore, in the reception filter, a sufficient attenuation amount and a low insertion loss in the pass band should be ensured while maintaining a wide band. Is required. Therefore, a steep characteristic of the pass band from the stop band is required on the low band side (left shoulder side) of the adjacent reception band. However, any of the above-mentioned techniques of Japanese Patent Laid-Open Nos. 9-232906 and 11-55067 is used. However, it has been difficult to achieve a broader filter characteristic and a sharper left shoulder.
[0010]
The present invention has been devised in view of the above-mentioned problems, and the object thereof is to reduce the steepness on the low band side in the pass band of the filter while maintaining a wide area without a special LC circuit or the like. An object of the present invention is to provide a surface acoustic wave filter that can be sufficiently taken.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a series resonator group in which a plurality of surface acoustic wave electrodes are connected in series between an input terminal and an output terminal on the surface of a piezoelectric substrate, and each of the series resonator groups A parallel resonator group in which a plurality of surface acoustic wave electrodes are connected in parallel is arranged between the input terminal side or output terminal side of the surface acoustic wave electrode and the ground. In the surface acoustic wave filter in which the passband of the filter is formed by substantially matching the resonance frequency formed and the anti-resonance frequency formed by the surface acoustic wave electrodes of the parallel resonator group,
Among the surface acoustic wave electrodes of the group of parallel resonators, some of the surface acoustic wave electrodes have a Q value deterioration structure in which the obtained Q value is deteriorated more than the Q value obtained by other surface acoustic wave electrodes. The resonance frequency formed by the partial surface acoustic wave electrodes is lower than the anti-resonance frequency formed by the surface acoustic wave electrodes of the other parallel resonator groups, and is formed by the surface acoustic wave electrodes of the other parallel resonator groups. A surface acoustic wave filter characterized by having a resonance frequency higher than the resonance frequency is provided.
[0012]
According to the configuration of the present invention, the some surface acoustic wave electrodes have a Q value degradation structure, and a resonance frequency thereof is lower than an anti-resonance frequency formed by the surface acoustic wave electrodes of other parallel resonator groups, and Since it is higher than the resonance frequency formed by the surface acoustic wave electrodes of other parallel resonator groups, a new attenuation pole is formed in the filter characteristics before entering the passband from the low-frequency side attenuation pole. While the pass band of the filter is ensured to be wide, the steepness on the low band side of the pass band is increased and sufficient shoulder characteristics can be ensured.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing the structure of a surface acoustic wave filter according to an embodiment of the present invention, and FIG. 2 is an enlarged view of a parallel resonator for explaining the features of the present invention.
1, the surface acoustic wave filter A has a plurality of surface acoustic wave electrodes 54, 55, and 56 connected in series between the input terminal (IN) and the output terminal (OUT) on the main surface of the piezoelectric substrate 1. A series resonator group and a parallel resonator group in which the surface acoustic wave electrodes 57, 58, 59, 60 are connected in parallel to the input / output terminals (IN, OUT) and the ground (GND) are formed. Hereinafter, each of the surface acoustic wave electrodes 54 to 56 of the series resonator group is referred to as a series resonator, and each of the surface acoustic wave electrodes 57 to 60 of the parallel resonator group is referred to as a parallel resonator.
[0014]
The surface acoustic wave electrodes 54, 55, 56 of the series resonator group and the surface acoustic wave electrodes 57, 58, 59, 60 of the parallel resonator group are all comb-shaped interdigital transducers (hereinafter referred to as IDTs) 54a at the center. ˜60a, and reflectors 54b, 54c, 55b, 55c... 60b, 60c are formed on both sides thereof.
[0015]
The piezoelectric substrate 1 is made of quartz, lithium niobate, lithium tantalate, lithium tetraborate or the like cut into a rectangular shape so as to have a predetermined cut angle and a predetermined propagation direction.
The surface acoustic wave electrodes 54, 55, and 56 and the surface acoustic wave electrodes 57, 58, 59, and 60 are made of, for example, an aluminum thin film and have a thickness of 0.1 to 0.3 μm and are deposited in a predetermined pattern. Has been. Further, the electrode finger width and electrode finger interval of the IDTs 54a to 60a and the reflectors 54b, 54c, 55b, 55c... 60b, 60c on both sides thereof are, for example, approximately 1 / 4λ with respect to the wavelength λ of the surface acoustic wave. It has become.
[0016]
As the structure of the IDTs 54a to 60a, for example, the structure of the IDTs 57a to 60a of the surface acoustic wave electrodes 57 to 60 of the parallel resonator group is the electrode finger A1 and electrodes intersecting with the electrode finger A1, as shown in FIGS. The fingers A2 are arranged so as to cross each other, and are aligned perpendicular to the propagation direction of the generated surface acoustic wave. For example, the electrode width Pw of the electrode fingers A1 and A2 and the electrode fingers A1, A2 The electrode finger intervals Pp are set to substantially the same length. In this embodiment, the electrode width Pw and the electrode finger interval Pp are set to be substantially the same, but the length is not necessarily limited to this, and the electrode width Pw and the electrode finger interval Pp are made different. However, the same effect of the present invention can be obtained.
[0017]
61 is an input terminal, and 62 is an output terminal. IDTs 54 a to 56 a are connected in series from the input terminal 61 and connected to the output terminal 62. One side of the IDTs 57a to 60a is connected to each of these through the reflectors 57b, 58c, 59c, 60b, and the other side is connected to each ground electrode (GND) by the reflectors 57c, 58b, 59b, 60c.
[0018]
Here, in the present invention, as shown in FIG. 3, among the surface acoustic wave electrodes 57 to 60 of the parallel resonator group, the surface acoustic wave electrode 60 has a Q value degradation structure that degrades the obtained Q value. Yes. Further, in addition to the Q value degradation structure, the resonance frequency Fr of the surface acoustic wave electrode 60 is lower than the anti-resonance frequency Fa of the surface acoustic wave electrodes 57 to 59 of the parallel resonator group, and the surface acoustic wave electrodes 57 to 59 It was made higher than the resonance frequency Fr.
[0019]
Here, the Q value is generally expressed as Q = 2πFL / R (F: resonance frequency L: inductance R: resonance resistance). In the present invention, the resonance frequency Fr of the surface acoustic wave electrode 60 is equal to the passband of the filter. It is found that the left shoulder of the pass band is made steep by reducing the Q value obtained by the surface acoustic wave electrode 60.
[0020]
The degree of deterioration of the Q value is such that the impedance at the resonance frequency Fr of the surface acoustic wave electrode 60 approaches the locus connected by the resonance frequency Fr and the antiresonance frequency Fa in the resonance characteristics of the surface acoustic wave electrodes 57 to 59. It is better to degrade the insertion loss of the resonance characteristics.
[0021]
The Q value deterioration structure may be formed so as to increase the resonance resistance R. In order to increase the Q resistance deterioration structure, the following specific configuration is preferable.
Specifically, the resonance resistance R is increased and the Q value is reduced by reducing the logarithm of each electrode finger A1, A2 of the surface acoustic wave electrode 60 compared to the logarithm of each electrode finger A1, A2 of the surface acoustic wave electrodes 57-59. Can be deteriorated.
Further, the length Px where the electrode fingers A1 and A2 of the surface acoustic wave electrode 60 cross each other is made shorter than the length Px where the electrode fingers of the other surface acoustic wave electrodes 57 to 59 cross each other. The resistance R can be increased to degrade the Q value.
[0022]
Further, as shown in FIG. 4, the surface acoustic wave electrode 601 is composed of sub-electrodes 61 and 62 formed of comb-like electrodes, and the sub-electrodes 61 and 62 are connected in series with each other. One of the sub-electrodes 61 made of comb-like electrodes is an electrode 61a connected to a line connecting the input terminal (IN) and the output terminal (OUT), an electrode 61b facing the electrode 61a, and a sub-electrode connected to the electrode 61a. One electrode 62a of the electrode 62 and an electrode 62b connected to the ground side facing the electrode 62a are connected in series. Because of this series connection, the resonance resistance R becomes higher than that of the surface acoustic wave electrode 60 of FIG. 1, and the Q value can be deteriorated.
[0023]
On the other hand, the resonance frequency Fr formed by the surface acoustic wave electrode 60 is lower than the anti-resonance frequency Fa formed by the surface acoustic wave electrodes 57 to 59 of the other parallel resonator groups, and the surface acoustic waves of the other parallel resonator groups. As means for raising the resonance frequency Fr formed by the electrodes 57 to 59, as shown in FIG. 2, the width Pw of the electrode fingers of the surface acoustic wave electrodes 57 to 60 of the parallel resonator group and each electrode finger The electrode finger pitch formed by the electrode finger spacing Pp may be formed so that the surface acoustic wave electrodes 57 to 59 other than the surface acoustic wave electrode 60 are longer. In this case, the electrode finger pitch is changed by making the electrode finger widths Pw of the surface acoustic wave electrodes 57 to 60 of the parallel resonator group substantially the same and changing the electrode finger interval Pp between the electrode fingers, The electrode finger spacing Pp between the electrode fingers is made substantially the same, the width Pw of each electrode finger is changed, the width Pw of each electrode finger of the surface acoustic wave electrodes 57-60 of the parallel resonator group is changed, and each electrode finger There is a method of changing the electrode finger interval Pp between each other.
[0024]
Further, the metallization ratio of the surface acoustic wave electrodes 57 to 59 of other parallel resonator groups is larger than the metallization ratio of the surface acoustic wave electrode 60 (the ratio of the electrode finger width Pw to the electrode finger pitch; hereinafter the same). There is a method of forming so as to be. For example, for the surface acoustic wave electrodes 57 to 59 shown in FIG. 2A, the electrode finger widths of the electrode fingers A1 and A2 are set to Pw = 0.500 μm and the electrode finger interval Pp = 0.500 μm, and FIG. With respect to the surface acoustic wave electrode 60 shown, the resonance frequency obtained can be made different by setting the electrode finger width to Pw = 0.400 μm and the electrode finger interval Pp = 0.600 μm.
[0025]
As another method, the electrode thickness of the surface acoustic wave electrode 60 may be made thinner than the electrode thicknesses of the surface acoustic wave electrodes 57 to 59 of other parallel resonator groups.
[0026]
In the above description, one surface acoustic wave electrode 60 of the parallel resonator group forms a pole on the higher frequency side than the attenuation pole formed by the other surface acoustic wave electrodes 57 to 59 of the parallel resonator group. However, the present invention is not limited to this, and two or more surface acoustic wave electrodes of the parallel resonator group may be used. Even if it is such a structure, the same effect is acquired.
[0027]
Thus, according to the surface acoustic wave filter A of the present invention, conventionally, the attenuation poles of the surface acoustic wave electrodes 57 to 60 of the parallel resonator group have been used to form an attenuation pole on the lower side of the pass band. On the other hand, one surface acoustic wave electrode 60 of the parallel resonator group has a Q value deterioration structure, and its resonance frequency Fr is lower than the anti-resonance frequency Fa of the other surface acoustic wave electrodes 57 to 59, and Since the resonance frequency Fr of the other surface acoustic wave electrodes 57 to 59 is higher than that of the other surface acoustic wave electrodes 57, another new pole is formed in the filter characteristics from the low-frequency attenuation pole to the passband, As a result, it is possible to secure a sufficient shoulder characteristic by increasing the steepness of the low frequency side of the pass band while ensuring a wide pass band of the filter. In addition, since the passband attenuation characteristics hardly change, the conventional design method can be used as it is.
[0028]
Conventionally, the inductance value of the wire is changed by changing the wire length of the aluminum wire wire or the gold wire wire that are externally drawn electrodes, so that the attenuation amount in the low-frequency side is ensured. However, according to the present invention, the low-pass shoulder characteristics of the passband can be sharpened without using such a thing, so a stable yield can be obtained. Can also be secured.
[0029]
【Example】
Next, examples of the present invention will be shown to confirm the effects of the present invention.
Example 1
As the piezoelectric substrate 1, a 42 ° YX lithium tantalate substrate is used, and surface acoustic wave electrodes 54, 55, 56 of series resonators made of Al or Al alloy and surface acoustic wave electrodes 57 of parallel resonators are formed on the surface. 58, 59, and 60 were formed like the wiring of FIG. Thus, a ladder type SAW filter having a center frequency of 1.96 GHz was manufactured.
[0030]
In this case, the cross width Px of the surface acoustic wave electrodes 54, 55, and 56 of the series resonator is Px = 10 to 15λ, and the cross width Px of the surface acoustic wave electrodes 57, 58, and 59 of the parallel resonator is Px = 30λ. The cross width Px of the surface acoustic wave electrode 60 was Px = 20λ. In addition, the number of electrode pairs of the surface acoustic wave electrodes 54, 55 and 56 of the series resonator is 95 pairs, the number of electrode pairs of the surface acoustic wave electrodes 57, 58 and 59 of the parallel resonator is 45 pairs, and the number of electrode pairs of the surface acoustic wave electrode 60. 15 pairs.
Further, both the electrode finger width Pw and the electrode finger interval Pp of the surface acoustic wave electrodes 57, 58, 59 are set to Pp, Pw = 0.503 μm, and both the electrode finger width Pw and the electrode finger interval Pp of the surface acoustic wave electrode 60 are set. Pw, Pp = 0.500 μm, and the electrode finger pitch was made shorter than that of the surface acoustic wave electrodes 57-59. Note that both the electrode finger width Pw and the electrode finger interval Pp of the surface acoustic wave electrodes 54, 55 and 56 of the series resonator are Pp, Pw = 0.4845 μm, and the electrode width Pw and the electrode finger interval Pp are the same length. Is set.
[0031]
FIG. 5 shows the filter characteristics of the surface acoustic wave filter A thus formed. At this time, the vertical axis of FIG. 5 is the attenuation (5 dB / div), and the horizontal axis is the normalized frequency (center frequency f0: 1960 MHz, span: 196 MHz).
[0032]
In FIG. 5, attenuation poles by surface acoustic wave electrodes 57 to 59 of parallel resonators are formed in the vicinity of 0.97. Further, an attenuation pole is formed by surface acoustic wave electrodes 54, 55, and 56 of series resonators in the vicinity of 1.04.
[0033]
As shown in FIG. 5, the attenuation pole B by the surface acoustic wave electrode 60 of the parallel resonator is formed on the high frequency side of the pole on the low pass band side, so that the low band side shoulder characteristic becomes steep and the pass band It can be seen that the characteristics are wideband.
On the other hand, as a comparative example, the cross width Px of the surface acoustic wave electrodes 54, 55, and 56 of the series resonator is Px = 10 to 15λ, and the cross width Px of the surface acoustic wave electrodes 57 to 60 of the parallel resonator is any. Px = 30λ and the same length, and Pw and Pp of the surface acoustic wave electrodes 57 to 60 of the parallel resonator were Pw and Pp = 0.503 μm.
The number of electrode pairs of the surface acoustic wave electrodes 54, 55, and 56 of the series resonator is 95 pairs, the number of electrode pairs of the surface acoustic wave electrodes 57 to 60 of the parallel resonator is 45 pairs, and the electrode width Pw and the electrode finger interval Pp are set as follows. The surface acoustic wave filter of the comparative example set to the same length was formed, and the filter characteristics are shown in FIG. The vertical axis in FIG. 6 is also the attenuation (5 dB / div), and the horizontal axis is the normalized frequency (center frequency f0: 1960 MHz, span: 196 MHz).
According to this filter characteristic, it can be seen that a filter that sufficiently satisfies the specifications of the low band side shoulder characteristic of the pass band cannot be obtained.
(Example 2)
Experiments were performed under the same conditions as in Example 1 except that the surface acoustic wave electrode 60 shown in FIG. 1 is the surface acoustic wave electrode 601 shown in FIG. 4 (the structure of the sub-electrodes 61 and 62 connected in series). In each of the sub-electrodes 61 and 62, the crossing width Px is Px = 20λ, both the electrode finger width Pw and the electrode finger interval Pp are Pp, and Pw = 0.5 μm. The number of electrode pairs is 45.
FIG. 7 shows the filter characteristics thus experimentally performed. Even in this result, the surface acoustic wave electrode 601 of the series resonator composed of the sub-electrodes 61 and 62 has an increased resonance resistance as compared with the surface acoustic wave electrode 60 shown in FIG. Compared to the Q values of the surface acoustic wave electrodes 57 to 59 of other parallel resonator groups, the resonance frequency of the surface acoustic wave electrode 60 is lower than the anti-resonance frequency of the surface acoustic wave electrodes 57 to 59. In addition, since the resonance frequency of the surface acoustic wave electrodes 57 to 59 is higher than that of the surface acoustic wave electrode, it is understood that a new attenuation pole is generated on the left shoulder of the pass band, and the steepness on the lower side of the pass band is increased. it can.
[0034]
【The invention's effect】
According to the configuration of the present invention, some surface acoustic wave electrodes have a Q value degradation structure, the resonance frequency thereof is lower than the anti-resonance frequency of other surface acoustic wave electrodes, and the resonance of other surface acoustic wave electrodes. Since the frequency is higher than the frequency, a new attenuation pole is formed in the filter characteristics from the low-frequency side attenuation pole until it enters the passband, thereby ensuring a wide passband for the filter and reducing the passband. It is possible to provide a surface acoustic wave filter in which the steepness on the region side becomes large and sufficient shoulder characteristics can be secured.
[Brief description of the drawings]
FIG. 1 is a plan view of a surface acoustic wave filter according to the present invention.
2A is a diagram illustrating surface acoustic wave electrodes 57 to 59, and FIG. 2B is a diagram illustrating a configuration of a surface acoustic wave electrode 60. FIG.
FIG. 3 is a diagram showing resonance characteristics of the surface acoustic wave electrodes 57 to 59 and the surface acoustic wave electrode 60 of the present invention.
FIG. 4 is a circuit diagram illustrating another surface acoustic wave filter of the present invention.
FIG. 5 is a characteristic diagram showing filter characteristics of the present invention.
FIG. 6 is a characteristic diagram showing filter characteristics of a comparative example.
FIG. 7 is a characteristic diagram showing filter characteristics in another surface acoustic wave filter of the present invention.
FIG. 8 is a schematic plan view for explaining a conventional surface acoustic wave filter.
FIG. 9 is an enlarged plan view for explaining a 1-port surface acoustic wave electrode.
[Explanation of symbols]
A: surface acoustic wave filter 1: piezoelectric substrates 54 to 56: surface acoustic wave electrodes 57-60 of a series resonator: surface acoustic wave electrodes 61 of a parallel resonator 61: input terminal 62: output terminal

Claims

A series resonator group in which a plurality of surface acoustic wave electrodes are connected in series between an input terminal and an output terminal on the surface of the piezoelectric substrate, and an input terminal side or an output terminal side of each surface acoustic wave electrode of the series resonator group A parallel resonator group in which a plurality of surface acoustic wave electrodes are connected in parallel is arranged between the ground and the ground, and the resonance frequency formed by the surface acoustic wave electrodes of the series resonator group and the elasticity of the parallel resonator group In the surface acoustic wave filter that forms the passband of the filter by substantially matching the anti-resonance frequency formed by the surface wave electrode,
Among the surface acoustic wave electrodes of the group of parallel resonators, some of the surface acoustic wave electrodes have a Q value deterioration structure in which the obtained Q value is deteriorated more than the Q value obtained by other surface acoustic wave electrodes. The resonance frequency formed by the partial surface acoustic wave electrodes is lower than the anti-resonance frequency formed by the surface acoustic wave electrodes of the other parallel resonator groups, and is formed by the surface acoustic wave electrodes of the other parallel resonator groups. A surface acoustic wave filter characterized by having a resonance frequency higher than the resonance frequency.

The surface acoustic wave electrode is composed of comb-like electrodes arranged so that the electrode fingers cross each other, and the electrode finger is composed of the electrode finger width of the surface acoustic wave electrode and the electrode finger interval between the electrode fingers. By forming the pitch so that the other surface acoustic wave electrodes of the parallel resonator group are longer than the part of the surface acoustic wave electrodes, the resonance frequency formed by the part of the surface acoustic wave electrodes can be different. 2. The resonance frequency formed by a surface acoustic wave electrode of another parallel resonator group and lower than an anti-resonance frequency formed by a surface acoustic wave electrode of another parallel resonator group. Surface acoustic wave filter.

The surface acoustic wave electrode is composed of comb-like electrodes arranged so that the electrode fingers cross each other, and is composed of the electrode finger width of the surface acoustic wave electrode and the electrode finger spacing between the electrode fingers. By forming the ratio of the width of the electrode finger to the pitch so that the other surface acoustic wave electrodes of the parallel resonator group are larger than the part of the surface acoustic wave electrodes, the part of the surface acoustic wave electrodes The resonance frequency formed by the above is lower than the anti-resonance frequency formed by the surface acoustic wave electrodes of the other parallel resonator groups and higher than the resonance frequency formed by the surface acoustic wave electrodes of the other parallel resonator groups. The surface acoustic wave filter according to claim 1.

The surface acoustic wave electrode is composed of comb-like electrodes arranged so that electrode fingers cross each other, and the thickness of the surface acoustic wave electrode of the part is set to the surface acoustic wave electrode of another parallel resonator group The resonance frequency formed by the partial surface acoustic wave electrodes is lower than the anti-resonance frequency formed by the surface acoustic wave electrodes of the other parallel resonator groups, and 2. The surface acoustic wave filter according to claim 1, wherein the surface acoustic wave filter is higher than a resonance frequency formed by the surface acoustic wave electrodes of the parallel resonator group.

As the Q value deterioration structure, the surface acoustic wave electrode is composed of comb-like electrodes arranged so that the electrode fingers cross each other, and the logarithm of each electrode finger of the part of the surface acoustic wave electrodes is different from each other. 2. The surface acoustic wave filter according to claim 1, wherein the number of surface acoustic wave electrodes of the parallel resonator group is less than the number of pairs of electrode fingers.

As the Q value deterioration structure, the surface acoustic wave electrode is composed of comb-like electrodes arranged so that the electrode fingers cross each other, and the electrode fingers of the partial surface acoustic wave electrodes cross each other. 2. The surface acoustic wave filter according to claim 1, wherein the length of the surface acoustic wave filter is shorter than the length of crossing of the electrode fingers of the surface acoustic wave electrodes of the other parallel resonator groups.

As the Q value deterioration structure, the surface acoustic wave electrode is composed of comb-like electrodes arranged so that electrode fingers cross each other, and the partial surface acoustic wave electrode is formed from the comb-like electrode 2. The surface acoustic wave filter according to claim 1, comprising a plurality of sub electrodes connected in series.