JPH11205072A - Weighting electrode for surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a weighing electrode with few deteriorations in an amplitude characteristic by means of a surface acoustic wave diffraction effect, even when a same weighting coefficient is repeatedly used twice in weighing coefficient data of a λ(surface acoustic wave length)/4-interval sampling. SOLUTION: Intersecting parts are provided in two electrode fingers 11 and 14 by λ/2-interval and a floating electrode 15 is provided in a part corresponding to the intersecting parts at a position at equal distance from the centers of the two electrode fingers. The size of surface acoustic wave excited in the intersecting parts which are constituted by the both adjacent electrode fingers 11 and 14 and the float electrode 15 is equal and arbitrary weighing coefficient where the same weighting coefficient is repeated twice by λ/4-interval sampling can be expressed. Also the intersecting parts of the both adjacent electrode fingers 11 and 14 and the float electrode 15 are the same in positions in a direction being vertical with respect to a surface acoustic wave propagating direction so that the width of the intersecting part corresponding to the max. weighting coefficient is made to be provided with opening length W. The width of the other intersecting part is widened so that the deterioration of the filter characteristic by the diffraction effect is reduced.

Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION

【０００１】[0001]

【発明の属する技術分野】本発明は、弾性表面波フィル
タに係り、特に弾性表面波フィルタの重み付け電極に関
する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter, and more particularly, to a weighting electrode of a surface acoustic wave filter.

【０００２】[0002]

【従来の技術】従来の弾性表面波フィルタに用いる重み
付け電極としては、図３に示すような交叉幅を、場所に
より重み付け関数に比例して変化させるアポダイズド電
極が主に用いられている。図において、４１、４２はバ
ス電極、３１〜３４、３６、３７は電極指、Ｗは開口
長、ｗ１、ｗ２は交叉長、λは弾性表面波の波長を示
す。この種の電極の例は、特開昭６０−２６４１１０号
公報、特開平５−６３４８８号公報、特開平７−１０６
９０８号公報、特開平６−２９７７１号公報、特開平３
−１０８８０８号公報等に示されている。2. Description of the Related Art As a weighting electrode used in a conventional surface acoustic wave filter, an apodized electrode whose crossing width as shown in FIG. 3 is changed in proportion to a weighting function depending on a location is mainly used. In the figure, 41 and 42 are bus electrodes, 31 to 34, 36 and 37 are electrode fingers, W is an opening length, w1 and w2 are cross lengths, and λ is a wavelength of a surface acoustic wave. Examples of this type of electrode are disclosed in JP-A-60-264110, JP-A-5-63488, and JP-A-7-106.
908, JP-A-6-29771 and JP-A-3
-108808.

【０００３】[0003]

【発明が解決しようとする課題】図３に示す従来のアポ
ダイズド電極では、λ／４間隔サンプリングの重み付け
係数データで、同一の重み付け係数が２回ずつ繰り返し
て用いられている。この場合、最大重み付け係数が同符
号で連続して２回用いられているため、最大重み付け係
数に対応する交叉幅はアポダイズド電極の開口長Ｗの約
１／２となり、その他の重み付け係数が対応する交叉幅
も狭くなるため、弾性表面波の回折効果による弾性表面
波フィルタの振幅特性の劣化が大きくなるという欠点が
あった。In the conventional apodized electrode shown in FIG. 3, the same weighting coefficient is repeatedly used twice for weighting coefficient data of λ / 4 interval sampling. In this case, since the maximum weighting coefficient is used twice in succession with the same sign, the cross width corresponding to the maximum weighting coefficient is about の of the opening length W of the apodized electrode, and the other weighting coefficients correspond. Since the cross width is also narrow, there is a disadvantage that the amplitude characteristic of the surface acoustic wave filter is greatly deteriorated due to the diffraction effect of the surface acoustic wave.

【０００４】本発明は、上記事情を考慮し、λ／４間隔
サンプリングの重み付け係数データで、同一の重み付け
係数が２回繰り返して用いられる場合においても、弾性
表面波の回折効果による振幅特性の劣化の少ない弾性表
面波フィルタ用重み付け電極を提供することを目的とす
る。The present invention has been made in consideration of the above circumstances, and in the case where the same weighting coefficient is used twice repeatedly with the weighting coefficient data of λ / 4 interval sampling, the deterioration of the amplitude characteristic due to the diffraction effect of the surface acoustic wave. It is an object of the present invention to provide a weighting electrode for a surface acoustic wave filter having a small number of components.

【０００５】[0005]

【課題を解決するための手段】請求項１の発明の弾性表
面波フィルタ用重み付け電極は、圧電基板上の交叉指状
電極で構成された弾性表面波フィルタ用重み付け電極に
おいて、λ／２間隔で互いに隣り合い、且つ、バス電極
に接続された複数の電極指を有すると共に、これら互い
に隣り合う各複数の電極指相互間に、一方側に隣接する
電極指と他方側に隣接する電極指とから等距離の位置
で、且つ、一方側に隣接する電極指と他方側に隣接する
電極指の交叉部に対応する位置に、浮き電極を設けたこ
とを特徴とする。請求項２の発明は、請求項１におい
て、前記浮き電極は、前記電極指を含む平面と同一の平
面に含まれることを特徴とする。請求項３の発明は、請
求項１または２において、前記浮き電極は、前記平面内
で前記電極指との間に間隔をおいて設けられたことを特
徴とする。According to a first aspect of the present invention, there is provided a weighting electrode for a surface acoustic wave filter, wherein the weighting electrode for a surface acoustic wave filter is composed of interdigital electrodes on a piezoelectric substrate. Adjacent to each other, and having a plurality of electrode fingers connected to the bus electrode, between each of the plurality of electrode fingers adjacent to each other, from the electrode finger adjacent to one side and the electrode finger adjacent to the other side. Floating electrodes are provided at equidistant positions and at positions corresponding to intersections of electrode fingers adjacent to one side and electrode fingers adjacent to the other side. According to a second aspect of the present invention, in the first aspect, the floating electrode is included in the same plane as a plane including the electrode fingers. According to a third aspect of the present invention, in the first or second aspect, the floating electrode is provided at a distance from the electrode finger in the plane.

【０００６】[0006]

【発明の実施の形態】以下、本発明の実施の形態を図面
に基づいて説明する。図１は実施形態の弾性表面波フィ
ルタ用重み付け電極の平面図である。この弾性表面波フ
ィルタ用重み付け電極は、λ／２間隔で互いに隣り合う
複数の電極指１１〜１４を有すると共に、これら各電極
指１１〜１４の相互間に配された浮き電極１５を有す
る。電極指１１及び電極指１３はバス電極２１と、電極
指１２及び電極指１４はバス電極２２と各々接続されて
いる。Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of a weighting electrode for a surface acoustic wave filter according to an embodiment. The surface acoustic wave filter weighting electrode has a plurality of electrode fingers 11 to 14 adjacent to each other at an interval of λ / 2, and has a floating electrode 15 disposed between the electrode fingers 11 to 14. The electrode fingers 11 and 13 are connected to the bus electrode 21, and the electrode fingers 12 and 14 are connected to the bus electrode 22.

【０００７】また、浮き電極１５は、左隣の電極指１
１，１２と右隣の電極指１３，１４とから等距離の位置
で、且つ、左隣の電極指１１と右隣の電極指１４の交叉
部に対応する位置に設けられている。なお、電極指１
６、１７はダミー電極指であり、一方のダミー電極指１
６は一方のバス電極２１と接続され、他方のダミー電極
指１７は他方のバス電極２２と接続されている。The floating electrode 15 is connected to the electrode finger 1 on the left.
They are provided at positions equidistant from the electrode fingers 1 and 12 and the right electrode fingers 13 and 14 and at positions corresponding to the intersections of the left electrode finger 11 and the right electrode finger 14. The electrode finger 1
Reference numerals 6 and 17 denote dummy electrode fingers.
6 is connected to one bus electrode 21, and the other dummy electrode finger 17 is connected to the other bus electrode 22.

【０００８】次に作用について、図１及び図２を参照し
て説明する。弾性表面波は交叉部を有する２本の電極指
間に電圧が印可されることによって励振され、その大き
さは交叉部の静電容量に比例し、印可される電圧にも比
例する。したがって、励振される弾性表面波の大きさ
は、交叉部に蓄積される電荷量に比例することになる。
また、励振される弾性表面波の極性は、印可された電圧
による電界の方向で決定される。Next, the operation will be described with reference to FIGS. The surface acoustic wave is excited by applying a voltage between two electrode fingers having a crossing, and its magnitude is proportional to the capacitance of the crossing and is also proportional to the applied voltage. Therefore, the magnitude of the surface acoustic wave to be excited is proportional to the amount of charge stored in the intersection.
The polarity of the surface acoustic wave to be excited is determined by the direction of the electric field due to the applied voltage.

【０００９】電極指１１と浮き電極１５は幅ｗ１の交叉
部を有しており、同様に、浮き電極１５と電極指１４は
幅ｗ２の交叉部を有しており、これらの交叉部の幅は等
しく設定されている。また、浮き電極１５は電極指１１
と電極指１４とから等距離に配置されている。したがっ
て、これらの交叉部の静電容量は等しくなる。The electrode finger 11 and the floating electrode 15 have an intersection having a width w1. Similarly, the floating electrode 15 and the electrode finger 14 have an intersection having a width w2. Are set equal. In addition, the floating electrode 15 is
And the electrode finger 14 at the same distance. Therefore, the capacitance of these intersections becomes equal.

【００１０】バス電極２１とバス電極２２との間、すな
わち、電極指１１と電極指１４との間に電圧が印可され
ると、これらの交叉部の静電容量は等しいことから、こ
れらの交叉部に蓄積される電荷量は等しくなる。また、
これらの交叉部の電界の方向は同方向であるから、電極
指１１と浮き電極１５とにより励振される弾性表面波の
大きさｋ１と、浮き電極１５と電極指１４とにより励振
される弾性表面波の大きさｋ２は等しくなる。そして、
他のタップ以降で励振される弾性表面波の大きさも同様
となり、各タップで励振される弾性表面波の大きさ、す
なわち、各タップの重み付け係数ｋ１、ｋ２、ｋ３、ｋ
４は図２のようになる。When a voltage is applied between the bus electrode 21 and the bus electrode 22, that is, between the electrode finger 11 and the electrode finger 14, since the capacitance of these intersections is equal, these intersections are formed. The amounts of charges stored in the sections become equal. Also,
Since the direction of the electric field at these intersections is the same, the magnitude k1 of the surface acoustic wave excited by the electrode finger 11 and the floating electrode 15 and the elastic surface wave excited by the floating electrode 15 and the electrode finger 14 The wave magnitudes k2 are equal. And
The same applies to the magnitude of the surface acoustic wave excited after the other taps, and the magnitude of the surface acoustic wave excited at each tap, that is, the weighting coefficient k1, k2, k3, k of each tap.
4 is as shown in FIG.

【００１１】したがって、λ／４間隔サンプリングで２
回同じ重み付け係数が繰り返された、任意の重み付け係
数を表現することが可能となる。また、浮き電極１５と
その両隣の電極指１１、１４により構成される各交叉部
は、弾性表面波の伝播方向に垂直な方向における位置が
同一であるため、最大重み付け係数に対応する交叉部の
幅を開口長Ｗとすることができ、他の交叉部の幅も広く
することができることから、回折効果によるフィルタ特
性の劣化を低減することができる。[0011] Therefore, when sampling at λ / 4 interval, 2
It is possible to express an arbitrary weighting coefficient in which the same weighting coefficient is repeated twice. Further, since each of the intersections formed by the floating electrode 15 and the electrode fingers 11 and 14 on both sides thereof has the same position in the direction perpendicular to the propagation direction of the surface acoustic wave, the intersection of the intersection corresponding to the maximum weighting coefficient is used. Since the width can be set to the opening length W and the width of the other intersections can be increased, the deterioration of the filter characteristics due to the diffraction effect can be reduced.

【００１２】[0012]

【発明の効果】以上説明したように、本発明によれば、
浮き電極とその両隣の電極指により構成される両交叉部
の位置が、弾性表面波の伝播方向に垂直な方向において
同一となるため、最大重み付け係数に対応する交叉部の
幅を開口長Ｗと同一にすることができ、他の交叉部の幅
も広くすることができ、それにより、従来のアポダイズ
ド電極で生じていたような回折効果によるフィルタ特性
の劣化を低減することができる。As described above, according to the present invention,
Since the positions of the intersections formed by the floating electrode and the electrode fingers on both sides thereof are the same in the direction perpendicular to the propagation direction of the surface acoustic wave, the width of the intersection corresponding to the maximum weighting coefficient is defined as the opening length W. The width can be made the same, and the width of the other crossing portions can be widened, whereby the deterioration of the filter characteristics due to the diffraction effect, which occurs in the conventional apodized electrode, can be reduced.

【図面の簡単な説明】[Brief description of the drawings]

【図１】本発明の弾性表面波フィルタ用重み付け電極の
一実施の形態を示す平面図である。FIG. 1 is a plan view showing one embodiment of a weighting electrode for a surface acoustic wave filter according to the present invention.

【図２】本発明の弾性表面波フィルタ用重み付け電極の
一実施の形態の重み付け係数を示す説明図である。FIG. 2 is an explanatory diagram showing weighting coefficients of one embodiment of a weighting electrode for a surface acoustic wave filter according to the present invention.

【図３】従来例のアポダイズド電極を示す平面図であ
る。FIG. 3 is a plan view showing a conventional apodized electrode.

【符号の説明】[Explanation of symbols]

λ…弾性表面波の波長 １１〜１４，１６，１７，３１〜３４，３６，３７…電
極指 １５…浮き電極 ２１〜２２，４１〜４２…バス電極 Ｗ…開口長 ｗ１，ｗ２…交叉幅 ｋ１，ｋ２，ｋ３，ｋ４…重み付け係数λ: wavelength of surface acoustic wave 11 to 14, 16, 17, 31 to 34, 36, 37: electrode finger 15: floating electrode 21 to 22, 41 to 42: bus electrode W: opening length w1, w2: cross width k1 , K2, k3, k4 ... weighting factors

Claims (3)

【特許請求の範囲】[Claims] 【請求項１】 圧電基板上の交叉指状電極で構成された
弾性表面波フィルタ用重み付け電極において、 弾性表面波の波長をλとした場合、λ／２間隔で互いに
隣り合い、且つ、バス電極に接続された複数の電極指を
有すると共に、これら互いに隣り合う各複数の電極指相
互間に、一方側に隣接する電極指と他方側に隣接する電
極指とから等距離の位置で、且つ、一方側に隣接する電
極指と他方側に隣接する電極指の交叉部に対応する位置
に、浮き電極を設けたことを特徴とする弾性表面波フィ
ルタ用重み付け電極。1. A weighting electrode for a surface acoustic wave filter comprising interdigital electrodes on a piezoelectric substrate, wherein, when the wavelength of the surface acoustic wave is λ, they are adjacent to each other at an interval of λ / 2, and a bus electrode. Having a plurality of electrode fingers connected to each other, between each of the plurality of electrode fingers adjacent to each other, at a position equidistant from the electrode finger adjacent to one side and the electrode finger adjacent to the other side, and A weighting electrode for a surface acoustic wave filter, wherein a floating electrode is provided at a position corresponding to an intersection of an electrode finger adjacent to one side and an electrode finger adjacent to the other side. 【請求項２】 前記浮き電極は、前記電極指を含む平面
と同一の平面に含まれることを特徴とする請求項１記載
の弾性表面波フィルタ用重み付け電極。2. The weighting electrode for a surface acoustic wave filter according to claim 1, wherein the floating electrode is included in the same plane as a plane including the electrode fingers. 【請求項３】 前記浮き電極は、前記平面内で前記電極
指との間に間隔をおいて設けられたことを特徴とする請
求項１または２に記載の弾性表面波フィルタ用重み付け
電極。3. The weighting electrode for a surface acoustic wave filter according to claim 1, wherein the floating electrode is provided at a distance from the electrode finger in the plane.