JP2915735B2 - Surface acoustic wave filter device - Google Patents
Surface acoustic wave filter deviceInfo
- Publication number
- JP2915735B2 JP2915735B2 JP5041220A JP4122093A JP2915735B2 JP 2915735 B2 JP2915735 B2 JP 2915735B2 JP 5041220 A JP5041220 A JP 5041220A JP 4122093 A JP4122093 A JP 4122093A JP 2915735 B2 JP2915735 B2 JP 2915735B2
- Authority
- JP
- Japan
- Prior art keywords
- electrode
- acoustic wave
- surface acoustic
- wave filter
- converter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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- Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
Description
【０００１】[0001]
【産業上の利用分野】本発明は弾性表面波フィルタ装
置、特に小型化及び帯域外減衰量の改善を図った弾性表
面波フィルタ装置に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter device, and more particularly to a surface acoustic wave filter device which is reduced in size and has improved attenuation outside a band.
【０００２】[0002]
【従来の技術】圧電性基板上にインタディジタル型の入
力側変換器及び出力側変換器を形成して特定の周波数帯
域の信号を取り出す弾性表面波フィルタ装置が実用化さ
れている。この弾性表面波フィルタ装置では、挿入損失
をできるだけ小さくするため入力側及び出力側変換器と
して一方向性トランスジューサが用いられている。2. Description of the Related Art A surface acoustic wave filter device has been put into practical use in which an interdigital input-side converter and an output-side converter are formed on a piezoelectric substrate to extract a signal in a specific frequency band. In this surface acoustic wave filter device, a unidirectional transducer is used as an input-side and output-side converter in order to minimize insertion loss.
【０００３】このような一方向性トランスジューサとし
て、例えば特公平３−20929 号公報に記載されている一
方向性トランスジューサが既知である。この既知の一方
向性トランスジューサは圧電性基板として大きな電気機
械結合係数を有するLiNbO3単結晶体が用いられ、このLi
NbO3基板上にインタディジタル型の正電極及び負電極が
形成されている。正電極及び負電極の電極指（弾性表面
波の進行方向に見て互いに重り合う部分）は互いにλ／
２（λは基本弾性表面波の波長）の中心間距離を以て形
成され、これら正電極と負電極との間に電気的にフロー
ティング状態にある浮き電極が形成されている。正及び
負電極並びに浮き電極の電極指の弾性表面波の伝播方向
の幅はλ／８に設定され、浮き電極と正及び負電極との
間の中心間距離ｄは、λ／８＜ｄ＜λ／４に設定されて
いる。As such a one-way transducer, for example, a one-way transducer described in Japanese Patent Publication No. 3-20929 is known. This known unidirectional transducers LiNbO 3 single crystal having a large electromechanical coupling coefficient as the piezoelectric substrate is used, the Li
An interdigital positive electrode and a negative electrode are formed on an NbO 3 substrate. The electrode fingers of the positive electrode and the negative electrode (portions overlapping each other when viewed in the traveling direction of the surface acoustic wave) are λ /
2 (λ is the wavelength of the basic surface acoustic wave), and a floating electrode in an electrically floating state is formed between the positive electrode and the negative electrode. The width of the positive and negative electrodes and the floating electrode in the propagation direction of the surface acoustic wave of the electrode finger is set to λ / 8, and the center-to-center distance d between the floating electrode and the positive and negative electrodes is λ / 8 <d < λ / 4 is set.
【０００４】別の弾性表面波フィルタ装置として、特開
平３−133209号公報に記載されているＳＡＷフィルタが
既知である。この既知のＳＡＷフィルタは広帯域用のフ
ィルタ装置として構成され、圧電性基板として同様にLi
NbO3が用いられている。そして、LiNbO3基板上に正電極
及び負電極が形成され、これら正電極と負電極との間に
開放型の浮き電極及び短絡型の浮き電極の両方が形成さ
れている。そして、各電極の電極指の幅はλ／12に設定
され、正電極と負電極との間にλ／６のピッチで開放型
及び短絡型の浮き電極が形成されている。As another surface acoustic wave filter device, a SAW filter described in Japanese Patent Application Laid-Open No. 3-133209 is known. This known SAW filter is configured as a filter device for a wide band, and is similarly made of Li as a piezoelectric substrate.
NbO 3 is used. A positive electrode and a negative electrode are formed on the LiNbO 3 substrate, and both an open floating electrode and a short-circuit floating electrode are formed between the positive electrode and the negative electrode. The width of the electrode finger of each electrode is set to λ / 12, and open and short-type floating electrodes are formed between the positive electrode and the negative electrode at a pitch of λ / 6.
【０００５】[0005]
【発明が解決しようとする課題】上述した弾性表面波フ
ィルタ装置は挿入損失が比較的小さく、しかも位相特性
及び周波数特性を適切に制御できるため高い有用性を有
している。一方、ディジタル通信システムの開発に伴な
い狭帯域特性を有し温度特性に優れたの弾性表面波フィ
ルタ装置の開発が強く要請されている。狭帯域特性のフ
ィルタ装置には温度変化に対する通過帯域の変化が小さ
く安定な通過帯域特性が要求される。すなわち、広帯域
特性のフィルタ装置の場合、通過帯域幅自体が広いた
め、温度変化によって通過帯域が変化しても帯域幅全体
に対する通過帯域の変化量の割合が小さいため大きな問
題とはならなかった。これに対して、狭帯域フィルタ装
置においては、通過帯域幅自体が狭いため、設定した通
過帯域幅に対する通過帯域幅変化量の割合が大きくわず
かな温度変化により設定した中心周波数が通過帯域外と
なるおそれがあった。従って、ディジタル通信用の狭帯
域フィルタ装置においては、温度変化に対して安定な通
過帯域特性を有することが極めて重要である。The above-described surface acoustic wave filter device has high utility since the insertion loss is relatively small and the phase characteristics and frequency characteristics can be appropriately controlled. On the other hand, with the development of digital communication systems, there is a strong demand for the development of a surface acoustic wave filter device having narrow band characteristics and excellent temperature characteristics. A filter device having a narrow band characteristic is required to have a stable pass band characteristic in which a change in the pass band with respect to a temperature change is small. That is, in the case of a filter device having a wide band characteristic, since the pass band width itself is wide, even if the pass band changes due to a temperature change, the ratio of the change amount of the pass band to the entire bandwidth is small, so that there is no significant problem. On the other hand, in the narrow band filter device, since the pass band width itself is narrow, the ratio of the amount of change in the pass band width to the set pass band is large, and the center frequency set by a slight temperature change is outside the pass band. There was a fear. Therefore, it is very important for a narrow band filter device for digital communication to have a stable pass band characteristic with respect to a temperature change.
【０００６】一方、前述したLiNbO3基板上に一方向性ト
ランスジューサを形成した弾性表面波フィルタ装置は、
LiNbO3基板の電気機械結合係数が大きいため挿入損失を
低く押えることができるが、温度変化に対する通過帯域
の変化量が大きく、従って従来の弾性表面波フィルタ装
置をそのまま狭帯域フィルタ装置に適用したので、温度
変化に起因する帯域変動の観点より実用化できないのが
実情である。On the other hand, a surface acoustic wave filter device in which a unidirectional transducer is formed on a LiNbO 3 substrate as described above,
The insertion loss can be kept low because the electromechanical coupling coefficient of the LiNbO 3 substrate is large, but the amount of change in the pass band with respect to temperature change is large, and therefore the conventional surface acoustic wave filter device was applied to the narrow band filter device as it was. In fact, it cannot be practically used from the viewpoint of band fluctuation due to temperature change.
【０００７】さらに、一方向性トランスジューサは電極
の対数が多いため縦長の形態になってしまう。特に、フ
ィルタ装置の通過帯域幅は送信側及び受信側変換器の電
極対数に依存するため、狭帯域フィルタ装置を構成する
場合変換器の電極対数が増大し、フィルタ装置の形態と
して一方向において特に長くなりすぎてしまう。この結
果、フィルタ装置を回路基板に装着した場合、実質的に
大きな面積を占有する不具合が生じてしまう。さらに、
従来の一方向性トランスジューサを用いたフィルタ装置
は、挿入損失は比較的小さいものの帯域外減衰量が不充
分であり、帯域外減衰量を一層抑制した一方向性トラン
スジューサの開発が強く要請されている。[0007] Further, the unidirectional transducer has a vertically long shape because of a large number of electrodes. In particular, since the pass bandwidth of the filter device depends on the number of electrode pairs of the transmitter and the converter on the receiving side, when configuring a narrow band filter device, the number of electrode pairs of the converter increases, and the form of the filter device is particularly one-way. It will be too long. As a result, when the filter device is mounted on a circuit board, there occurs a problem that the filter device occupies a substantially large area. further,
A conventional filter device using a one-way transducer has a relatively small insertion loss but an insufficient amount of out-of-band attenuation, and there is a strong demand for the development of a one-way transducer that further suppresses the out-of-band attenuation. .
【０００８】従って、本発明の目的は上述した欠点を除
去し、送信側及び受信側変換器の対数が増大しても、実
質的な占有面積が少なくなると共に帯域外減衰量が一層
抑制された弾性表面波フィルタ装置を提供することにあ
る。Accordingly, an object of the present invention is to eliminate the above-mentioned disadvantages, and even if the logarithms of the transmitter and the receiver are increased, the occupied area is substantially reduced and the out-of-band attenuation is further suppressed. An object of the present invention is to provide a surface acoustic wave filter device.
【０００９】[0009]
【課題を解決するための手段】本発明による弾性表面波
フィルタ装置は、水晶基板上に形成した送信側変換器及
び受信側変換器を有するＮ個（Ｎは２以上の整数）のト
ランスバーサル型の弾性表面波フィルタを具え、これら
弾性表面波フィルタを縦続接続した弾性表面波フィルタ
装置において、各弾性表面波フィルタの送信側変換器及
び受信側変換器が、正電極、負電極及び短絡型の浮き電
極のみをそれぞれ有し、基本弾性表面波の波長をλとし
た場合に、前記送信側変換器が、各電極指がλの中心間
距離を以って周期的に形成されている正電極と、各電極
指が、互いに隣接する正電極の電極指間の中間位置に周
期的に配置されている負電極と、各電極指が、互いに隣
接する正電極の電極指と負電極の電極指との間の中間位
置からλ／１２だけ弾性表面波の伝播方向の上流側に偏
位した位置にλのピッチで周期的に配置されている浮き
電極とを有し、前記受信側変換器が、各電極指がλの中
心間距離を以って周期的に形成されている正電極と、各
電極指が、互いに隣接する正電極の電極指間の中間位置
に配置されている負電極と、各電極指が、互いに隣接す
る正電極の電極指と負電極の電極指との間の中間位置か
らλ／１２だけ弾性表面波の伝播方向の下流側に偏位し
た位置にλのピッチで周期的に配置されている浮き電極
とを有し、前記送信側変換器及び受信側変換器の正電
極、負電極及び浮き電極の各電極指の弾性表面波の伝播
方向の幅ｄを、λ／１２となるように設定したことを特
徴とする。SUMMARY OF THE INVENTION A surface acoustic wave filter device according to the present invention comprises N (N is an integer of 2 or more) transversal type having a transmitting converter and a receiving converter formed on a quartz substrate. In the surface acoustic wave filter device in which these surface acoustic wave filters are cascade-connected, the transmission-side converter and the reception-side converter of each surface acoustic wave filter have a positive electrode, a negative electrode, and a short-circuit type. In the case where each has only a floating electrode and the wavelength of the basic surface acoustic wave is λ, the transmitting-side converter is a positive electrode in which each electrode finger is periodically formed with a center-to-center distance of λ. A negative electrode in which each electrode finger is periodically disposed at an intermediate position between the electrode fingers of the adjacent positive electrodes; and an electrode finger of the positive electrode and the negative electrode which are adjacent to each other. Only λ / 12 from the intermediate position between A floating electrode periodically arranged at a pitch of λ at a position deviated to the upstream side in the propagation direction of the surface acoustic wave, wherein the receiving-side converter is configured such that each electrode finger has a center-to-center distance of λ. Thus, the positive electrode periodically formed, the negative electrode in which each electrode finger is disposed at an intermediate position between the electrode fingers of the adjacent positive electrodes, and the positive electrode in which each electrode finger is adjacent to each other A floating electrode periodically arranged at a pitch of λ at a position deviated by λ / 12 to the downstream side in the propagation direction of the surface acoustic wave from an intermediate position between the electrode finger of the negative electrode and the electrode finger of the negative electrode. Wherein the width d in the propagation direction of the surface acoustic wave of each electrode finger of the positive electrode, the negative electrode, and the floating electrode of the transmission-side converter and the reception-side converter is set to be λ / 12. And
【００１０】[0010]
【作用】本発明では、送信側及び受信側変換器として一
方向性トランスジューサを用いる。そして、Ｎ個の送信
側変換器と受信側変換を用いてＮ個のフィルタ段を構成
し、これらフィルタ段を並列に配置すると共に互いに直
列に接続して１個の弾性表面波フィルタ装置を構成す
る。このように構成することにより、同一の通過帯域幅
のフィルタ装置を構成する場合、電極対数を減すことが
でき、縦長の形態とならないため、回路基板上に装着し
たときの実質的な占有面積を小さくすることができる。According to the present invention, a unidirectional transducer is used as a transmitter and a receiver converter. Then, N filter stages are configured using the N transmission-side converters and the reception-side conversions, and these filter stages are arranged in parallel and connected in series with each other to form one surface acoustic wave filter device. I do. By configuring in this way, when configuring a filter device having the same pass bandwidth, the number of electrode pairs can be reduced, and since the filter device does not have a vertically long shape, a substantial occupied area when mounted on a circuit board is achieved. Can be reduced.
【００１１】さらに、複数のフィルタ段を直列に接続し
て１個のフィルタ装置を構成していので、挿入損失は若
干増大するが、帯域外減衰量を大幅に改善することがで
きる。尚、一方向性トランスジューサは挿入損失を比較
的小さくすることができるようになったため、直列接続
することにより損失が若干増大してもユーザ仕様基準を
十分に満足することができる。Furthermore, since one filter device is formed by connecting a plurality of filter stages in series, the insertion loss slightly increases, but the amount of out-of-band attenuation can be greatly improved. Since the insertion loss of the one-way transducer can be made relatively small, even if the loss is slightly increased by connecting in series, the user specification standard can be sufficiently satisfied.
【００１２】さらに、基板材料としての水晶は温度変化
に対する通過帯域幅の変化（ＴＣＦ）が極めて小さいた
め、水晶基板上に一方向性トランスジューサを形成した
フィルタ装置の場合、温度変化に対する通過帯域幅の変
化が極めて小さいフィルタ装置を実現することができ
る。しかしながら、水晶はLiNbO3に比べて電気機械結合
係数が小さいため、上述した既知の一方向性トランスジ
ューサをそのまま適用したのでは挿入損失の面より実用
化することができない。しかも、電気機械結合係数の小
さい水晶基板の場合変換効率をアップさせるため電極の
対数を一層多くしなければならず、一層一方向に大型化
した構造になってしまう。このため、本発明では、各電
極指の電極幅をλ／12（λは基本弾性表面波の波長）に
設定し、浮き電極における非対称構造性を一層強く利用
して挿入損失を低減すると共に、複数のフィルタ段を並
列に配設して小型化を図る。このように構成することに
より、温度変化に対して極めて安定で、しかも小型化さ
れ且つ帯域外減衰量が一層改善された弾性表面波フィル
タ装置を実現することができる。Further, since the change of the pass band width (TCF) with respect to the temperature change is extremely small, the filter device having the unidirectional transducer formed on the quartz substrate has a small pass band width with respect to the temperature change. A filter device with a very small change can be realized. However, quartz has a smaller electromechanical coupling coefficient than LiNbO 3, and therefore cannot be put to practical use from the aspect of insertion loss if the above-mentioned known unidirectional transducer is applied as it is. In addition, in the case of a quartz substrate having a small electromechanical coupling coefficient, the number of pairs of electrodes must be increased in order to increase the conversion efficiency, resulting in a structure which is further enlarged in one direction. For this reason, in the present invention, the electrode width of each electrode finger is set to λ / 12 (λ is the wavelength of the basic surface acoustic wave), and the asymmetric structure of the floating electrode is more strongly used to reduce the insertion loss. A plurality of filter stages are arranged in parallel to reduce the size. With such a configuration, it is possible to realize a surface acoustic wave filter device that is extremely stable with respect to temperature changes, that is miniaturized, and that further improves the out-of-band attenuation.
【００１３】[0013]
【実施例】図１は、本発明による弾性表面波フィルタ装
置の一例の構成を示す線図的平面図である。本発明にお
いては、圧電性基板として水晶基板１を用いる。ＳＴカ
ットした水晶は−20℃〜80℃の温度範囲における周波数
に対する温度係数（ＴＣＦ）が1.6ppm／℃と極めて微小
である。ちなみに、128 °回転Ｙカット×方向伝播LiNb
O3のＴＣＦは−74ppm ／℃であるから、水晶基板は極め
て良好な温度特性を有し、温度変化による通過周波数帯
域の変動を極めて微小範囲内に維持することができる。
水晶基板１上に第１の送信側変換器２、第１の受信側変
換器３、第２の送信側変換器４及び第２の受信側変換器
５をそれぞれ形成する。第１の送信側変換器２と第１の
受信側変換３とで第１のフィルタ段を構成し、第２の送
信側変換器４と第２の受信側変換器５とにより第２のフ
ィルタ段を構成する。尚、これら変換器２〜５は、形成
されるフィルタ段が弾性波の伝播波方向に沿って互いに
平行になるように配置する。FIG. 1 is a diagrammatic plan view showing the structure of an example of a surface acoustic wave filter device according to the present invention. In the present invention, a quartz substrate 1 is used as a piezoelectric substrate. The ST-cut quartz has a very small temperature coefficient (TCF) of 1.6 ppm / ° C. with respect to frequency in a temperature range of −20 ° C. to 80 ° C. By the way, 128 ° rotation Y cut x direction propagation LiNb
Since the TCF of O 3 is −74 ppm / ° C., the quartz substrate has extremely good temperature characteristics, and the variation of the pass frequency band due to the temperature change can be maintained within a very small range.
On a crystal substrate 1, a first transmitting-side converter 2, a first receiving-side converter 3, a second transmitting-side converter 4, and a second receiving-side converter 5 are formed, respectively. The first transmitter-side converter 2 and the first receiver-side converter 3 constitute a first filter stage, and the second transmitter-side converter 4 and the second receiver-side converter 5 form a second filter stage. Make up the steps. The converters 2 to 5 are arranged so that the formed filter stages are parallel to each other along the propagation direction of the elastic wave.
【００１４】４個の変換器の構造は、一方向性トランス
ジューサとして同一の構造をなすため、第１の送信側変
換器の構造について詳細に説明する。第１の送信側変換
器２はインタディジタル型の正電極10及び負電極11と、
これら正電極と負電極との間に配置した短絡型浮き電極
12とを具える。本例では、これらの電極の電極指の幅は
λ／12に設定する。これらの電極は、水晶基板１上にア
ルミニウム層を蒸着又はスパッタリングし、フォトリソ
グラフィ法により形成することができる。尚、図面を明
瞭にするため、図面上各電極の対数は４対で表示した
が、通過帯域幅に応じて種々の対数に設定することがで
き、例えばディジタル通信用の狭帯域フィルタの場合例
えば 200〜400 対に設定することができる。正電極10の
電極指間のピッチ及び負電極11の電極指間のピッチは共
に基本弾性表面波の波長λに等しくなるように設定す
る。基本弾性表面波の波長λは、ｖを水晶基板における
弾性波の伝播速度とし、ｆ0 を中心周波数とした場合、
λ＝ｖ／ｆ0 となるように設定する。また、正電極10の
電極指と負電極１１の電極指との間の中心間距離はλ／
２に設定する。浮き電極12は、それぞれ対をなす電極指
を有し、これら電極指間のピッチはそれぞれλ／２に設
定する。浮き電極の各電極指は、これら電極指と隣接す
る正電極の電極指と負電極の電極指との間の中間点より
弾性波の伝播方向に見てλ／12の距離だけ手前側に偏位
させる。このように構成することにより、非対象構造に
基く浮き電極による機械的反射特性を一層有効に利用す
ることができ、励振された弾性表面波の大部分を図１の
右側すなわち受信側変換器３に向けて伝播させることが
できる。この結果、トランスジューサの一方向性が一層
増強され挿入損失を低減することができる。Since the structure of the four converters is the same as that of a one-way transducer, the structure of the first transmitting converter will be described in detail. The first transmitter 2 includes an interdigital positive electrode 10 and a negative electrode 11,
A short-circuit type floating electrode placed between these positive and negative electrodes
12 and so on. In this example, the width of the electrode fingers of these electrodes is set to λ / 12. These electrodes can be formed by depositing or sputtering an aluminum layer on the quartz substrate 1 and using a photolithography method. For clarity of the drawing, the logarithm of each electrode is shown as four pairs in the drawing, but can be set to various logarithms according to the pass band width. For example, in the case of a narrow band filter for digital communication, for example, 200 to 400 pairs can be set. The pitch between the electrode fingers of the positive electrode 10 and the pitch between the electrode fingers of the negative electrode 11 are both set to be equal to the wavelength λ of the basic surface acoustic wave. The wavelength λ of the basic surface acoustic wave is expressed as follows, where v is the propagation speed of the elastic wave on the quartz substrate and f 0 is the center frequency.
It is set so that λ = v / f 0 . The center-to-center distance between the electrode finger of the positive electrode 10 and the electrode finger of the negative electrode 11 is λ /
Set to 2. Each of the floating electrodes 12 has a pair of electrode fingers, and the pitch between these electrode fingers is set to λ / 2. Each electrode finger of the floating electrode is biased forward by a distance of λ / 12 when viewed in the direction of elastic wave propagation from an intermediate point between the electrode finger of the adjacent positive electrode and the electrode finger of the negative electrode. Position. With this configuration, the mechanical reflection characteristics of the floating electrode based on the asymmetric structure can be more effectively utilized, and most of the excited surface acoustic waves can be used on the right side of FIG. Can be propagated to As a result, the unidirectionality of the transducer is further enhanced, and the insertion loss can be reduced.
【００１５】水晶基板においては、この浮き電極の正電
極の電極指と負電極の電極指の中間点からの偏位量は一
方向性を高める上で極めて重要であり、その偏位量が小
さ過ぎると挿入損失が大きすぎてしまう、この偏位量に
ついて本発明者が種々の検討をした結果、浮き電極の電
極指の一部が正電極と負電極との間の中間点上に位置す
るのでは偏位量が少な過ぎ良好な損失特性が得られない
ことが判明した。従って、この浮き電極の偏位量は、浮
き電極の弾性波の伝播方向側の端縁が中間位置よりも弾
性表面波の伝播方向に見て手前側に位置するように設定
しなければならない。さらに、様々の検討結果より、浮
き電極の電極指の弾性表面波の伝播方向の中心位置が、
正電極と負電極との間の中間位置からほぼ電極指の幅だ
け離間する場合、浮き電極による反射波と正電極及び負
電極によって励振された弾性波との間の位相が互いに適
合し、最適な損失特性及び波形特性が得られる。In a quartz substrate, the amount of deviation of the floating electrode from the intermediate point between the electrode finger of the positive electrode and the electrode finger of the negative electrode is extremely important in improving the unidirectionality, and the amount of deviation is small. The present inventor has made various studies on the amount of deviation, which results in too much insertion loss if it is too long. As a result, a part of the electrode finger of the floating electrode is located on an intermediate point between the positive electrode and the negative electrode. It was found that the deviation was too small to obtain good loss characteristics. Therefore, the amount of deflection of the floating electrode must be set so that the edge of the floating electrode on the side in which the acoustic wave propagates is located closer to the near side than the intermediate position in the direction in which the surface acoustic wave propagates. Furthermore, from various examination results, the center position of the electrode finger of the floating electrode in the propagation direction of the surface acoustic wave is
When the electrode is separated from the intermediate position between the positive electrode and the negative electrode by almost the width of the electrode finger, the phases between the reflected wave from the floating electrode and the elastic wave excited by the positive and negative electrodes match each other, and are optimal. Loss characteristics and waveform characteristics can be obtained.
【００１６】これに対して、前述した特公平３−20929
号公報に記載の一方向性トランスジューサでは、正電極
及び負電極の電極幅をλ／８に設定し、浮き電極の電極
幅ｄを、λ／８＜ｄ＜λ／４に設定されている。しかし
ながら、正電極及び負電極の電極幅をλ／８に設定する
と、正電極と負電極との間の中心間距離がλ／２である
から、浮き電極を形成できる範囲は３λ／８となってし
まう。この場合、浮き電極と正電極及び負電極との間の
スペースを考慮すると、浮き電極の正電極と負電極との
間の中心位置から偏位させることができる許容範囲が小
さすぎ、従って十分な非対称構造とすることができな
い。すなわち、正電極と負電極との間の中間位置から浮
き電極を偏位させることができるスペースが小さすぎ、
非対称構造による効果を有効に利用することができず、
従ってそのまま水晶基板に適用したのでは、ユーザ仕様
基準を満たす損失特性を達成することができない。On the other hand, the aforementioned Japanese Patent Publication No. 3-20929
In the one-way transducer described in the publication, the electrode width of the positive electrode and the negative electrode is set to λ / 8, and the electrode width d of the floating electrode is set to λ / 8 <d <λ / 4. However, if the electrode width of the positive electrode and the negative electrode is set to λ / 8, the center electrode distance between the positive electrode and the negative electrode is λ / 2, so that the range in which the floating electrode can be formed is 3λ / 8. Would. In this case, considering the space between the floating electrode, the positive electrode, and the negative electrode, the allowable range in which the floating electrode can be deviated from the center position between the positive electrode and the negative electrode is too small, and therefore is not sufficient. It cannot be an asymmetric structure. That is, the space where the floating electrode can be deviated from the intermediate position between the positive electrode and the negative electrode is too small,
The effect of the asymmetric structure cannot be used effectively,
Therefore, if it is applied to a quartz substrate as it is, it is not possible to achieve a loss characteristic satisfying a user specification standard.
【００１７】第１の受信側変換器３は正電極13及び負電
極14とこれらの電極間に配置した短絡型浮き電極15とを
有する。また、第２の送信側変換器４も正電極16及び負
電極17とこれら電極間に配置した短絡型浮き電極18とを
有する。第１の受信側変換器３の正電極13と第２の送信
側変換器４の正電極16とを基板上に形成した導体パター
ン19を介して電気的に接続する。さらに、第２の受信側
変換器５も同様に正電極20及び負電極21とこれら電極間
に配置した短絡型浮き電極22とを有する。第１の送信側
変換器２の正電極10を信号入力端子23に接続し、第２の
受信側変換器５の正電極20は信号出力端子24に接続す
る。尚、導体パターン19に所定のインピダンスを結合し
てインピダンス整合させることが好ましい。The first receiving-side converter 3 has a positive electrode 13 and a negative electrode 14, and a short-circuit type floating electrode 15 disposed between these electrodes. Further, the second transmitter-side converter 4 also has a positive electrode 16 and a negative electrode 17, and a short-circuit type floating electrode 18 disposed between these electrodes. The positive electrode 13 of the first receiving converter 3 and the positive electrode 16 of the second transmitting converter 4 are electrically connected via a conductor pattern 19 formed on a substrate. Further, the second receiving-side converter 5 similarly has a positive electrode 20 and a negative electrode 21, and a short-circuit type floating electrode 22 disposed between these electrodes. The positive electrode 10 of the first transmitter 2 is connected to a signal input terminal 23 and the positive electrode 20 of the second receiver 5 is connected to a signal output terminal 24. It is preferable that a predetermined impedance is coupled to the conductor pattern 19 so that the impedance is matched.
【００１８】濾波されるべき電気信号は入力端子23及び
アース端子を経て第１の送信側変換器に供給する。第１
の送信側変換器２によって励振された弾性波は矢印ａ方
向に伝播し、第１の受信側変換器３でピックアップされ
て電気信号に変換される。この電気信号５は第２の送信
側変換器４に供給され、この第２の送信側変換器４によ
り励振された弾性波は矢印ｂ方向に伝播し、第２の受信
側変換器５によりピックアップされて電気信号変換さ
れ、信号出力端子24から取り出される。従って、濾波さ
れべき信号は、２個の直列接続したフィルタ段によって
２回濾波されることになる。The electrical signal to be filtered is supplied to a first transmitting converter via an input terminal 23 and a ground terminal. First
The elastic wave excited by the transmitting-side transducer 2 propagates in the direction of arrow a, is picked up by the first receiving-side transducer 3, and is converted into an electric signal. The electric signal 5 is supplied to the second transmitter 4, and the elastic wave excited by the second transmitter 4 propagates in the direction of the arrow b and is picked up by the second receiver 5. Then, the signal is converted into an electric signal, and is extracted from the signal output terminal 24. Thus, the signal to be filtered will be filtered twice by the two series connected filter stages.
【００１９】図２は本発明による弾性表面波フィルタ装
置の変形例を示す線図的平面図である。尚、図１で用い
た部材と同一の部材には同一の符号を付して説明する。
本例では、第１及び第２の送信側変換器２及び４を弾性
表面波の伝播方向と直交する方向に延在する軸線上に沿
って配置すると共に第１及び第２の受信側変換器３及び
５も同様に弾性表面波の伝播方向と直交する方向に延在
する軸線に沿って配置し、第１の受信側変換器の正電極
13と第２の送信側変換器４の正電極16とを基板上に形成
した導体パターン19によって接続する。このように各変
換器を配置することにより、濾波すべき信号が入力する
第１の送信側変換器２と出力信号が発生する第２の受信
側変換器５とを遠ざけることができ、第１の送信側変換
器２で励振された弾性表面波が第２の受信側変換器５と
電磁的に結合する不都合を回避することができる。FIG. 2 is a schematic plan view showing a modification of the surface acoustic wave filter device according to the present invention. The same members as those used in FIG. 1 will be described with the same reference numerals.
In this example, the first and second transmitting converters 2 and 4 are arranged along an axis extending in a direction orthogonal to the propagation direction of the surface acoustic wave, and the first and second receiving converters are arranged. Similarly, 3 and 5 are arranged along an axis extending in a direction orthogonal to the propagation direction of the surface acoustic wave, and the positive electrode of the first receiving-side transducer is arranged.
13 and the positive electrode 16 of the second transmitter 4 are connected by a conductor pattern 19 formed on the substrate. By arranging the respective converters in this manner, the first transmitting converter 2 to which the signal to be filtered is input and the second receiving converter 5 from which the output signal is generated can be kept away from the first converter. The disadvantage that the surface acoustic wave excited by the transmitting-side converter 2 of the above-mentioned configuration is electromagnetically coupled to the second receiving-side converter 5 can be avoided.
【００２０】図３は本発明になる弾性表面波フィルタ装
置の別の変形例を示す。本例では、図２に示すフィルタ
装置にガード電極30及び31を形成し、これらガード電極
により各変換器で励振され又は入力した弾性表面波が他
の変換器に入射しないようにする。特に、第１の受信側
変換器３と第２の送信側変換器４とを接続する導体パタ
ーン19には不所望な信号が入力し易いため、ガード電極
30及び31を導体パターン19の少なくともその一部に沿っ
て形成することにより変換器間の電磁結合を防止すると
共にノイズの発生を一層低減することができる。FIG. 3 shows another modification of the surface acoustic wave filter device according to the present invention. In this example, guard electrodes 30 and 31 are formed in the filter device shown in FIG. 2 so that the surface of the surface acoustic wave excited or input by each converter is prevented from entering other converters by the guard electrodes. In particular, since an undesired signal is easily input to the conductor pattern 19 connecting the first receiving-side converter 3 and the second transmitting-side converter 4, the guard electrode
By forming the conductors 30 and 31 along at least a part of the conductor pattern 19, it is possible to prevent electromagnetic coupling between the converters and to further reduce the generation of noise.
【００２１】図４は本発明による弾性表面波フィルタ装
置の別の変形例を示す線図的平面図である。本例では送
信側変換器の対数と受信側変換器の対数を相異させる。
このように送信側の対数と受信側の対数を相異させるこ
とにより、トランスバーサル型のフィルタ装置に比べて
全体としての対数を1/2 に減少させても同一の通過帯域
幅のフィルタ装置を実現することができる。さらに、本
例では、１個のガード電極32を用いて第１のフィルタ段
と第２のフィルタ段との間並びに送信側変換器と受信側
変換器との間で不所望なノイズの侵入を防止する。尚、
本例では、第１の受信側変換器と第２の送信側変換器と
は、ボンデングワイヤ又は基板を収納するパッケージに
形成した導体パターンを介して相互接続することができ
る。FIG. 4 is a schematic plan view showing another modification of the surface acoustic wave filter device according to the present invention. In this example, the logarithm of the transmitting converter is different from the logarithm of the receiving converter.
By making the logarithm of the transmitting side and the logarithm of the receiving side different in this way, even if the overall logarithm is reduced by half compared to the transversal type filter device, a filter device having the same pass bandwidth can be obtained. Can be realized. Furthermore, in the present example, one guard electrode 32 is used to prevent unwanted noise from entering between the first filter stage and the second filter stage and between the transmitting converter and the receiving converter. To prevent. still,
In this example, the first receiving-side converter and the second transmitting-side converter can be interconnected via a bonding wire or a conductor pattern formed on a package containing the substrate.
【００２２】次に、実験結果について説明する。１個の
フィルタ段から成る通常のトランスバーサル型の一方向
性弾性表面フィルタ装置と、図１に示す２個のフィルタ
段から成る弾性表面波フィルタ装置を試作して特性評価
を行なった。電極の対数は共に同一に設定し、中心周波
数は240MHzに設定した。図５に特性評価の結果を示す。
実線は本発明による弾性表面波フィルタ装置の特性を示
し、破線は従来の一方向性弾性表面波フィルタ装置の結
果を示す。図５から明らかなように、２個のフィルタ装
置を直列接続することにより、挿入損失は3.5dB から７
dBと若干増大するが、帯域外減衰量は大幅に改善され
た。Next, the experimental results will be described. An ordinary transversal type unidirectional surface acoustic wave filter device having one filter stage and a surface acoustic wave filter device having two filter stages shown in FIG. 1 were prototyped and their characteristics were evaluated. The number of electrodes was set to be the same, and the center frequency was set to 240 MHz. FIG. 5 shows the results of the characteristic evaluation.
The solid line shows the characteristics of the surface acoustic wave filter device according to the present invention, and the broken line shows the results of the conventional unidirectional surface acoustic wave filter device. As is apparent from FIG. 5, the insertion loss is reduced from 3.5 dB to 7 by connecting two filter devices in series.
Although increased slightly to dB, the out-of-band attenuation was greatly improved.
【００２３】本発明は上述した実施例だけに限定されず
種々の変更や変形が可能である。例えば、上述した実施
例では４個の変換器を用いて２個のフィルタ段を形成し
たが、６個或いは８個の変換器を用いて３個又は４個の
フィルタ段を構成することも可能である。The present invention is not limited to the above-described embodiment, and various changes and modifications are possible. For example, in the above-described embodiment, two filter stages are formed using four converters. However, three or four filter stages can be formed using six or eight converters. It is.
【００２４】[0024]
【発明の効果】以上説明したように本発明によれば、複
数個の送信側変換器及び受信側変換器を用い、複数個の
フィルタ段を構成し、これらフィルタ段を直列接続して
いるから、回路基板に装着した場合の実質的な占有面積
を小さくすることができると共に帯域外の減衰量を一層
大幅に改善することができる。また、基板材料としてＴ
ＣＦの小さい水晶を用い、変換器として正電極及び負電
極とこれら電極間に配置した幅λ／12の短絡型浮き電極
とを具え、浮き電極を正電極と負電極の中間装置よりλ
／12の距離だけ偏位させた構造の変換器を用いたことに
より、挿入損失が小さくしかも温度変化に対して極めて
安定なフィルタ装置を構成できるので、このような変換
器を有するフィルタ段を直列接続することにより、温度
変化に対して極めて安定で、小型且つ帯域外減衰量が改
善された弾性表面波フィルタ装置を実現することができ
る。As described above, according to the present invention, a plurality of filter stages are formed using a plurality of transmitter converters and receiver converters, and these filter stages are connected in series. In addition, it is possible to reduce the substantial occupied area when mounted on the circuit board and to further greatly improve the attenuation outside the band. In addition, T
A quartz crystal with a small CF is used, and a positive electrode and a negative electrode are provided as a converter, and a short-circuit type floating electrode having a width of λ / 12 is disposed between these electrodes.
Since a converter having a structure deviated by a distance of / 12 is used, a filter device having a small insertion loss and extremely stable against a temperature change can be formed. The connection makes it possible to realize a surface acoustic wave filter device that is extremely stable against temperature changes, is small, and has improved out-of-band attenuation.
【図１】図１は本発明による弾性表面波フィルタ装置の
一例を示す線図的平面図である。FIG. 1 is a schematic plan view showing an example of a surface acoustic wave filter device according to the present invention.
【図２】図２は本発明による弾性表面波フィルタ装置の
変形例を示す線図的平面図である。FIG. 2 is a schematic plan view showing a modified example of the surface acoustic wave filter device according to the present invention.
【図３】図３は本発明による弾性表面波フィルタ装置の
変形例を示す線図的平面図である。FIG. 3 is a schematic plan view showing a modified example of the surface acoustic wave filter device according to the present invention.
【図４】図４は本発明による弾性表面波フィルタ装置の
変形例を示す線図的平面図である。FIG. 4 is a schematic plan view showing a modified example of the surface acoustic wave filter device according to the present invention.
【図５】図５はトランスバーサル型の素子と本発明によ
る素子との比較実験結果を示すグラフである。FIG. 5 is a graph showing the results of a comparative experiment between a transversal device and a device according to the present invention.
１ 圧電性基板 ２ 第１の送信側変換器 ３ 第１の受信側変換器 ４ 第２の送信側変換器 ５ 第２の受信側変換器 10, 13, 16, 20 正電極（負電極） 11, 14, 17, 21 負電極（正電極） 15 浮き電極 19 導体パターン 23 信号入力端子 24 信号出力端子 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 1st transmitting side converter 3 1st receiving side converter 4 2nd transmitting side converter 5 2nd receiving side converter 10, 13, 16, 20 Positive electrode (negative electrode) 11 , 14, 17, 21 Negative electrode (positive electrode) 15 Floating electrode 19 Conductor pattern 23 Signal input terminal 24 Signal output terminal
───────────────────────────────────────────────────── フロントページの続き (72)発明者 堀尾 保文 愛知県名古屋市瑞穂区白砂町２丁目74番 地 ナビシティ白砂202 (72)発明者 鈴木 健司 愛知県名古屋市瑞穂区師長町43−１ 師 長社宅104 (56)参考文献 特開 昭61−6916（ＪＰ，Ａ) 特開 昭62−61413（ＪＰ，Ａ) 特開 昭49−66051（ＪＰ，Ａ) 特開 平３−133209（ＪＰ，Ａ) 特公 昭62−17406（ＪＰ，Ｂ２) 電子通信学会技術研究報告 ＵＳ85− 11 電子通信学会技術研究報告 ＵＳ84− 18 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasufumi Horio 2-74 Shirasuna-cho, Mizuho-ku, Nagoya-shi, Aichi Prefecture Navicity Shirasuna 202 (72) Inventor Kenji Suzuki 43-1 Shimagamachi, Mizuho-ku, Nagoya-shi, Aichi JP-A-61-6916 (JP, A) JP-A-62-6413 (JP, A) JP-A-49-66051 (JP, A) JP-A-3-133209 (JP) , A) Tokiko 62-17406 (JP, B2) Technical report of IEICE Technical Report US85-11 Technical report of IEICE Technical Report US84-18
Claims (6)
信側変換器を有するＮ個（Ｎは２以上の整数）のトラン
スバーサル型の弾性表面波フィルタを具え、これら弾性
表面波フィルタを縦続接続した弾性表面波フィルタ装置
において、 各弾性表面波フィルタの送信側変換器及び受信側変換器
が、正電極、負電極及び短絡型の浮き電極のみをそれぞ
れ有し、 基本弾性表面波の波長をλとした場合に、前記送信側変
換器が、各電極指がλの中心間距離を以って周期的に形
成されている正電極と、各電極指が、互いに隣接する正
電極の電極指間の中間位置に周期的に配置されている負
電極と、各電極指が、互いに隣接する正電極の電極指と
負電極の電極指との間の中間位置からλ／１２だけ弾性
表面波の伝播方向の上流側に偏位した位置にλのピッチ
で周期的に配置されている浮き電極とを有し、 前記受信側変換器が、各電極指がλの中心間距離を以っ
て周期的に形成されている正電極と、各電極指が、互い
に隣接する正電極の電極指間の中間位置に配置されてい
る負電極と、各電極指が、互いに隣接する正電極の電極
指と負電極の電極指との間の中間位置からλ／１２だけ
弾性表面波の伝播方向の下流側に偏位した位置にλのピ
ッチで周期的に配置されている浮き電極とを有し、 前記送信側変換器及び受信側変換器の正電極、負電極及
び浮き電極の各電極指の弾性表面波の伝播方向の幅ｄ
を、λ／１２となるように設定したことを特徴とする弾
性表面波フィルタ装置。1. A transversal type surface acoustic wave filter having a transmitting converter and a receiving converter formed on a quartz substrate, wherein N is an integer of 2 or more. In the cascade-connected surface acoustic wave filter device, the transmitting converter and the receiving converter of each surface acoustic wave filter each have only a positive electrode, a negative electrode, and a short-circuit type floating electrode, and the wavelength of the basic surface acoustic wave. When λ is λ, the transmitting-side converter is a positive electrode in which each electrode finger is periodically formed with a center distance of λ, and each electrode finger is an electrode of a positive electrode adjacent to each other. A negative electrode periodically arranged at an intermediate position between the fingers, and each electrode finger is a surface acoustic wave by λ / 12 from an intermediate position between an adjacent positive electrode electrode and a negative electrode electrode finger. Λ pitch at a position deviated upstream in the propagation direction of The receiving-side converter has a positive electrode in which each electrode finger is periodically formed with a center-to-center distance of λ, and each of the electrode fingers has a floating electrode. A negative electrode disposed at an intermediate position between the electrode fingers of the adjacent positive electrodes, and each of the electrode fingers is separated by λ / λ from an intermediate position between the electrode fingers of the adjacent positive and negative electrodes. A floating electrode periodically arranged at a pitch of λ at a position deviated to the downstream side in the propagation direction of the surface acoustic wave by 12; a positive electrode of the transmitting converter and a positive electrode of the receiving converter; The width d of each electrode finger of the electrode and the floating electrode in the propagation direction of the surface acoustic wave
Is set to be λ / 12.
の正電極と後段の弾性表面波フィルタの送信側変換器の
正電極とを前記水晶基板に形成した導体パターン、ボン
デングワイヤ、金リボン又は前記水晶基板を収納するパ
ッケージに形成した導体パターンにより相互接続したこ
とを特徴とする請求項１に記載の弾性表面波フィルタ装
置。2. A conductor pattern, a bonding wire, and a metal having a positive electrode of a receiving converter of a front surface acoustic wave filter and a positive electrode of a transmitting converter of a subsequent surface acoustic wave filter formed on the quartz substrate. 2. The surface acoustic wave filter device according to claim 1, wherein the surface acoustic wave filter devices are connected to each other by a conductor pattern formed on a ribbon or a package containing the quartz substrate .
ード電極を配置し、隣接する変換器が電磁結合しないよ
うに構成したことを特徴とする請求項１又は２に記載の
弾性表面波フィルタ装置。3. The surface acoustic wave filter device according to claim 1, wherein a guard electrode is arranged between adjacent surface acoustic wave filters so that adjacent converters are not electromagnetically coupled. .
に各弾性表面波フィルタの送信側変換器と受信側変換器
との間にガード電極を配置したことを特徴とする請求項
１又は２に記載の弾性表面波フィルタ装置。4. A guard electrode according to claim 1, wherein guard electrodes are arranged between adjacent surface acoustic wave filters and between a transmitter converter and a receiver converter of each surface acoustic wave filter. Surface acoustic wave filter device.
において、前段の弾性表面波フィルタの受信側変換器の
正電極と後段の弾性表面波フィルタの送信側変換器の正
電極とを圧電性基板上に形成した導体パターンにより電
気的に接続し、この導体パターンの少なくとも一部に沿
ってガード電極を形成したことを特徴とする弾性表面波
フィルタ装置。5. The surface acoustic wave filter device according to claim 2, wherein the positive electrode of the receiving-side converter of the preceding surface acoustic wave filter and the positive electrode of the transmitting-side converter of the subsequent surface acoustic wave filter are piezoelectrically connected. A surface acoustic wave filter device comprising: an electrically connected conductive pattern formed on a conductive substrate; and a guard electrode formed along at least a part of the conductive pattern.
信側変換器の電極対数と受信側変換器の電極対数とを互
いに相異させたことを特徴とする請求項１から５までの
いずれか１項に記載の弾性表面波フィルタ装置。6. The apparatus according to claim 1, wherein the number of electrode pairs of the transmitting converter and the number of electrode pairs of the receiving converter of at least one surface acoustic wave filter are different from each other. 2. The surface acoustic wave filter device according to claim 1.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5041220A JP2915735B2 (en) | 1993-03-02 | 1993-03-02 | Surface acoustic wave filter device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5041220A JP2915735B2 (en) | 1993-03-02 | 1993-03-02 | Surface acoustic wave filter device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH06260875A JPH06260875A (en) | 1994-09-16 |
| JP2915735B2 true JP2915735B2 (en) | 1999-07-05 |
Family
ID=12602317
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP5041220A Expired - Fee Related JP2915735B2 (en) | 1993-03-02 | 1993-03-02 | Surface acoustic wave filter device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2915735B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112653413A (en) * | 2020-12-16 | 2021-04-13 | 武汉大学 | System and method for adjusting effective electromechanical coupling coefficient of ultrahigh frequency bulk acoustic wave resonator |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5434505B2 (en) * | 1972-10-30 | 1979-10-27 | ||
| JPS616916A (en) * | 1984-06-20 | 1986-01-13 | Kazuhiko Yamanouchi | Internal reflection type unidirectional surface acoustic wave converter having floating electrode |
| JPS6217406A (en) * | 1985-07-16 | 1987-01-26 | Sakagami Seisakusho:Kk | Cushion seal |
| JPS6261413A (en) * | 1985-09-11 | 1987-03-18 | Toyo Commun Equip Co Ltd | Shield pattern for multi-stage connection saw multiplex mode filter |
| JP3175830B2 (en) * | 1989-10-19 | 2001-06-11 | 東洋通信機株式会社 | One-way SAW filter |
-
1993
- 1993-03-02 JP JP5041220A patent/JP2915735B2/en not_active Expired - Fee Related
Non-Patent Citations (2)
| Title |
|---|
| 電子通信学会技術研究報告 ＵＳ８４−１８ |
| 電子通信学会技術研究報告 ＵＳ８５−１１ |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH06260875A (en) | 1994-09-16 |
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