JPH10135780A - Structure of double mode saw filter - Google Patents
Structure of double mode saw filterInfo
- Publication number
- JPH10135780A JPH10135780A JP30593996A JP30593996A JPH10135780A JP H10135780 A JPH10135780 A JP H10135780A JP 30593996 A JP30593996 A JP 30593996A JP 30593996 A JP30593996 A JP 30593996A JP H10135780 A JPH10135780 A JP H10135780A
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- Prior art keywords
- electrode
- idt
- center
- spurious
- frequency
- Prior art date
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- Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は共振子型の弾性表面
波フィルタ（以下ＳＡＷフィルタと称す）に関し、特に
通過帯域の低周波側のスプリアスを低減した１−３次縦
結合二重モードＳＡＷフィルタに関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonator type surface acoustic wave filter (hereinafter referred to as "SAW filter"), and more particularly to a 1-3 order longitudinally coupled double mode SAW filter with reduced spurious on the low frequency side of a pass band. About.
【０００２】[0002]
【従来の技術】近年、ＳＡＷフィルタは小型化、高周波
化、量産性等に優れているため、携帯電話をはじめとす
る無線機に多く利用されている。特に最近のＰＨＳ、コ
ードレス電話等では第一ＩＦフィルタの高周波化と広帯
域化が要求され、この要件を満たし得るのはＳＡＷフィ
ルタのみである。共振子型ＳＡＷフィルタの広帯域化を
図る手段として１次と３次のモードを利用した１次−３
次縦結合二重モードＳＡＷフィルタが用いられている。
図５はその一例を示す模式的平面図で、矩形状の圧電性
基板１１の主面上に表面波の伝搬方向に沿って３個のイ
ンターディジタルトランスジューサ（以下ＩＤＴと称
す）１２、１３、１４を配置し、その両側にグレーティ
ング型の反射器１５、１６を配置する。ＩＤＴ１２〜１
４はそれぞれ互いに間挿し合う複数本の電極指を有する
一対のくし形電極により構成されている。ＩＤＴ１２〜
１４の一方のくし型電極はアース電位に接続され、他方
のくし形電極は入力または出力に電気的に接続されてい
る。2. Description of the Related Art In recent years, SAW filters have been widely used in wireless devices such as mobile phones, because of their excellent miniaturization, high frequency, mass productivity, and the like. Particularly in recent PHS, cordless telephones, etc., the first IF filter is required to have a higher frequency and a wider band, and only the SAW filter can satisfy this requirement. First-order-3 using first- and third-order modes as means for widening the band of a resonator-type SAW filter
A next-order longitudinally-coupled dual-mode SAW filter is used.
FIG. 5 is a schematic plan view showing an example of this, in which three interdigital transducers (hereinafter referred to as IDTs) 12, 13, and 14 are arranged on the main surface of a rectangular piezoelectric substrate 11 along the propagation direction of the surface wave. And grating type reflectors 15 and 16 are arranged on both sides thereof. IDT12-1
Reference numeral 4 denotes a pair of comb-shaped electrodes each having a plurality of electrode fingers interposed therebetween. IDT12 ~
One of the 14 comb electrodes is connected to the ground potential, and the other comb electrode is electrically connected to the input or output.
【０００３】図５に示す反射器１５、１６はＩＤＴ１
２、１４からの漏洩表面波を反射する機能を有し、ＩＤ
Ｔ１２〜１４で励起される弾性表面波のエネルギーを反
射器１５、１６間に閉じ込めることにより、１次モード
と３次モードのＱ値を高める作用をする。このとき、２
次モードも当然励起されるが、該モードの変位分布は表
面波の伝搬方向にＩＤＴ１３の中心に対し対称に分布す
るため、発生電荷も同様にＩＤＴ１３の中心に対し対称
となり入出力ＩＤＴ間で相殺されて実質上励起されない
のに等しく１次モードと３次モードのみを利用すること
が可能となる。また、通過域のカットオフ特性を改善
し、帯域外の減衰量を大きくする手段として図６に示す
ように１次−３次縦結合二重モードＳＡＷフィルタを二
段縦続接続構成とすることが一般的に行われている。図
７は図６の二段縦続接続した縦結合二重モードＳＡＷフ
ィルタの特性を示す図であり、圧電基板は３６°Ｙ−Ｘ
ＬｉＴａＯ３、中心周波数Ｆ０＝１１０ＭＨｚ、通過帯
域幅１．８ＭＨｚ、中央のＩＤＴ６の電極対数は６６．
５対、ＩＤＴ５、７の電極対数を３３．５対、反射器２
５本とした場合の濾波特性例である。同図から明らかな
ように通過帯域の低周波側の減衰量がスプリアスにより
劣化していることが分かる。The reflectors 15 and 16 shown in FIG.
It has the function of reflecting the leaky surface waves from 2, 14
By confining the energy of the surface acoustic wave excited at T12 to T14 between the reflectors 15 and 16, the Q value of the primary mode and the tertiary mode is increased. At this time, 2
The next mode is naturally excited, but the displacement distribution of the mode is distributed symmetrically with respect to the center of the IDT 13 in the propagation direction of the surface wave, so that the generated charges are similarly symmetric with respect to the center of the IDT 13 and cancel between the input and output IDTs. Thus, it is possible to use only the first-order mode and the third-order mode, which are substantially not excited. As a means for improving the cutoff characteristic of the pass band and increasing the amount of attenuation outside the band, a primary-tertiary longitudinally coupled dual-mode SAW filter having a two-stage cascade configuration as shown in FIG. Generally done. FIG. 7 is a diagram showing the characteristics of the vertically coupled dual mode SAW filter of FIG. 6 which is cascaded in two stages.
LiTaO3, center frequency F0 = 110 MHz, pass band width 1.8 MHz, number of electrode pairs of IDT 6 at the center is 66.
5 pairs, 33.5 electrode pairs for IDTs 5 and 7, reflector 2
It is an example of a filtering characteristic in the case of five lines. As can be seen from the figure, the attenuation on the low frequency side of the pass band is degraded due to spurious.
【０００４】一般的に低周波側の減衰特性を改善する手
段として、反射器の対数を少なくする、ＩＤＴに重み付
けをする、ＩＤＴの電極膜厚を厚くすると云った手法が
用いられてきた。また、特開平７−１３１２８１号に上
述の共振子型フィルタとは異なるトランスバーサル型フ
ィルタの一種である多電極型弾性表面波フィルタ（ Ｉ
ＩＤＴ型）におけるスプリアス除去手段が開示されてお
り、 ＩＤＴの電極指をまびき、そこにダミー電極を形
成してその過半数を基準電位であるアース電極に、他を
入出力側電極に接続することにより、直達波レベルを低
減し、スプリアスの低減ができることを示している。In general, as a means for improving the attenuation characteristic on the low frequency side, a method of reducing the logarithm of the reflector, weighting the IDT, and increasing the electrode thickness of the IDT has been used. Japanese Patent Application Laid-Open No. 7-131281 discloses a multi-electrode surface acoustic wave filter (I) which is a type of transversal filter different from the above-described resonator filter.
A spurious elimination means in an IDT type is disclosed. Sputtering an electrode finger of the IDT, forming a dummy electrode there, connecting the majority to a ground electrode which is a reference potential, and connecting the other to an input / output side electrode. This shows that the direct wave level can be reduced and spurious can be reduced.
【０００５】[0005]
【発明が解決しようとする課題】しかしながら、反射器
の本数を少なくすると励起される振動モードのＱ値が劣
化し、フィルタを構成する場合には挿入損失の増大を来
すという問題があるためむやみに本数を減らすことはで
きない。ＩＤＴに重み付けをするあるいはＩＤＴの電極
膜厚を厚くする方法は通過帯域幅を広げることになり、
所望値の帯域幅を実現するためには重み付けなしのＩＤ
Ｔあるいは電極膜厚の薄いＩＤＴに比べ、ＩＤＴ対数を
増加する必要があり、昨今の小型化への要求を満足でき
ないという問題がある。However, when the number of reflectors is reduced, the Q value of the vibration mode to be excited is deteriorated, and when a filter is formed, there is a problem that the insertion loss is increased. The number cannot be reduced. The method of weighting the IDT or increasing the electrode film thickness of the IDT increases the pass bandwidth,
Unweighted ID to achieve desired bandwidth
It is necessary to increase the IDT logarithm as compared with T or an IDT having a thin electrode film, and there is a problem that the recent demand for miniaturization cannot be satisfied.
【０００６】また、前記公開公報ではスプリアス低減方
法ではどの周波数でスプリアス低減効果が現れるのか全
く検討されておらず、実際にはＩＩＤＴ型ＳＡＷフィル
タにおいても特定の周波数に出現するスプリアスを除去
することは極めて困難であり、この方法では実現できな
いという問題があった。まして、ＩＩＤＴ型ＳＡＷフィ
ルタにおける上述のようなスプリアス低減手段を直ちに
共振子型１次−３次型縦結合二重モードＳＡＷフィルタ
に適用することはできなかった。本発明は上記問題を解
決するためになされたものであって、共振子型１次−３
次縦結合二重モードＳＡＷフィルタにおいて、通過域よ
り低周波側のスプリアスによる減衰量低減を任意の周波
数において改善する手段を提供することを目的とする。[0006] Further, the above publication does not consider at what frequency the spurious reduction effect appears in the spurious reduction method. In practice, it is impossible to remove spurious that appears at a specific frequency even in an IIDT type SAW filter. There is a problem that it is extremely difficult and cannot be realized by this method. Further, the above-mentioned spurious reduction means in the IIDT type SAW filter cannot be immediately applied to the resonator type primary-tertiary type longitudinally coupled double mode SAW filter. The present invention has been made to solve the above-mentioned problem, and has been made in consideration of the resonator type primary-3.
It is an object of the present invention to provide a means for improving the attenuation reduction due to spurious components on the lower frequency side than the pass band at an arbitrary frequency in a secondary longitudinally coupled dual mode SAW filter.
【０００７】[0007]
【課題を解決するための手段】上記目的を達成するため
に本発明に係る二重モードＳＡＷフィルタの請求項１記
載の発明は、圧電基板上に３個のＩＤＴとその両側に反
射器を表面波の伝搬方向に沿って配置した１次−３次縦
結合二重モードＳＡＷフィルタにおいて、中央に位置す
る中央ＩＤＴの中心軸を基準としてほぼ対称に位置する
接地側電極指の少なくとも１組を浮き電極指に置き換え
ることを特徴とする二重モードＳＡＷフィルタの構造で
ある。請求項２記載の発明は、中央ＩＤＴの接地側電極
指の本数をＮ’、浮き電極に置き換えた前記接地側電極
指の中央ＩＤＴ端部からのナンバリングをＮ、フィルタ
通過域の中心周波数をＦ０としたとき、 （Ｆ− Ｆ0）／ Ｆ0＝０．１３５Ｎ／（（Ｎ’＋１）／
２）−０．０６９ の式を満たす周波数Ｆ近傍において、スプリアスを抑圧
することを特徴とする請求項１記載の二重モードＳＡＷ
フィルタの構造である。According to a first aspect of the present invention, there is provided a dual mode SAW filter comprising three IDTs on a piezoelectric substrate and reflectors on both sides thereof. In a first-order / third-order longitudinally-coupled dual-mode SAW filter arranged along the propagation direction of a wave, at least one pair of ground-side electrode fingers located approximately symmetrically with respect to the central axis of a central IDT located at the center is lifted. This is a structure of a dual mode SAW filter characterized by being replaced with an electrode finger. The number of ground-side electrode fingers of the central IDT is N ', the number of the ground-side electrode fingers replaced with floating electrodes from the center IDT end is N, and the center frequency of the filter passband is F0. Then, (F−F0) /F0=0.135 N / ((N ′ + 1) /
2) The dual mode SAW according to claim 1, wherein spurious is suppressed in the vicinity of a frequency F which satisfies -0.069.
It is a structure of a filter.
【０００８】[0008]
【発明の実施の形態】以下本発明を図面に示した実施の
形態に基づいて詳細に説明する。図１は本発明に係る二
重モードＳＡＷフィルタの一実施例の電極構造を示す模
式的平面図であって、圧電基板上に３個のＩＤＴ５、
６、７を表面波の伝搬方向に沿って配置し、その両側に
前記ＩＤＴより漏洩した表面波を電極中央へ反射するグ
レイティング反射器等の反射器８、９を配設する。DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1 is a schematic plan view showing an electrode structure of an embodiment of a dual mode SAW filter according to the present invention, in which three IDTs 5 are provided on a piezoelectric substrate.
6 and 7 are arranged along the propagation direction of the surface wave, and reflectors 8 and 9 such as a grating reflector for reflecting the surface wave leaked from the IDT to the center of the electrode are arranged on both sides thereof.
【０００９】本発明に係るＩＤＴの特徴は中央のＩＤＴ
６にあり、更に詳しくはアース側くし形電極６ｂの電極
指を該ＩＤＴの中央より左右対称に配置し、図１に示す
ようにその両側から順に番号を付けたとき、左右の同番
号（この図においては３番目）の電極指を端子側にもア
ース側にも接続しない浮き電極指とするものである。図
１（ａ）に示したＩＤＴ６の電極構成の平面図の一部
（中心より左半分）を図１（ｂ）に拡大して示す。図１
（ｂ）はくし形電極６ｂの左から３番目の電極指を浮き
電極指に置き換えたものであり、同様にくし形電極６ｂ
の中心より右側においても右端から３番目の電極指を浮
き電極指で置換する。ここでくし形電極６ｂの電極指本
数をＮ’本としたとき、くし形電極６ｂの電極指が奇数
であれば、中央の電極指はＩＤＴ６の中心と一致し、左
あるいは右から数えても（Ｎ’＋１）／２番目となる。
また、くし形電極６ｂに端部から順番にナンバリングを
施したときの浮き電極指の番号をＮとし、これを中央の
電極指の番号（Ｎ’＋１）／２で除して基準化数Ｎ／
（（Ｎ’＋１）／２）とする。The feature of the IDT according to the present invention is that the central IDT
6, more specifically, when the electrode fingers of the ground-side comb-shaped electrode 6b are arranged symmetrically from the center of the IDT and numbered sequentially from both sides as shown in FIG. The third electrode finger in the figure is a floating electrode finger that is not connected to the terminal side or the ground side. A part (left half from the center) of a plan view of the electrode configuration of the IDT 6 shown in FIG. 1A is enlarged and shown in FIG. FIG.
(B) The third electrode finger from the left of the comb-shaped electrode 6b is replaced with a floating electrode finger.
The third electrode finger from the right end is also replaced with a floating electrode finger on the right side of the center of. Here, when the number of electrode fingers of the comb-shaped electrode 6b is N ′, if the number of electrode fingers of the comb-shaped electrode 6b is odd, the center electrode finger coincides with the center of the IDT 6 and can be counted from the left or right. (N '+ 1) / 2.
The number of the floating electrode finger when the comb-shaped electrode 6b is numbered sequentially from the end is defined as N, and this is divided by the number of the central electrode finger (N '+ 1) / 2 to obtain a normalized number N. /
((N ′ + 1) / 2).
【００１０】くし形電極６ｂにおいて電極指を左右の端
から順に１組だけ浮き電極で置き換えた場合、通過帯域
の低周波側のスプリアスがどのように変化するかを実験
的に調べた。図２はこの時のスプリアスの変化を明らか
にすべく濾波特性を図示したものであり、図２（ａ）の
実線は図７に示した従来のＩＤＴ構成の場合の濾波特性
であり、破線は２番目の電極指を浮き電極で置き換えた
場合の濾波特性を示すものである。図２（ｂ）は図２
（ａ）の矢印２の周波数近傍の実線と破線との差異を拡
大した図がであり、同図の右端の周波数が中心周波数で
ある。図２（ａ）、（ｂ）からも明らかなように通過帯
域より低周波側の一部の帯域のスプリアスのみが抑圧さ
れており、その他の帯域の濾波特性にはほとんど影響を
与えてない。この改善されたスプリアスの帯域の中心周
波数を矢印２で示してある。同様に図２（ｃ）、（ｄ）
の破線は５番目、８番目の電極指を浮き電極指で置き換
えた場合のフィルタの濾波特性であり、矢印５、８は改
善されたスプリアスの帯域の中心周波数を示している。
このように任意のＮ番目の電極指を浮き電極指とした場
合に、スプリアスの改善される周波数帯域の中心をＦと
し、フィルタの通過帯域の中心周波数Ｆ0で基準化した
基準化周波数（Ｆ− Ｆ0）／ Ｆ0と浮き電極の基準化数
Ｎ／（（Ｎ’＋１）／２）との関係を図３に示す。[0010] When the electrode fingers of the comb-shaped electrode 6b are replaced with a set of floating electrodes in order from the left and right ends, how the spurious on the low frequency side of the pass band changes was experimentally examined. FIG. 2 shows the filtering characteristics in order to clarify the change in spurious at this time. The solid line in FIG. 2A shows the filtering characteristics in the case of the conventional IDT configuration shown in FIG. FIG. 14 shows the filtering characteristics when the second electrode finger is replaced with a floating electrode. FIG. 2B shows FIG.
3A is an enlarged view of the difference between the solid line and the broken line near the frequency indicated by the arrow 2 in FIG. 3A, and the rightmost frequency in the figure is the center frequency. As is clear from FIGS. 2A and 2B, only the spurious in a part of the band lower than the pass band is suppressed, and the filtering characteristics in other bands are hardly affected. The center frequency of this improved spurious band is indicated by arrow 2. Similarly, FIGS. 2C and 2D
The broken lines indicate the filtering characteristics of the filter when the fifth and eighth electrode fingers are replaced with floating electrode fingers, and arrows 5 and 8 indicate the center frequency of the improved spurious band.
When an arbitrary N-th electrode finger is used as a floating electrode finger in this manner, the center of the frequency band in which spurious is improved is defined as F, and the reference frequency (F− FIG. 3 shows the relationship between (F0) / F0 and the normalized number N / ((N '+ 1) / 2) of the floating electrodes.
【００１１】図３より明らかなように浮き電極の基準化
数Ｎ／（（Ｎ’＋１）／２）がほぼ０．０５から０．３
５の範囲内ではほぼ次式の直線で近似することができ
る。 （Ｆ− Ｆ0）／ Ｆ0＝０．１３５Ｎ／（（Ｎ’＋１）／
２）−０．０６９ また、基準化数Ｎ／Ｎ’が約０．３５より大きくなる
と、スプリアスが改善される基準化周波数（Ｆ− Ｆ0）
／ Ｆ0はほぼ一定値になることが実験より明らかになっ
た。この図を利用することにより低周波側の任意の周波
数帯におけるスプリアスを改善することが可能となる。As is apparent from FIG. 3, the standardized number N / ((N '+ 1) / 2) of the floating electrodes is approximately 0.05 to 0.3.
In the range of 5, it can be approximated by the following equation. (F−F0) /F0=0.135 N / ((N ′ + 1) /
2) -0.069 Further, when the standardization number N / N 'is larger than about 0.35, the spurious response is improved at the standardized frequency (F-F0).
It has been clarified from experiments that / F0 becomes a substantially constant value. By using this figure, it is possible to improve spurious in an arbitrary frequency band on the low frequency side.
【００１２】ここで本発明を用いた１次−３次縦結合二
重モードＳＡＷフィルタにより所望の周波数帯域におい
てスプリアスを抑圧する場合を考える。例えば（Ｆ0−
７）ＭＨｚから（Ｆ0−２）ＭＨｚの範囲でスプリアス
による減衰量の低減を改善する場合には、図３を参照し
て０＜Ｎ／（（Ｎ’＋１）／２）＜０．１と０．３＜Ｎ
／（（Ｎ’＋１）／２）＜０．３５の二カ所に相当する
電極指を浮き電極指で置き換えればよいことになる。Here, consider a case where spurious is suppressed in a desired frequency band by a first-order / third-order longitudinally-coupled dual-mode SAW filter using the present invention. For example, (F0−
7) In the case where the reduction of the amount of attenuation due to spurious signals is improved in the range from MHz to (F0-2) MHz, 0 <N / ((N '+ 1) / 2) <0.1 with reference to FIG. 0.3 <N
The electrode fingers corresponding to the two positions of /((N′+1)/2)<0.35 may be replaced with floating electrode fingers.
【００１３】他は図７と同じ条件で構成し中央のＩＤＴ
のくし形電極６ｂの左右からＮ＝６と１０の二カ所（対
称構成のため４カ所）の電極指を浮き電極とした二段縦
続接続の１次−３次縦結合二重モードＳＡＷフィルタの
濾波特性を図４に示す。従来の浮き電極を設けないフィ
ルタの濾波特性である図７と比較し、本発明になる浮き
電極を設けたフィルタは図４から明らかなように、所望
のスプリアス帯域において１０〜１５ｄＢの改善がみら
れた。本発明を用いることにより反射器の対数を少なく
することなく、電極膜厚を厚くすることもなく、またＩ
ＤＴに重付けをしなくともスプリアスによる減衰量の低
減を抑制することが可能となった。ただし、これら従来
の手法を不具合が生じない程度に適宜併用すればスプリ
アス抑圧効果が増大することはいうまでもない。The other components are the same as those in FIG.
A two-stage cascaded first- and third-order longitudinally-coupled dual-mode SAW filter in which two electrode fingers N = 6 and 10 (four at the symmetrical configuration) from the left and right sides of the comb-shaped electrode 6b are floating electrodes. FIG. 4 shows the filtering characteristics. As compared with FIG. 7, which is the filtering characteristic of the conventional filter without the floating electrode, the filter with the floating electrode according to the present invention has an improvement of 10 to 15 dB in the desired spurious band, as is apparent from FIG. Was done. By using the present invention, the number of reflectors is not reduced, the electrode film thickness is not increased, and
Even without weighting the DT, it is possible to suppress the reduction in the amount of attenuation due to spurious. However, it is needless to say that the spurious suppression effect is increased if these conventional methods are appropriately used together so as not to cause a problem.
【００１４】上記説明ではＬｉＴａＯ３を用いた例を挙
げたが、ＬｉＮｂＯ３、ＬＢＯ等の圧電性結晶の基板を
用いてもよい。また、上記説明では一対で構成するＩＤ
Ｔのうち一方のＩＤＴを接地する不平衡型ＳＡＷフィル
タを説明したが、一方のＩＤＴを接地しない平衡型ＳＡ
Ｗフィルタに本発明を適用することも可能である。ま
た、中央のＩＤＴ６ｂが奇数の場合を説明したが、本発
明は必ずしもこれに限定するものではなく偶数であって
もよい。In the above description, an example using LiTaO3 is given, but a substrate of a piezoelectric crystal such as LiNbO3 or LBO may be used. Also, in the above description, a pair of IDs
An unbalanced SAW filter in which one IDT of the T is grounded has been described.
The present invention can be applied to a W filter. Although the case where the center IDT 6b is an odd number has been described, the present invention is not necessarily limited to this and may be an even number.
【００１５】[0015]
【発明の効果】本発明は、以上説明したように構成した
ので、従来１次−３次縦結合二重モードＳＡＷフィルタ
において問題であった低周波側のスプリアスを所望の帯
域において減衰させることが可能となった。前記ＳＡＷ
フィルタを携帯電話、コードレス電話等の用いる場合に
所定の不要波を抑制することができ極めて有効な効果が
あがる。As described above, according to the present invention, the spurious component on the low frequency side, which has been a problem in the conventional first-third-order longitudinally-coupled dual-mode SAW filter, can be attenuated in a desired band. It has become possible. The SAW
When a filter is used for a mobile phone, a cordless phone, or the like, a predetermined unnecessary wave can be suppressed, and an extremely effective effect can be obtained.
【図１】（ａ）は本発明に係る１次−３次縦結合二重モ
ードＳＡＷフィルタの一実施例を示す平面図、（ｂ）は
中央ＩＤＴの拡大図である。FIG. 1A is a plan view showing an embodiment of a first-order to third-order longitudinally-coupled dual-mode SAW filter according to the present invention, and FIG. 1B is an enlarged view of a central IDT.
【図２】（ａ）、（ｂ）は２番目の電極指、（ｃ）、
（ｄ）はそれぞれ５、８番目の電極指を浮き電極で置き
換えた時のスプリアスの変化を示す図である。FIGS. 2A and 2B are second electrode fingers, and FIGS.
(D) is a diagram showing a change in spurious when the fifth and eighth electrode fingers are replaced with floating electrodes, respectively.
【図３】電極指の基準化数Ｎ／Ｎ’とスプリアスの低減
される基準化周波数（Ｆ− Ｆ0）／ Ｆ0との関係を表す
図である。FIG. 3 is a diagram showing a relationship between a standardized number N / N ′ of electrode fingers and a standardized frequency (F−F0) / F0 in which spurious is reduced.
【図４】本発明を用いて改善した二段縦続接続１次−３
次縦結合二重モードＳＡＷフィルタの濾波特性図であ
る。FIG. 4 shows a two-stage cascade primary-3 improved using the present invention.
FIG. 8 is a diagram illustrating the filtering characteristics of a next-order longitudinally coupled dual mode SAW filter.
【図５】従来の１次−３次縦結合二重モードＳＡＷフィ
ルタの電極構成を示す平面図である。FIG. 5 is a plan view showing an electrode configuration of a conventional primary-tertiary-order longitudinally coupled dual-mode SAW filter.
【図６】従来の二段縦続接続１次−３次縦結合二重モー
ドＳＡＷフィルタの電極構成を示す平面図である。FIG. 6 is a plan view showing an electrode configuration of a conventional two-stage cascaded primary-tertiary-coupled dual-mode SAW filter.
【図７】従来の二段縦続接続１次−３次縦結合二重モー
ドＳＡＷフィルタの濾波特性を示す図である。FIG. 7 is a diagram showing a filtering characteristic of a conventional two-stage cascade-connected primary-tertiary-order longitudinally coupled dual-mode SAW filter.
１、２、３、４、Ｎ’・・・電極指の番号 ５、５ａ、５ｂ、６、６ａ、６ｂ、７、７ａ、７ｂ・・
・ＩＤＴ ８、９・・・反射器1, 2, 3, 4, N ': electrode finger numbers 5, 5a, 5b, 6, 6a, 6b, 7, 7a, 7b,.
・ IDT 8, 9 ... reflector
Claims (2)
反射器を表面波の伝搬方向に沿って配置した１次−３次
縦結合二重モードＳＡＷフィルタにおいて、中央に位置
する中央ＩＤＴの中心軸を基準としてほぼ対称に位置す
る接地側電極指の少なくとも１組を浮き電極指に置き換
えることを特徴とする二重モードＳＡＷフィルタの構
造。1. A first-third-order longitudinally-coupled dual-mode SAW filter in which three IDTs are arranged on a piezoelectric substrate and reflectors are arranged on both sides of the IDTs along the propagation direction of the surface acoustic wave. Characterized in that at least one pair of ground-side electrode fingers that are located substantially symmetrically with respect to the center axis of the above is replaced with a floating electrode finger.
Ｎ’、浮き電極に置き換えた前記接地側電極指の中央Ｉ
ＤＴ端部からのナンバリングをＮ、フィルタ通過域の中
心周波数をＦ０としたとき、 （Ｆ− Ｆ0）／ Ｆ0＝０．１３５Ｎ／（（Ｎ’＋１）／
２）−０．０６９ の式を満たす周波数Ｆ近傍において、スプリアスを抑圧
することを特徴とする請求項１記載の二重モードＳＡＷ
フィルタの構造。2. The number of ground-side electrode fingers of the central IDT is N ′, and the center I of the ground-side electrode fingers is replaced by floating electrodes.
When the numbering from the DT end is N and the center frequency of the filter passband is F0, (F−F0) /F0=0.135N / ((N ′ + 1) /
2) The dual mode SAW according to claim 1, wherein spurious is suppressed in the vicinity of a frequency F which satisfies -0.069.
The structure of the filter.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP30593996A JP3745847B2 (en) | 1996-10-31 | 1996-10-31 | Structure of dual mode SAW filter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP30593996A JP3745847B2 (en) | 1996-10-31 | 1996-10-31 | Structure of dual mode SAW filter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH10135780A true JPH10135780A (en) | 1998-05-22 |
| JP3745847B2 JP3745847B2 (en) | 2006-02-15 |
Family
ID=17951124
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP30593996A Expired - Fee Related JP3745847B2 (en) | 1996-10-31 | 1996-10-31 | Structure of dual mode SAW filter |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3745847B2 (en) |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2002353777A (en) * | 2001-05-29 | 2002-12-06 | Toyo Commun Equip Co Ltd | Surface acoustic wave filter |
| US6753641B2 (en) | 2001-03-01 | 2004-06-22 | Murata Manufacturing Co., Ltd. | Surface acoustic wave device and communication device |
| US6768397B2 (en) | 2000-11-29 | 2004-07-27 | Murata Manufacturing Co., Ltd. | Surface acoustic wave filter with balanced and unbalanced terminals |
| US6828879B2 (en) * | 2001-02-16 | 2004-12-07 | Sanyo Electric Co., Ltd. | Longitudinal coupled multiple mode surface acoustic wave filter |
| JP2006101550A (en) * | 2005-12-05 | 2006-04-13 | Fujitsu Media Device Kk | Surface acoustic wave device, communication apparatus using the same, and antenna duplexer |
| WO2007040052A1 (en) * | 2005-10-03 | 2007-04-12 | Murata Manufacturing Co., Ltd. | Elastic wave filter device and duplexer |
| JP2008028824A (en) * | 2006-07-24 | 2008-02-07 | Kyocera Corp | Surface acoustic wave device and communication device |
| JP2008028825A (en) * | 2006-07-24 | 2008-02-07 | Kyocera Corp | Surface acoustic wave device and communication device |
| US7518471B2 (en) * | 2005-04-08 | 2009-04-14 | Epson Toyocom Corporation | Surface acoustic wave filter utilizing a floating electrode |
-
1996
- 1996-10-31 JP JP30593996A patent/JP3745847B2/en not_active Expired - Fee Related
Cited By (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6768397B2 (en) | 2000-11-29 | 2004-07-27 | Murata Manufacturing Co., Ltd. | Surface acoustic wave filter with balanced and unbalanced terminals |
| US6828879B2 (en) * | 2001-02-16 | 2004-12-07 | Sanyo Electric Co., Ltd. | Longitudinal coupled multiple mode surface acoustic wave filter |
| KR100600481B1 (en) * | 2001-03-01 | 2006-07-13 | 가부시키가이샤 무라타 세이사쿠쇼 | Surface acoustic wave device and communication device |
| US6753641B2 (en) | 2001-03-01 | 2004-06-22 | Murata Manufacturing Co., Ltd. | Surface acoustic wave device and communication device |
| JP2002353777A (en) * | 2001-05-29 | 2002-12-06 | Toyo Commun Equip Co Ltd | Surface acoustic wave filter |
| US7518471B2 (en) * | 2005-04-08 | 2009-04-14 | Epson Toyocom Corporation | Surface acoustic wave filter utilizing a floating electrode |
| WO2007040052A1 (en) * | 2005-10-03 | 2007-04-12 | Murata Manufacturing Co., Ltd. | Elastic wave filter device and duplexer |
| JPWO2007040052A1 (en) * | 2005-10-03 | 2009-04-16 | 株式会社村田製作所 | Elastic wave filter device and duplexer |
| US7532090B2 (en) | 2005-10-03 | 2009-05-12 | Murata Manufacturing Co., Ltd. | Acoustic wave filter device and duplexer |
| JP4557008B2 (en) * | 2005-10-03 | 2010-10-06 | 株式会社村田製作所 | Elastic wave filter device and duplexer |
| JP2006101550A (en) * | 2005-12-05 | 2006-04-13 | Fujitsu Media Device Kk | Surface acoustic wave device, communication apparatus using the same, and antenna duplexer |
| JP2008028824A (en) * | 2006-07-24 | 2008-02-07 | Kyocera Corp | Surface acoustic wave device and communication device |
| JP2008028825A (en) * | 2006-07-24 | 2008-02-07 | Kyocera Corp | Surface acoustic wave device and communication device |
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| Publication number | Publication date |
|---|---|
| JP3745847B2 (en) | 2006-02-15 |
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