JP2004207902A - Noise filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a downsized inexpensive noise filter capable of preventing resonance of noise and provided with a damping resistor. <P>SOLUTION: An inductor part 2 is formed by providing an inductor transmission line 4 to the front side of an inductor magnetic substance sheet 3. Further, a filter transmission line 11 is provided between two filter magnetic substance sheets 9, 10 and a filter part 8 is formed by sandwiching the two filter magnetic substance sheets 9, 10 by two ground electrodes 12, 13. Then the inductor part 2 and the filter part 8 are stacked to be unified and the transmission lines 4, 11 are connected in series. Thus, the inductor part 2 acts like the damping resistor and the filter part 8 acts like a distributed constant filter. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００３８】
このように、フィルタ用磁性体シートの比透磁率μ_rを４≦μ_r≦３０の範囲内に設定すると共に、Ｌ／√（μ_r−１）≧３ｍｍとなるようにフィルタ用伝送線路の長さ寸法Ｌを設定することによって、遮断周波数の範囲を容易に２００ＭＨｚ≦ｆc≦２ＧＨｚの範囲内に設定することができる。また、ノイズの減衰曲線の傾き（信号の周波数に対する減衰量変化の割合）は、フィルタ用伝送線路の長さ寸法Ｌに比例して大きくなると共に、フィルタ用磁性体シートの比透磁率μ_rに対して√（μ_r−１）に反比例して大きくなる傾向がある。このため、フィルタ用磁性体シートの比透磁率μ_rを４≦μ_r≦３０の範囲に設定し、Ｌ／√（μ_r−１）≧３ｍｍに設定することによって、ノイズの減衰曲線の傾きを例えば２０ｄＢ／ｄｅｃ．以上にすることができ、信号とノイズとの減衰量の差を大きくすることができる。
【００３９】
請求項１２の発明は、前記グランド電極の厚さ寸法は前記フィルタ用伝送線路の厚さ寸法よりも薄く形成したことにある。
【００４０】
これにより、ノイズフィルタ全体の厚さ寸法を薄くすることができ、小型化を図ることができる。また、伝送線路の厚さ寸法をグランド電極に比べて厚くすることができるから、伝送線路の直流抵抗を小さくすることができ、より大きな電流を流すことができる。
【００４１】
請求項１３の発明は、前記インダクタ用磁性体シートおよびフィルタ用磁性体シートは磁性特性をもったセラミックス材料によって形成したことにある。これにより、磁性体シートを重ね合わせた状態で焼成することによってノイズフィルタを形成することができる。この場合、請求項１４の発明のように、各磁性体シートを焼結したフェライトによって形成することが好ましい。
【００４２】
請求項１５の発明は、前記インダクタ用磁性体シートおよびフィルタ用磁性体シートは磁性粉を混入した樹脂材料によって形成したことにある。これにより、各磁性体シートを接着剤を用いて接合することによってノイズフィルタを形成することができ、焼成等の製造工程を省くことができ、生産性を向上させることができる。
【００４３】
【発明の実施の形態】
以下、本発明の実施の形態によるノイズフィルタを、図１ないし図２１に基づき詳細に説明する。
【００４４】
図１ないし図６は第１の実施の形態に係り、１は本実施の形態によるノイズフィルタで、該ノイズフィルタ１は後述するインダクタ部２とフィルタ部８とによって大略構成されている。また、ノイズフィルタ１の遮断周波数ｆcは、例えば２００ＭＨｚから２ＧＨｚ程度の範囲内の値（２００ＭＨｚ≦ｆc≦２ＧＨｚ）に設定されている。
【００４５】
２はダンピング抵抗をなすインダクタ部で、該インダクタ部２は、インダクタ用磁性体シート３と、該インダクタ用磁性体シート３の表面に設けられたインダクタ用伝送線路４とによって構成されている。ここで、インダクタ用磁性体シート３は、略四角形の板状に形成され、例えばフェライト等の磁性特性を有するセラミックス材料によって形成されている。
【００４６】
また、インダクタ用伝送線路４は、例えば銀ペースト、パラジウム等の導電性金属材料によって渦巻き状に形成され、その一端側がインダクタ用磁性体シート３の長さ方向（図１中の左，右方向）一端側に向けて延びると共に、後述の信号用外部電極１６に接続された電極部４Ａをなしている。一方、インダクタ用伝送線路４の他端側は、磁性体シート３，９を貫通して内部に導電性ペースト等が充填されたスルーホール５を通じて後述のフィルタ用伝送線路１１に接続されている。
【００４７】
そして、インダクタ用伝送線路４の特性インピーダンス値は、例えば高周波信号のクロック周波数においてノイズフィルタ１の接続対象となる後述の伝送線路２２の特性インピーダンス値とドライバＩＣ２１の出力インピーダンス値との差の値と同程度の値に設定されている。
【００４８】
なお、インダクタ用伝送線路４のうち自身を跨ぐ途中部位はフェライト等からなる絶縁膜６によって覆われている。これにより、インダクタ用伝送線路４の途中部位が短絡するのを防いでいる。また、インダクタ用磁性体シート３の表面には、インダクタ用伝送線路４を覆う保護膜としての磁性体シート７が設けられている。
【００４９】
８は分布定数型フィルタをなすフィルタ部で、該フィルタ部８は、インダクタ用磁性体シート３の裏面側に積み重ねて設けられた２枚のフィルタ用磁性体シート９，１０と、該磁性体シート９，１０の間に設けられインダクタ用伝送線路４に直列接続された後述のフィルタ用伝送線路１１と、伝送線路１１を含んで磁性体シート９，１０を挟む後述の２枚のグランド電極１２，１３によって構成されている。そして、磁性体シート１０の裏面側には、グランド電極１３を覆う保護膜としての磁性体シート１４が設けられている。
【００５０】
また、フィルタ用磁性体シート９，１０は、インダクタ用磁性体シート３とほぼ同形状をなす略四角形の板状に形成され、例えばフェライト等の磁性特性を有するセラミックス材料によって形成されている。そして、２枚のグランド電極１２，１３に挟まれた磁性体シート９，１０は、その比透磁率μ_rが例えば４から３０程度の範囲内の値（４≦μ_r≦３０）に設定されている。
【００５１】
また、フィルタ用磁性体シート９，１０は、磁性体シート３，７，１４と相互に重なり合って積層した状態でプレスした後に焼成される。これにより、これらの磁性体シート３，７，９，１０，１４は積層体１５を形成している。
【００５２】
なお、磁性体シート９，１０と磁性体シート３，７，１４とは異なる材料を用いる構成としてもよい。即ち、磁性体シート３にはインダクタ部のインダクタンス値を高めるために磁性体シート９，１０よりも比透磁率が大きな材料を用い、磁性体シート７には絶縁性の樹脂皮膜を用い、磁性体シート１４にはアルミナ等の絶縁性のセラミック基板（絶縁性基板）を用いてもよい。但し、製造コストの低減するためには、５枚の磁性体シート３，７，９，１０，１４は全て同じ材料を用いることが好ましい。
【００５３】
１１はフィルタ用磁性体シート９，１０間に配設されたフィルタ用伝送線路で、該フィルタ用伝送線路１１は、例えば銀ペースト、パラジウム等の導電性金属材料によってジグザグ状に蛇行した略帯状に形成され、その全長に亘って一定の幅寸法Ａを有している。そして、フィルタ用伝送線路１１の一端側は、磁性体シート３，９を貫通したスルーホール５を通じてインダクタ用伝送線路４に接続されている。一方、フィルタ用伝送線路１１の他端側は、磁性体シート９，１０の長さ方向他端側に向けて延びると共に、後述の信号用外部電極１７に接続された電極部１１Ａをなしている。そして、フィルタ用伝送線路１１は、磁性体シート９，１０の厚さ方向に対して２枚のグランド電極１２，１３間の略中央に位置し、略全長に亘って２枚のグランド電極１２，１３によって覆われている。
【００５４】
ここで、フィルタ用伝送線路１１の幅寸法をＡ、２枚のグランド電極１２，１３間の距離寸法をＢ、磁性体シート９，１０の透磁率をμ、磁性体シート９，１０の誘電率をεとしたときには、伝送線路１１の特性インピーダンスＷは以下の数２の式に示す値となる。
【００５５】
【数２】

【００５６】
また、伝送線路１１の長さ寸法Ｌ（全長）は、磁性体シート９，１０の比透磁率μ_rに対して例えば以下の数３の式を満たす値に設定されている。
【００５７】
【数３】

【００５８】
なお、小型のチップ部品によってノイズフィルタ１を構成する場合には、伝送線路の長さ寸法Ｌは、例えば１００ｍｍ以下である必要がある。一方、磁性体シート９，１０の比透磁率μ_rは４≦μ_r≦３０に設定されている。このため、Ｌ／√（μ_r−１）の値は、以下の数４の式に示すように３ｍｍ以上かつ２０ｍｍ以下であることが好ましい。
【００５９】
【数４】

【００６０】
１２，１３は磁性体シート９の表面と磁性体シート１０の裏面とにそれぞれ設けられた２枚のグランド電極で、これらのグランド電極１２，１３は、フィルタ用磁性体シート９，１０を上，下方向（厚さ方向）から挟むものである。また、各グランド電極１２，１３は、例えば銀ペースト、パラジウム等の導電性金属材料を用いて略四角形の平板状に形成され、磁性体シート９，１０を略全面に亘って覆っている。さらに、グランド電極１２，１３のうち略四角状をなす磁性体シート９，１０の長さ方向（図２中の左，右方向）中間位置には、幅方向（図２中の前，後方向）両端側に向けて舌状に突出して延びる電極部１２Ａ，１３Ａがそれぞれ設けられ、該電極部１２Ａ，１３Ａは後述のグランド用外部電極１８に接続されている。
【００６１】
そして、グランド電極１２は、フィルタ用磁性体シート９とインダクタ用磁性体シート３との間に挟まれた状態でフィルタ用磁性体シート９の表面に配設されている。一方、グランド電極１３は、フィルタ用磁性体シート１０の裏面に配設されると共に、保護膜としての磁性体シート１４によって覆われている。
【００６２】
１６，１７は積層体１５（磁性体シート３，７，９，１０，１４）の長さ方向両端側にそれぞれ設けられた第１，第２の信号用外部電極で、該各信号用外部電極１６，１７は、積層体１５の端面を覆うと共に、その表面、裏面および側面をも筒状に覆っている。また、信号用外部電極１６，１７は、例えば積層体１５の両端側に導電性金属材料を塗布した後に、この導電性金属材料を焼き付けることによって固定されている。そして、信号用外部電極１６はインダクタ用伝送線路４の電極部４Ａに接続され、信号用外部電極１７はフィルタ用伝送線路１１の電極部１１Ａに接続されている。
【００６３】
１８は積層体１５の長さ方向中間位置で幅方向の両端側にそれぞれ設けられたグランド用外部電極で、該グランド用外部電極１８は、略コ字状をなし、積層体１５の側面に厚さ方向に沿って帯状に延びると共に、その一部が積層体１５の表面と裏面とに延伸している。そして、グランド用外部電極１８は、例えば積層体１５の側面側に導電性金属材料を塗布した状態で焼き付けることによって固定され、グランド電極１２，１３の電極部１２Ａ，１３Ａにそれぞれ接続されている。
【００６４】
本実施の形態によるノイズフィルタ１は上述の如く構成されるものであり、次にその作動について図１ないし図８を参照しつつ説明する。
【００６５】
まず、図７に示すように、例えばドライバＩＣ２１と伝送線路２２を通じてレシーバＩＣ２３が接続された回路に対して、ドライバＩＣ２１と伝送線路２２との間にノイズフィルタ１を接続する。このとき、インダクタ部２に接続された信号用外部電極１６をドライバＩＣ２１側に接続し、フィルタ部８に接続された信号用外部電極１７を伝送線路２２側に接続すると共に、グランド用外部電極１８をグランド端子に接続する。これにより、ドライバＩＣ２１から出力された信号は、インダクタ部２のインダクタ用伝送線路４およびフィルタ部８のフィルタ用伝送線路１１を通じて伝送線路２２に伝達されると共に、グランド電極１２，１３はグランド電位に保持される。
【００６６】
ここで、インダクタ用伝送線路４のインダクタンスによってインダクタ部２のインピーダンスが生じるから、インダクタ部２をダンピング抵抗として機能させることができ、ドライバＩＣ２１の出力抵抗が低いときでもフィルタ部８に向けて確実に信号を伝達することができる。
【００６７】
また、フィルタ部８は図８に示すように分布定数型のフィルタを構成すると共に、磁性体シート９，１０を構成するフェライト等の磁性材料はフィルタ用伝送線路１１を通過する信号の周波数が高くなるに従って信号の熱損失が増大する傾向がある。このため、このような熱損失を用いることによって低域通過型フィルタを構成することができるから、伝送線路１１は、例えば２００ＭＨｚから２ＧＨｚ程度に設定された遮断周波数ｆcよりも低い周波数（１００ＭＨｚ〜１ＧＨｚ程度）の信号を通過させ、これよりも高い周波数の信号をノイズとして減衰し、抑制することができる。
【００６８】
また、伝送線路１１の幅寸法Ａ、磁性体シート９，１０の厚さ寸法（グランド電極１２，１３間の距離寸法Ｂ）を適宜設定することによってフィルタ部８の特性インピーダンスＷを設定することができる。さらに、磁性材料の比誘電率は信号の周波数に関係なくほぼ一定値となるから、特性インピーダンスＷを信号の周波数に依らずほぼ一定値に保持することができる。このため、ノイズフィルタ１に接続される回路に対して、ほぼ全ての周波数領域についてインピーダンス整合を取ることができ、ノイズフィルタ１の反射損失を低下させ、共振によるノイズの増大を防止することができる。
【００６９】
さらに、２枚の磁性体シート９，１０間に伝送線路１１を配設すると共に、当該２枚の磁性体シート９，１０を２枚のグランド電極１２，１３によって挟む構成としたから、２枚のグランド電極１２，１３によって磁性体シート９，１０間に位置する伝送線路１１をその全長に亘って覆うことができる。このため、伝送線路１１の全長に亘って特性インピーダンスＷを一定値に設定できるから、伝送線路１１の途中でノイズに反射が生じることがなく、ノイズの共振を抑制することができる。また、伝送線路１１を通過する信号をグランド電極１２，１３間に閉じ込めることができ、通過帯域での信号の減衰を防止できると共に、外部からの伝送線路１１中にノイズが混入するのを防ぐことができ、信号を確実に伝達することができる。
【００７０】
なお、ノイズフィルタ１の遮断周波数ｆcは、磁性体シート９，１０の磁性材料の組成（磁性体シート９，１０の比透磁率μ_r）および伝送線路１１の長さ寸法Ｌを調整することによって適宜設定できるものである。
【００７１】
そこで、次に磁性体シート９，１０の比透磁率μ_rおよび伝送線路１１の長さ寸法Ｌに対する遮断周波数ｆcの関係について、図９ないし図１４を参照しつつ検討する。
【００７２】
まず、磁性体シート９，１０の比透磁率μ_rを一定の値として例えば１０とし（μ_r＝１０）、伝送線路１１の長さ寸法Ｌを５ｍｍ、１０ｍｍ、２０ｍｍ、５０ｍｍにそれぞれ設定し、フィルタ部８のシミュレーションを行った。この結果、図９に示すように４種類の伝送線路１１の長さ寸法Ｌに対応して、４本の減衰曲線を得た。
【００７３】
図９の結果より、伝送線路１１の長さ寸法Ｌが長くなるに従って、遮断周波数ｆc（減衰量が−３ｄＢとなる周波数）は低下すると共に、例えば減衰量が−１０ｄＢ付近での減衰曲線の傾き（周波数変化に対する減衰量変化の割合）は増加することが分かる。
【００７４】
一方、伝送線路１１の長さ寸法Ｌを一定の値として例えば５０ｍｍとし（Ｌ＝５０ｍｍ）、磁性体シート９，１０の比透磁率μ_rを３，５，１０，２０，３０にそれぞれ設定し、フィルタ部８のシミュレーションを行った。この結果、図１０に示すように５種類の比透磁率μ_rに対応して、５本の減衰曲線を得た。
【００７５】
図１０の結果より、比透磁率μ_rが大きくなるに従って、遮断周波数ｆcは低下するものの、例えば減衰量が−１０ｄＢ付近での減衰曲線の傾きは減少することが分かる。
【００７６】
これらの特性を本願発明者等が鋭意検討した結果、伝送線路１１の長さ寸法Ｌと磁性体シート９，１０の比透磁率μ_rとに基づいて以下の数５の式によって定まる定数Ｃ［ｍｍ］が同一となる場合に、長さ寸法Ｌ、比透磁率μ_rが異なるときであっても、減衰曲線の形状（傾き）はほぼ同一となることが分かった。
【００７７】
【数５】

【００７８】
例えば、図１１は、定数Ｃを一定の値として例えば２０ｍｍとし（Ｃ＝２０ｍｍ）、磁性体シート９，１０の比透磁率μ_rを３，５，１０，２０，３０にそれぞれ設定すると共に、伝送線路１１の長さ寸法Ｌを３５ｍｍ、４５ｍｍ、６３ｍｍ、８９ｍｍ、１０９ｍｍにそれぞれ設定し、シミュレーションを行った場合の減衰曲線を示している。
【００７９】
また、図１２は、定数Ｃを一定の値として例えば３ｍｍとし（Ｃ＝３ｍｍ）、磁性体シート９，１０の比透磁率μ_rを３，５，１０，２０，３０にそれぞれ設定すると共に、伝送線路１１の長さ寸法Ｌを５．１９ｍｍ、６．７２ｍｍ、９．４８ｍｍ、１３．４ｍｍ、１６．４ｍｍにそれぞれ設定し、シミュレーションを行った場合の減衰曲線を示している。
【００８０】
このように、定数Ｃが同一となる場合には、比透磁率μ_rが大きくなるに従って、遮断周波数ｆcは低下するものの、長さ寸法Ｌ、比透磁率μ_rが異なるときでも、減衰曲線の形状（傾き）はほぼ同一となる。また、定数Ｃは大きくなるに従って、減衰曲線の傾きは大きくなる。
【００８１】
そこで、定数Ｃと減衰量が−１０ｄＢ付近での減衰曲線の傾きとの関係を検討したところ、図１１に示す結果を得た。ここで、一般にノイズ対策に用いられるバイパスコンデンサの減衰曲線の傾きは２０ｄＢ／ｄｅｃ．であり、ノイズ対策部品として用いるにはこれ以上の傾きを有していることが望ましい。図１１の結果より、定数Ｃが３ｍｍ以上であれば、減衰曲線の傾きが２０ｄＢ／ｄｅｃ．以上となり、ノイズ対策部品として優れた効果を発揮することが分かる。
【００８２】
また、図１１および図１２の結果より、比透磁率μ_rが同じ値となる場合には、定数Ｃが小さくなるに従って、遮断周波数ｆc（減衰量が−３ｄＢとなる周波数）が高くなることが分かる。このため、フィルタ部８の最高の遮断周波数ｆcを検討するために、定数Ｃを３ｍｍとし（Ｃ＝３ｍｍ）、比透磁率μ_rと遮断周波数ｆcとの関係を検討した。この結果を図１４に示す。
【００８３】
ここで、近年は、デジタル機器同士で情報伝達を行う手段として無線ＬＡＮが普及し始めており、この無線ＬＡＮには例えば２．４５ＧＨｚおよび５ＧＨｚ程度の高周波の信号が用いられている。このため、これらの高周波の信号に対してデジタル機器内の低周波（数百ＭＨｚ程度）の信号を保護するためには、遮断周波数が２ＧＨｚ以下であるノイズフィルタが必要となっている。そこで、図１４の結果を検討すると、遮断周波数ｆcを２ＧＨｚに設定するためには、比透磁率μ_rを４程度に設定すればよいことが分かる。
【００８４】
なお、数５の式によれば、定数Ｃは√（μ_r−１）に反比例しているから、伝送線路１１の長さ寸法Ｌが一定であれば、比透磁率μ_rは小さい値に設定した方が、定数Ｃを大きくして減衰曲線の傾きを大きくすることができる。また、定数Ｃが一定であれば、比透磁率μ_rは小さい値に設定した方が、伝送線路１１の長さ寸法Ｌを短くすることができ、ノイズフィルタ１を小型化することができる。
【００８５】
従って、比透磁率μ_rはできるだけ小さい値として４程度に設定することが望ましい。但し、図１４の結果によれば、定数Ｃが最小値である３ｍｍとしたとき（Ｃ＝３ｍｍ）に、比透磁率μ_rは３０程度に設定しても、遮断周波数ｆcをデジタル機器等で必要となる２００ＭＨｚ程度に設定することができる。このため、比透磁率μ_rは、４以上かつ３０以下の範囲内（４≦μ_r≦３０）に設定することが好ましい。
【００８６】
また、伝送線路１１の長さ寸法Ｌは、長くなるほど定数Ｃが増大するから、できるだけ長い値に設定することが好ましい。しかし、長さ寸法Ｌが長くなるに従ってノイズフィルタ１の全体形状が大きくなるから、ノイズフィルタ１を実用的な大きさにするためには、長さ寸法Ｌはおよそ１００ｍｍ以下である必要がある。ここで、比透磁率μ_rの最小値は４だから、定数Ｃの最大値はおよそ２０程度となる。従って、定数Ｃは、３ｍｍ以上かつ２０ｍｍ以下の範囲内（３ｍｍ≦Ｃ≦２０ｍｍ）に設定することが好ましい。
【００８７】
かくして、本実施の形態によれば、ノイズフィルタ１にはインダクタ用磁性体シート３とインダクタ用伝送線路４とからなるインダクタ部２を設けたから、伝送線路４のインピーダンスによってインダクタ部２をダンピング抵抗として機能させることができ、ドライバＩＣ２１の出力抵抗が低いときでもフィルタ部８に向けて確実に信号を伝達することができる。
【００８８】
また、インダクタ部２とフィルタ部８とを一体形成してノイズフィルタ１を構成したから、ダンピング抵抗を別途接続する必要がなく、ダンピング抵抗の組み付けに伴う手間を省くことができる。さらに、インダクタ部２はフィルタ部８と同様に磁性体シート３と伝送線路４とによって構成したから、フィルタ部８と同様の製造工程を付加することによって、容易にインダクタ部２を形成することができる。このため、ダンピング抵抗とノイズフィルタとを別途製造した場合に比べて、製造コストを低減することができる。
【００８９】
また、インダクタ用伝送線路４のインピーダンス値は、信号周波数において接続対象となる伝送線路２２の特性インピーダンス値とドライバＩＣ２１の出力インピーダンス値との差の値と同程度の値に設定したから、これらの伝送線路４，２２間でインピーダンス整合を取ることができ、高周波信号の反射を小さくすることができる。
【００９０】
さらに、インダクタ部２の伝送線路４を渦巻き状に形成したから、伝送線路４によって形成される磁束を相互に足し合わせてインダクタンスを大きくすることができ、インダクタ部２のインピーダンスを高めることができる。
【００９１】
また、フィルタ部８では２枚のフィルタ用磁性体シート９，１０間にフィルタ用伝送線路１１と配設すると共に、これらの磁性体シート９，１０を２枚のグランド電極１２，１３によって覆う構成としたから、磁性体シート９，１０を構成する磁性材料の熱損失を用いることによってノイズを抑制することができる。また、伝送線路１１の特性インピーダンスＷを信号の周波数に依らずほぼ一定値に保持することができるから、外部の回路とのインピーダンス整合を容易に取ることができる。このため、ノイズフィルタ１の反射損失を低下させることができ、共振によるノイズの増大を防止することができる。
【００９２】
また、フィルタ部８の２枚のグランド電極１２，１３によって磁性体シート９，１０間に位置する伝送線路１１をその全長に亘って覆うことができるから、伝送線路１１の全長に亘って特性インピーダンスＷを一定値に設定することができ、伝送線路１１の途中でノイズが反射することがないのに加え、伝送線路１１を通過する信号をグランド電極１２，１３間に閉じ込めることができる。このため、通過帯域での信号の減衰を防止できると共に、外部からの伝送線路１１中にノイズが混入するのを防ぐことができ、信号を確実に伝達することができる。
【００９３】
さらに、磁性体シート３，９，１０等は略四角状に形成し、該磁性体シート３，９，１０の長さ方向両端側には伝送線路４，１１にそれぞれ接続された信号用外部電極１６，１７を設け、該磁性体シート３，９，１０の長さ方向中間位置にはグランド電極１２，１３に接続されたグランド用外部電極１８を設ける構成としたから、直線状に延びる配線の途中に磁性体シート３，９，１０の長さ方向両端側に位置する信号用外部電極１６，１７を容易に接続することができる。また、磁性体シート３，９，１０の長さ方向中間位置に設けられたグランド用外部電極１８も配線の周辺に設けられたグランド端子に容易に接続することができるから、ノイズフィルタ１の組付け性を向上することができる。
【００９４】
また、磁性体シート９，１０の比透磁率μ_rを４≦μ_r≦３０の範囲内に設定すると共に、定数Ｃが３ｍｍ以上（Ｃ≧３ｍｍ）となるように、伝送線路１１の長さ寸法Ｌを設定したから、遮断周波数ｆcの範囲を容易に実用的な周波数帯である２００ＭＨｚ≦ｆc≦２ＧＨｚの範囲内に設定することができる。さらに、ノイズの減衰曲線の傾きは、伝送線路１１の長さ寸法Ｌに比例して大きくなると共に、√（μ_r−１）に反比例して大きくなる傾向がある。このため、磁性体シート９，１０の比透磁率μ_rを４≦μ_r≦３０の範囲に設定し、定数Ｃを３ｍｍ以上に設定することによって、ノイズの減衰曲線の傾きを例えば２０ｄＢ／ｄｅｃ．以上にすることができる。この結果、信号とノイズとの減衰量の差を大きくすることができるから、信号は減衰させずに通過させることができると共に、ノイズを確実に減衰させることができる。
【００９５】
さらに、フィルタ用伝送線路１１は蛇行したジグザグ状に形成したから、伝送線路１１を直線状に形成した場合に比べて、その長さ寸法Ｌを増加させることができ、ノイズの減衰量を増加させることができる。
【００９６】
次に、図１５ないし図１８は本発明の第２の実施の形態によるノイズフィルタを示し、本実施の形態によるノイズフィルタの特徴は、インダクタ部を複数枚のインダクタ用磁性体シート間に設けられた複数層のインダクタ用伝送線路を直列接続することによって構成し、フィルタ部を複数枚のフィルタ用磁性体シート間にフィルタ用伝送線路とグランド電極とを交互に積み重ね、複数層のフィルタ用伝送線路を直列接続する構成としたことにある。
【００９７】
３１は本実施の形態によるノイズフィルタで、該ノイズフィルタ３１は後述するインダクタ部３２とフィルタ部４６とによって大略構成されている。
【００９８】
３２はダンピング抵抗をなすインダクタ部で、該インダクタ部３２は、例えば４枚のインダクタ用磁性体シート３３〜３６と、該インダクタ用磁性体シート３３〜３６の表面にそれぞれ設けられた後述のインダクタ用伝送線路３７〜４０とによって構成されている。そして、インダクタ用磁性体シート３３〜３６は、略四角形の板状に形成され、例えばフェライト等の磁性特性を有するセラミックス材料によって形成されている。
【００９９】
３７〜４０は磁性体シート３３〜３６の表面にそれぞれ配設された合計４層のインダクタ用伝送線路で、該各伝送線路３７〜４０は、導電性金属材料によって折返し部を有する略コ字状または円弧状をなして形成されている。
【０１００】
ここで、伝送線路３７の一端側は、インダクタ用磁性体シート３３の一端側に向けて延びると共に、後述の信号用外部電極５９に接続された電極部３７Ａをなしている。一方、伝送線路３７の他端側は、磁性体シート３３を貫通して内部に導電性ペースト等が充填されたスルーホール４１を通じて伝送線路３８の一端側に接続されている。また、伝送線路３８の他端側は磁性体シート３４を貫通するスルーホール４２を通じて伝送線路３９の一端側に接続され、伝送線路３９の他端側は磁性体シート３５を貫通するスルーホール４３を通じて伝送線路４０の一端側に接続されている。さらに、伝送線路４０の他端側は磁性体シート３６，４７を貫通するスルーホール４４を通じて後述のフィルタ用伝送線路５１の一端側に接続されている。
【０１０１】
これにより、伝送線路３７〜４０は、互いに直列接続され、磁性体シート３３〜３６の厚さ方向に対して略四角形または円形の開口を有する枠型のコイル状（螺旋状）をなしている。
【０１０２】
また、インダクタ用伝送線路３７〜４０のインピーダンス値は、例えば高周波信号のクロック周波数においてノイズフィルタ１の接続対象となる伝送線路の特性インピーダンス値とドライバＩＣの出力インピーダンス値との差の値と同程度の値に設定されている。さらに、インダクタ用磁性体シート３３の表面には、インダクタ用伝送線路３７を覆う保護膜としての磁性体シート４５が設けられている。
【０１０３】
４６は分布定数型フィルタをなすフィルタ部で、該フィルタ部４６は、最裏面側のインダクタ用磁性体シート３６に対してその裏面に積み重ねて設けられた４枚のフィルタ用磁性体シート４７〜５０と、磁性体シート４７，４８間と磁性体シート４９，５０間にそれぞれ設けられ互いに直列接続された後述のフィルタ用伝送線路５１，５２と、磁性体シート４７の表面、磁性体シート４８，４９間、磁性体シート５０の裏面にそれぞれ設けられた後述する３枚のグランド電極５３〜５５によって構成されている。
【０１０４】
これにより、最表面層と最裏面層とにグランド電極５３，５５が配置される状態で磁性体シート４７〜５０間には伝送線路５１，５２とグランド電極５４とが交互に積み重ねられている。また、磁性体シート５０の裏面側には、グランド電極５５を覆う保護膜としての磁性体シート５６が設けられている。
【０１０５】
そして、フィルタ用磁性体シート４７〜５０は、グランド電極５３〜５５に挟まれると共に、インダクタ用磁性体シート３３〜３６とほぼ同形状の略四角形の板状をなし、第１の実施の形態による磁性体シート９，１０とほぼ同様のフェライト等の磁性特性を有するセラミックス材料によって形成されている。
【０１０６】
また、フィルタ用磁性体シート４７〜５０は、磁性体シート３３〜３６，４５，５６と相互に重なり合って積層した状態でプレスした後に焼成される。これにより、これらの磁性体シート３３〜３６，４５，４７〜５０，５６は積層体５７を形成している。
【０１０７】
５１，５２はフィルタ用磁性体シート４７，４８間とフィルタ用磁性体シート４９，５０間にそれぞれ配設されたフィルタ用伝送線路で、該フィルタ用伝送線路５１は、第１の実施の形態による伝送線路１１とほぼ同様に例えば銀ペースト、パラジウム等の導電性金属材料によってジグザグ状に蛇行した略帯状に形成され、その全長に亘って一定の幅寸法を有している。
【０１０８】
そして、フィルタ用伝送線路５１の一端側は、磁性体シート３６，４７を貫通したスルーホール４４を通じてインダクタ用伝送線路４０に接続され、フィルタ用伝送線路５１の他端側は、磁性体シート４８，４９を貫通したスルーホール５８を通じてフィルタ用伝送線路５２の一端側に接続されている。また、フィルタ用伝送線路５２の他端側は、磁性体シート５０の長さ方向他端側に向けて延びると共に、後述の信号用外部電極６０に接続された電極部５２Ａをなしている。
【０１０９】
そして、伝送線路５１，５２の特性インピーダンスは、第１の実施の形態による伝送線路１１と同様に伝送線路５１，５２の幅寸法、隣り合うグランド電極５３〜５５間の距離寸法、磁性体シート４７〜５０の透磁率、誘電率によって決定される。このため、伝送線路５１，５２の幅寸法をほぼ等しい値に設定すると共に、磁性体シート４７〜５０の厚さ寸法をほぼ等しい値に設定することによって、伝送線路５１，５２の全長に亘って特性インピーダンスを一定値に設定することができる。
【０１１０】
５３〜５５は各層の伝送線路５１，５２を挟むように磁性体シート４７〜５０の間にそれぞれ設けられた合計３枚のグランド電極で、グランド電極５３は磁性体シート４７の表面に配置され、グランド電極５４は磁性体シート４８，４９の間に配置されると共に、グランド電極５５は磁性体シート５０の裏面に配置されている。
【０１１１】
そして、グランド電極５３〜５５は、導電性金属材料を用いて略四角形の平板状に形成され、磁性体シート４７〜５０を略全面に亘って覆っている。さらに、グランド電極５３〜５５には第１の実施の形態によるグランド電極１２，１３とほぼ同様に幅方向両端側に向けて突出した電極部５３Ａ〜５５Ａが設けられ、該電極部５３Ａ〜５５Ａは後述のグランド用外部電極６１に接続されている。
【０１１２】
５９，６０は積層体５７（磁性体シート３３〜３６，４５，４７〜５０，５６）の長さ方向両端側にそれぞれ設けられた導電性金属材料からなる第１，第２の信号用外部電極で、該各信号用外部電極５９，６０は、第１の実施の形態による信号用外部電極１６，１７と同様に積層体５７の端面を覆うと共に、その表面、裏面および側面をも筒状に覆っている。そして、信号用外部電極５９はインダクタ用伝送線路３７の電極部３７Ａに接続され、信号用外部電極６０はフィルタ用伝送線路５２の電極部５２Ａに接続されている。
【０１１３】
６１は積層体５７の長さ方向中間位置で幅方向の両端側にそれぞれ設けられた導電性金属材料からなるグランド用外部電極で、該グランド用外部電極６１は、略コ字形状をなし、積層体５７の側面に厚さ方向に沿って帯状に延びると共に、その一部が積層体５７の表面と裏面とに延伸している。そして、グランド用外部電極６１は、グランド電極５３〜５５の電極部５３Ａ〜５５Ａに接続されている。
【０１１４】
かくして、このように構成される本実施の形態でも、前記第１の実施の形態とほぼ同様の作用効果を得ることができるが、特に本実施の形態では、インダクタ部３２を複数層の伝送線路３７〜４０を直列接続することによって構成すると共に、フィルタ部４６を複数層の伝送線路５１，５２を直列接続することによって構成している。このため、インダクタ部３２、フィルタ部４６のインピーダンスを高めることができると共に、フィルタ部４６を通過するノイズに対する熱損失を増大させ、その減衰量を増加させることができる。
【０１１５】
また、伝送線路５１，５２の幅寸法、磁性体シート４７〜５０の厚さ寸法を全てほぼ等しい値に設定することによって、積層された各層の伝送線路５１，５２での特性インピーダンスを相互にほぼ一致させることができるから、伝送線路５１，５２の途中で特性インピーダンスが変化することがなく、外部の回路との間でインピーダンス整合を容易に取ることができる。
【０１１６】
次に、図１９は本発明の第３の実施の形態によるノイズフィルタを示し、本実施の形態によるノイズフィルタの特徴は、インダクタ用磁性体シートの裏面にフィルタ用磁性体シートを設け、該フィルタ用磁性体シートの裏面にフィルタ用伝送線路と設けると共に、インダクタ用磁性体シートとフィルタ用磁性体シートとの間にグランド電極を設けることによってフィルタ部を構成したことにある。なお、本実施の形態では第１の実施の形態と同一の構成要素に同一の符合を付し、その説明を省略するものとする。
【０１１７】
７１は本実施の形態によるフィルタ部で、該フィルタ部７１は、インダクタ用磁性体シート３の裏面側に積み重ねて設けられた１枚のフィルタ用磁性体シート７２と、該磁性体シート７２の裏面に設けられインダクタ用伝送線路４に直列接続された後述のフィルタ用伝送線路７３と、磁性体シート３，７２の間に位置して磁性体シート７２の表面に設けられた後述のグランド電極７４とによって構成されている。そして、磁性体シート７２の裏面側には、グランド電極７４を覆う保護膜としての磁性体シート７５が設けられている。
【０１１８】
また、フィルタ用磁性体シート７２は、インダクタ用磁性体シート３とほぼ同形状をなす略四角形の板状に形成され、例えばフェライト等の磁性特性を有するセラミックス材料によって形成されている。そして、フィルタ用磁性体シート７２は、磁性体シート３，７，７５と相互に重なり合って積層した状態でプレスした後に焼成される。これにより、これらの磁性体シート３，７，７２，７５は積層体７６を形成している。
【０１１９】
７３はフィルタ用磁性体シート７２の裏面に配設されたフィルタ用伝送線路で、該フィルタ用伝送線路７３は、第１の実施の形態による伝送線路１１とほぼ同様に導電性金属材料によってジグザグ状に蛇行した略帯状に形成され、その全長に亘って一定の幅寸法を有している。そして、フィルタ用伝送線路７３の一端側は、磁性体シート３，７２を貫通したスルーホール５を通じてインダクタ用伝送線路４に接続されている。一方、フィルタ用伝送線路７３の他端側は、磁性体シート７２の長さ方向他端側に向けて延びると共に、第２の信号用外部電極(図示せず)に接続された電極部７３Ａをなしている。
【０１２０】
７４は磁性体シート３，７２間に位置して磁性体シート７２の表面に設けられたグランド電極で、該グランド電極７４は、第１の実施の形態によるグランド電極１２等とほぼ同様に導電性金属材料を用いて略四角形の平板状に形成され、磁性体シート７２を略全面に亘って覆っている。また、グランド電極７４には電極部７４Ａが設けられ、該電極部７４Ａはグランド用外部電極(図示せず)に接続されている。
【０１２１】
かくして、本実施の形態では、磁性体シート７２の裏面に伝送線路７３を設けると共に、磁性体シート７２の表面に設けたグランド電極７４によって該伝送線路７３を覆うことによってフィルタ部７１を構成したから、第１の実施の形態と同様に、磁性体シート７２等の熱損失を利用してノイズを抑制することができる。
【０１２２】
また、伝送線路７３の幅寸法、磁性体シート７２の厚さ寸法を適宜設定することによって、ノイズフィルタの特性インピーダンスを設定することができると共に、該特性インピーダンスを信号の周波数に依らずほぼ一定値に保持することができる。このため、ほぼ全ての周波数領域についてノイズフィルタに接続される回路に対するインピーダンス整合を取ることができ、ノイズフィルタの反射損失を低下させることができる。
【０１２３】
さらに、グランド電極７４によって伝送線路７３を全長に亘って覆うから、伝送線路７３の全長に亘って特性インピーダンスを一定値に設定でき、伝送線路７３の途中でノイズが反射するのを防止でき、ノイズの共振を抑制することができる。
【０１２４】
特に、本実施の形態では、１枚のグランド電極７４を用いてフィルタ部７１を構成するから、２枚のグランド電極を用いる場合に比べてフィルタ部７１の構成を簡略化することができ、製造コストを低減することができる。
【０１２５】
なお、前記第１，第３の実施の形態では、１枚の磁性体シート３と１層の伝送線路４とからなるインダクタ部２をフィルタ部８，７１に接続する構成とした。しかし、本発明はこれに限らず、例えば第２の実施の形態のように複数枚の磁性体シート３３〜３６と複数層の伝送線路３７〜４０からなるインダクタ部３２を第１，第３の実施の形態によるフィルタ部８，７１に接続する構成としてもよい。
【０１２６】
また、前記第１の実施の形態では、２枚の磁性体シート９，１０間に伝送線路１１を挟んだ状態でこれらの磁性体シート９，１０を２枚のグランド電極１２，１３で挟むことによってフィルタ部８を構成し、該フィルタ部８をインダクタ部２に接続する構成とした。しかし、本発明はこれに限らず、例えば第２の実施の形態のように複数枚の磁性体シート４７〜５０間に伝送線路５１，５２とグランド電極５３〜５５とを交互の配設したフィルタ部４６を第１の実施の形態によるインダクタ部２に接続する構成としてもよい。
【０１２７】
また、前記各実施の形態では、フィルタ用伝送線路１１，５１，５２，７３は蛇行したジグザグ状に形成するものとしたが、直線状や渦巻き状に形成する構成としてもよく、第２の実施の形態のインダクタ部３２のように複数層に亘ってコイル状（螺旋状）に形成する構成としてもよい。
【０１２８】
また、図２０に示す第１の変形例のようにフィルタ部８′のグランド電極１２′，１３′の厚さ寸法Ｔ1を伝送線路１１′の厚さ寸法Ｔ2よりも薄く形成してもよい。これにより、ノイズフィルタ全体の厚さ寸法を薄くすることができ、小型化を図ることができる。また、伝送線路１１′の厚さ寸法Ｔ2をグランド電極１２′，１３′の厚さ寸法Ｔ1に比べて厚くすることができるから、伝送線路１１′の直流抵抗を小さくすることができ、より大きな電流を流すことができる。
【０１２９】
また、前記各実施の形態では、単一のノイズフィルタ１，３１に単一のインダクタ部２，３２とフィルタ部８，４６，７１を設けるものとしたが、例えば図２１に示す第２の変形例のように、単一のノイズフィルタ３１′にインダクタ部３２′とフィルタ部４６′を複数個ずつ設ける構成としてもよい。
【０１３０】
さらに、前記各実施の形態では、磁性体シート３，９，１０，３３〜３６，４７〜５０，７２をフェライト等のセラミックス材料によって形成し、これらを焼成する構成とした。しかし、本発明はこれに限らず、磁性体シートを樹脂材料にカルボニル鉄等の磁性粉を混入して形成してもよい。これにより、磁性体シートを接着剤を用いて接合することによって、ノイズフィルタを形成することができ、焼成等の製造工程を省くことができ、生産性を向上させることができる。なお、この場合、ノイズフィルタの遮断周波数は混入する磁性粉の組成および樹脂材料と磁性粉との割合および伝送線路の長さ寸法によって設定されるものである。
【０１３１】
【発明の効果】
以上詳述した通り、請求項１の発明によれば、ダンピング抵抗をなすインダクタ部と、該インダクタ部に接続されノイズを除去するフィルタ部とを一体形成する構成としたから、ダンピング抵抗を別途設ける場合に比べて、組付け作業を簡略化できると共に、製造コストを低減することができる。
【０１３２】
また、フィルタ部は、２枚のフィルタ用磁性体シート間にフィルタ用伝送線路を設けると共に、これらの磁性体シートを２枚のグランド電極によって挟む構成としたから、フィルタ用磁性体シートの熱損失を用いることによってノイズを抑制することができる。また、フィルタ用伝送線路の特性インピーダンスを信号の周波数に依らずほぼ一定値に保持することができるから、外部の回路とのインピーダンス整合を容易に取ることができ、ノイズフィルタの反射損失を低下させ、ノイズの増幅を防止することができる。
【０１３３】
さらに、フィルタ部は２枚のフィルタ用磁性体シートを２枚のグランド電極によって挟む構成としたから、フィルタ用伝送線路を通過する信号を２枚のグランド電極間に閉じ込めることができ、通過帯域での信号の減衰を防止できると共に、外部からの伝送線路中にノイズが混入するのを防ぐことができ、信号を確実に伝達することができる。
【０１３４】
請求項２の発明によれば、インダクタ部を複数枚のインダクタ用磁性体シートと複数層のインダクタ用伝送線路とによって構成したから、請求項１の発明による効果に加えて、インダクタ用伝送線路の全長を長くすることができ、インダクタ部のインピーダンスを高めることができる。
【０１３５】
請求項３の発明によれば、フィルタ部を複数枚のフィルタ用磁性体シートの間にフィルタ用伝送線路とグランド電極とを交互に配置して構成したから、フィルタ用伝送線路の全長を長くして、フィルタ用伝送線路を通過するノイズの減衰量を増加させることができる。
【０１３６】
この場合、請求項４の発明のように、フィルタ部に接続されるインダクタ部は複数枚のインダクタ用磁性体シートと複数層のインダクタ用伝送線路とによって構成してもよい。
【０１３７】
請求項５の発明によれば、１枚のフィルタ用磁性体シートを挟んでフィルタ用伝送線路とグランド電極とをそれぞれ設けることによってフィルタ部を構成したから、請求項１の発明による効果に加えて、フィルタ部の構成を簡略化することができ、製造コストを低減することができる。
【０１３８】
この場合、請求項６の発明のように、フィルタ部に接続されるインダクタ部は複数枚のインダクタ用磁性体シートと複数層のインダクタ用伝送線路とによって構成してもよい。
【０１３９】
請求項７の発明によれば、インダクタ用伝送線路のインピーダンス値を信号周波数において接続対象となる伝送線路の特性インピーダンス値とドライバＩＣの出力インピーダンス値との差の値と同程度の値に設定したから、接続対象となる伝送線路とインダクタ用伝送線路との間でインピーダンス整合を取ることができ、伝送すべき高周波信号の反射を小さくして確実に伝搬させることができる。
【０１４０】
請求項８の発明によれば、フィルタ用伝送線路を蛇行したジグザグ状に形成したから、フィルタ用伝送線路を直線状に形成した場合に比べて、その長さ寸法を増加させることができ、ノイズの減衰量を増加させることができる。
【０１４１】
請求項９の発明によれば、フィルタ用伝送線路は渦巻き状に形成したから、フィルタ用伝送線路によって形成される磁束を相互に足し合わせることができ、インダクタンスを大きくすることができると共に、フィルタ部のインピーダンスを高めることができる。
【０１４２】
請求項１０の発明によれば、インダクタ用磁性体シートおよびフィルタ用磁性体シートは略四角状に形成し、これら磁性体シートの長さ方向両端側にはインダクタ用伝送線路とフィルタ用伝送線路とがそれぞれ接続された第１，第２の信号用外部電極を設け、これら磁性体シートの長さ方向中間位置にはグランド電極に接続されたグランド用外部電極を設ける構成としたから、直線状に延びる配線の途中に磁性体シートの長さ方向両端側に位置する信号用外部電極を容易に接続することができる。また、磁性体シートの長さ方向中間位置に設けられたグランド用外部電極も配線の周辺に設けられたグランド端子に容易に接続することができるから、ノイズフィルタの組付け性を向上することができる。
【０１４３】
請求項１１の発明によれば、フィルタ用磁性体シートの比透磁率μ_rを４≦μ_r≦３０の範囲内に設定すると共に、Ｌ／√（μ_r−１）≧３となるようにフィルタ用伝送線路の長さ寸法Ｌを設定したから、遮断周波数の範囲を容易に実用的な周波数帯である２００ＭＨｚ≦ｆc≦２ＧＨｚの範囲内に設定することができる。また、フィルタ用磁性体シートの比透磁率μ_rを４≦μ_r≦３０の範囲に設定し、Ｌ／√（μ_r−１）≧３に設定したから、ノイズの減衰曲線の傾きを例えば２０ｄＢ／ｄｅｃ．以上にすることができ、信号とノイズとの減衰量の差を大きくすることができる。
【０１４４】
請求項１２の発明によれば、グランド電極の厚さ寸法をフィルタ用伝送線路の厚さ寸法よりも薄く形成したから、ノイズフィルタ全体の厚さ寸法を薄くすることができ、小型化を図ることができる。また、フィルタ用伝送線路の厚さ寸法をグランド電極に比べて厚くすることができるから、伝送線路の直流抵抗を小さくすることができ、より大きな電流を流すことができる。
【０１４５】
請求項１３の発明によれば、磁性体シートは磁性特性をもったセラミックス材料によって形成したから、磁性体シートを重ね合わせた状態で焼成することによってノイズフィルタを形成することができる。この場合、請求項１４の発明のように、磁性体シートを焼結したフェライトによって形成することが好ましい。
【０１４６】
請求項１５の発明によれば、磁性体シートは磁性粉を混入した樹脂材料によって形成したから、磁性体シートを接着剤を用いて接合することによって、ノイズフィルタを形成することができ、焼成等の製造工程を省くことができ、生産性を向上させることができる。
【図面の簡単な説明】
【図１】第１の実施の形態によるノイズフィルタを示す斜視図である。
【図２】図１中のノイズフィルタを分解して示す分解斜視図である。
【図３】ノイズフィルタを図１中の矢示III−III方向からみた断面図である。
【図４】ノイズフィルタを図１中の矢示IV−IV方向からみた断面図である。
【図５】フィルタ用伝送線路等を図２中の矢示Ｖ−Ｖ方向からみた平面図である。
【図６】図３中のａ部を拡大して示す要部拡大断面図である。
【図７】図１中のノイズフィルタを伝送線路等に接続した状態を示す回路図である。
【図８】図１中のノイズフィルタを示す等価回路図である。
【図９】磁性体シートの比透磁率μ_rを１０に設定したときの信号の周波数と減衰量との関係を示す特性線図である。
【図１０】フィルタ用伝送線路の長さ寸法Ｌを５０ｍｍに設定したときの信号の周波数と減衰量との関係を示す特性線図である。
【図１１】定数Ｃを２０ｍｍに設定したときの信号の周波数と減衰量との関係を示す特性線図である。
【図１２】定数Ｃを３ｍｍに設定したときの信号の周波数と減衰量との関係を示す特性線図である。
【図１３】定数Ｃと減衰曲線の傾きとの関係を示す特性線図である。
【図１４】遮断周波数ｆcとフィルタ用磁性体シートの比透磁率μ_rとの関係を示す特性線図である。
【図１５】第２の実施の形態によるノイズフィルタを示す斜視図である。
【図１６】図１５中のノイズフィルタを分解して示す分解斜視図である。
【図１７】ノイズフィルタを図１５中の矢示XVII−XVII方向からみた断面図である。
【図１８】ノイズフィルタを図１５中の矢示XVIII−XVIII方向からみた断面図である。
【図１９】第３の実施の形態によるノイズフィルタを分解して示す分解斜視図である。
【図２０】第１の変形例によるノイズフィルタのフィルタ部を拡大して示す図６を同様位置の要部拡大断面図である。
【図２１】第２の変形例によるノイズフィルタを分解して示す分解斜視図である。
【符号の説明】
１，３１，３１′ ノイズフィルタ
２，３２，３２′ インダクタ部
３，３３〜３６，３３′〜３６′ インダクタ用磁性体シート
４，３７〜４０，３７′〜４０′ インダクタ用伝送線路
８，４６，７１，８′，４６′ フィルタ部
９，１０，４７〜５０，７２，４７′〜５０′ フィルタ用磁性体シート
１１，５１，５２，７３，１１′，５１′，５２′ フィルタ用伝送線路
１２，１３，５３〜５５，７４，１２′，１３′，５３′〜５５′ グランド電極
１６，１７，５９，６０ 信号用外部電極
１８，６１ グランド用外部電極[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a noise filter suitable for suppressing electromagnetic noise interference of an electronic device.
[0002]
[Prior art]
2. Description of the Related Art In general, various types of noise filters are used to suppress electromagnetic noise interference of electronic devices. As a conventional noise filter, there is known a filter formed by a lumped constant circuit such as a three-terminal capacitor (for example, see Patent Document 1). In such a noise filter according to the related art, noise is suppressed by using a reflection loss that increases a reflection coefficient at a frequency that becomes noise (noise).
[0003]
Further, as another conventional noise filter, a noise filter in which a circuit including a large number of inductors, capacitors, and the like is formed is also known (for example, see Patent Document 2).
[0004]
[Patent Document 1]
JP-A-10-154632
[Patent Document 2]
JP 2000-348944 A
[0005]
[Problems to be solved by the invention]
By the way, in the above-described prior art, since noise is suppressed by reflection loss, for example, when a noise filter is provided in a line connecting between circuits, a specific frequency between the noise filter and a peripheral circuit is reduced. There has been a problem that noise may resonate, rather amplifying the noise.
[0006]
In particular, in recent years, the signal frequency used for digital devices tends to be higher, and electronic devices having a signal frequency exceeding 100 MHz are increasing. For this reason, a low-pass filter having a cutoff frequency of 200 MHz or more is required. For example, a high-frequency signal having a line length between a noise filter and surrounding components, a line length between a plurality of components, or the like is 200 MHz or more. Is a length dimension that easily resonates. Therefore, a noise filter using return loss as in the related art tends to be difficult to use for electronic devices having a signal frequency exceeding 100 MHz.
[0007]
Further, in another conventional technique, the resonance phenomenon is suppressed by reducing the reflection loss. However, in other conventional noise filters, since a circuit is formed by connecting a large number of inductors, capacitors, and the like, the structure is complicated, miniaturization is difficult, manufacturing costs are increased, and the noise filter is not chip-shaped. Therefore, there is a problem that it is difficult to attach to a printed wiring.
[0008]
Further, when the output resistance of the driver IC connected to the noise filter is low, a damping resistor is separately connected between the noise filter and the driver IC in order to suppress resonance between the driver IC and peripheral circuits. . In this case, it is necessary to prepare two parts, a noise filter and a damping resistor, and to mount each of these two parts. Therefore, the manufacturing cost is easily increased, and the mounting time is increased, and the productivity is increased. There is also a problem that is reduced.
[0009]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the related art, and an object of the present invention is to provide a small and inexpensive noise filter that can prevent noise resonance and has a damping resistor.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problem, the invention according to claim 1 is a noise filter including an inductor unit forming a damping resistor and a filter unit connected to the inductor unit and removing noise, wherein the inductor unit includes: A magnetic sheet for an inductor, and a transmission line for an inductor provided on a surface of the magnetic sheet for an inductor, wherein the filter portion is provided on the back surface of the magnetic sheet for the inductor and overlaps each other. A filter magnetic sheet, a filter transmission line disposed between the two magnetic sheets and connected in series to the inductor transmission line, and a filter transmission line provided on each of the filter magnetic sheets. It is constituted by two ground electrodes sandwiching the two magnetic sheets for a filter including a line.
[0011]
With this configuration, an impedance is generated in the inductor portion by the inductance of the transmission line for the inductor, so that the inductor portion can function as a damping resistor. Resonance can be suppressed.
[0012]
In addition, since the magnetic material constituting the magnetic sheet for the filter increases the heat loss of the signal as the frequency of the signal passing through the transmission line for the filter increases, noise can be suppressed by using such heat loss. Can be.
[0013]
The characteristic impedance of the filter section can be set by appropriately setting the width of the filter transmission line and the thickness of the magnetic sheet. In particular, since the relative permittivity of the magnetic material has a substantially constant value irrespective of the signal frequency, the characteristic impedance can be maintained at a substantially constant value irrespective of the signal frequency. For this reason, impedance matching can be achieved for circuits connected to the noise filter in almost all frequency ranges, and the reflection loss of the noise filter can be reduced.
[0014]
Further, since the filter transmission line is disposed between the two filter magnetic sheets and the two filter magnetic sheets are sandwiched between the two ground electrodes, the two filter magnetic sheets are sandwiched by the ground electrodes. The filter transmission line located between the body sheets can be covered over its entire length. For this reason, the characteristic impedance can be set to a constant value over the entire length of the filter transmission line, so that no noise is reflected in the middle of the filter transmission line, and noise resonance can be suppressed. Further, a signal passing through the transmission line for the filter can be confined between the two ground electrodes, so that attenuation of the signal in the pass band can be prevented and noise is prevented from being mixed into the transmission line for the filter from the outside. Signal can be transmitted reliably.
[0015]
The invention according to claim 2 is a noise filter comprising an inductor portion forming a damping resistor and a filter portion connected to the inductor portion for removing noise, wherein the inductor portion includes a plurality of inductor magnetic materials overlapping each other. And a transmission line for inductors provided on the surface of each of the magnetic sheets for inductors and connected in series with each other, and the filter unit is an inductor on the rearmost surface side of the plurality of magnetic sheets for inductors. Two filter magnetic sheets stacked on a magnetic sheet for use and overlapping each other; a transmission line for the filter disposed between the two magnetic sheets and connected in series to the transmission line for the inductor; The two magnetic sheets for a filter provided on each magnetic sheet for a filter, including the transmission line for the filter. Lies in the configuration by the two ground electrodes sandwiching.
[0016]
This provides substantially the same function and effect as the first aspect of the present invention, and also connects the inductor transmission lines provided in a plurality of layers in series, so that the impedance of the inductor section can be increased.
[0017]
The invention according to claim 3 is a noise filter including an inductor part forming a damping resistor and a filter part connected to the inductor part to remove noise, wherein the inductor part comprises: a magnetic sheet for an inductor; And a transmission line for inductors provided on the surface of the magnetic sheet for the inductor, the filter unit is provided on the back surface of the magnetic sheet for the inductor, and a plurality of magnetic sheets for the filter, which are overlapped with each other, In a state where ground electrodes are arranged on the outermost layer and the outermost layer of each magnetic sheet for filter, a transmission line for filter and a ground electrode are alternately stacked between the magnetic sheets for each filter, and a plurality of layers of filters are provided. A transmission line is connected in series, and one end thereof is connected in series to the inductor transmission line. That.
[0018]
Accordingly, the impedance of the inductor portion functions as a damping resistor, thereby providing a resonance suppressing effect, and transmitting a high-frequency signal to the filter portion reliably. Further, when the high-frequency signal passes through the transmission line for the filter, noise can be suppressed by utilizing the increase in the heat loss of the magnetic sheet for the filter. Furthermore, the characteristic impedance of the filter unit can be set by appropriately setting the width of the filter transmission line and the thickness of the filter magnetic sheet. In particular, since the relative permittivity of the magnetic material is substantially constant regardless of the signal frequency, impedance matching can be achieved between the noise filter and the circuit connected to the noise filter in almost all frequency ranges. Thus, the reflection loss of the noise filter can be reduced.
[0019]
Further, in a state where the ground electrodes are arranged on the outermost surface layer and the outermost back layer of the plurality of overlapping magnetic sheets for filters, the transmission lines for filters and the ground electrodes are alternately stacked between the magnetic sheets for filters. Therefore, the filter transmission line of each layer can be arranged between two filter magnetic sheets, and the filter transmission line of each layer can be covered over the entire length by two ground electrodes. For this reason, a signal passing through the filter transmission line can be confined between the ground electrodes, and signal attenuation in the pass band can be prevented.
[0020]
In addition, since a plurality of overlapping magnetic sheets for a filter have ground electrodes disposed on the outermost surface layer and the outermost surface layer, noise can be prevented from being externally mixed into the transmission line for the filter, and signals can be prevented. It can be transmitted reliably.
[0021]
Further, when the width dimensions of all the filter transmission lines are set to substantially equal values and the thickness dimensions of all the filter magnetic sheets are set to approximately equal values, the characteristics of each layer with respect to the filter transmission lines are set. The impedances can be made to substantially match each other. For this reason, the characteristic impedance can be set to a substantially constant value over the entirety of the filter transmission lines connected in series with each other, so that no noise is reflected in the middle of the filter transmission lines, and the resonance of the noise is suppressed. And impedance matching with an external circuit can be easily achieved.
[0022]
Furthermore, since the filter transmission lines of a plurality of layers are connected in series, the total length of the filter transmission lines can be increased, and the amount of attenuation of noise passing through the filter transmission lines can be increased.
[0023]
The invention according to claim 4 is a noise filter comprising an inductor part forming a damping resistor and a filter part connected to the inductor part for removing noise, wherein the inductor part comprises a plurality of magnetic materials for inductors overlapping each other. And a transmission line for inductors provided on the surface of each of the magnetic sheets for inductors and connected in series with each other, and the filter unit is an inductor on the rearmost surface side of the plurality of magnetic sheets for inductors. A plurality of magnetic sheets for filters which are provided to be stacked on each other and overlap with each other, and a ground electrode is disposed on the outermost surface layer and the outermost surface layer of each of the magnetic sheets for each filter. Filter transmission lines and ground electrodes are alternately stacked between magnetic sheets to form a multi-layer filter transmission. The road as well as connected in series, and configured to be connected in series to the one end the inductor transmission line.
[0024]
Thereby, substantially the same operation and effect as the third aspect of the invention can be obtained. Further, since the transmission lines for inductors provided in a plurality of layers are connected in series, the overall length of the transmission line for inductors can be increased, and the characteristic impedance of the inductor section can be increased.
[0025]
The invention according to claim 5 is a noise filter comprising an inductor section forming a damping resistor and a filter section connected to the inductor section to remove noise, wherein the inductor section includes a magnetic sheet for an inductor, and the inductor. A filter magnetic sheet provided on the back surface of the inductor magnetic sheet; and a filter magnetic sheet provided on the back surface of the inductor magnetic sheet. A filter transmission line provided on the back surface of the sheet and connected in series to the inductor transmission line; and a filter transmission line provided between the filter magnetic sheet and the inductor magnetic sheet over the entire length. And a ground electrode for covering.
[0026]
With this configuration, the impedance of the inductor portion functions as a damping resistor to provide a resonance suppressing effect, and it is possible to reliably transmit a high-frequency signal to the filter portion. The noise of the signal passing through the filter transmission line can be suppressed by utilizing the heat loss. In addition, by appropriately setting the width dimension of the transmission line for the filter and the thickness dimension of the magnetic sheet for the filter, the characteristic impedance of the filter unit can be set, and the characteristic impedance is almost constant regardless of the signal frequency. Can be held to a value. For this reason, impedance matching can be achieved for circuits connected to the noise filter in almost all frequency ranges, and the reflection loss of the noise filter can be reduced. Furthermore, since the filter transmission line is covered over the entire length by the ground electrode, the characteristic impedance can be set to a constant value over the entire length of the filter transmission line, and reflection and resonance of noise can be suppressed.
[0027]
The invention of claim 6 is a noise filter comprising an inductor part forming a damping resistor and a filter part connected to the inductor part for removing noise, wherein the inductor part comprises a plurality of magnetic materials for inductors overlapping each other. And a transmission line for inductors provided on the surface of each of the magnetic sheets for inductors and connected in series with each other, and the filter unit is an inductor on the rearmost surface side of the plurality of magnetic sheets for inductors. A magnetic sheet for a filter provided by being stacked on a magnetic sheet for use in a filter, a transmission line for a filter provided on a back surface of the magnetic sheet for the filter and connected in series to the transmission line for an inductor, and the magnetic sheet for a filter Between the filter and the magnetic sheet for the inductor and covering the transmission line for the filter over the entire length. It lies in the configuration by the cathode electrode.
[0028]
This makes it possible to obtain substantially the same functions and effects as the invention of claim 5, and to connect the inductor transmission lines provided in a plurality of layers in series, so that the characteristic impedance of the inductor section can be increased.
[0029]
In the invention according to claim 7, the impedance value of the transmission line for the inductor is set to a value substantially equal to the difference value between the characteristic impedance value of the transmission line to be connected and the output impedance value of the driver IC at the signal frequency. are doing.
[0030]
Thereby, impedance matching can be achieved between the transmission line to be connected and the transmission line for the inductor, and reflection of a high-frequency signal can be reduced.
[0031]
In the invention of claim 8, the transmission line for the filter is formed in a meandering zigzag shape. This makes it possible to increase the length dimension and increase the amount of noise attenuation as compared with the case where the filter transmission line is formed linearly.
[0032]
According to the ninth aspect, the transmission line for the filter is formed in a spiral shape. Thus, the magnetic fluxes formed by the filter transmission lines are added together, so that the inductance can be increased and the impedance of the filter section can be increased.
[0033]
According to the tenth aspect of the present invention, the magnetic sheet for the inductor and the magnetic sheet for the filter are formed in a rectangular shape, and the first signal connected to the transmission line for the inductor is provided on one end side in the longitudinal direction of the magnetic sheet. The second external electrode for signal connected to the transmission line for the filter is provided on the other end of the magnetic sheet in the longitudinal direction, and the external electrode for the signal is provided at an intermediate position in the longitudinal direction of the magnetic sheet. An external ground electrode connected to the ground electrode is provided.
[0034]
Thus, the two signal external electrodes located at both ends in the length direction of the magnetic sheet can be easily connected to the middle of the linearly extending wiring. In addition, the ground external electrode provided at the intermediate position in the length direction of the magnetic sheet can be easily connected to the ground terminal provided around the wiring. Therefore, it is possible to improve the assemblability of the noise filter.
[0035]
According to the eleventh aspect of the present invention, the cutoff frequency is in a range of 200 MHz to 2 GHz, and the relative magnetic permeability of the magnetic sheet for a filter is set to μ. _r When the length of the filter transmission line is L [mm], 4 ≦ μ _r ≦ 30, L / √ (μ _r -1) is set to ≧ 3 mm.
[0036]
Here, the relative permeability μ _r Is the magnetic permeability μ [H / m] of the magnetic sheet for the filter and the magnetic permeability μ in a vacuum. ₀ [H / m] and a value represented by the following equation (1).
[0037]
(Equation 1)

[0038]
Thus, the relative magnetic permeability μ of the magnetic sheet for filter is _r Is 4 ≦ μ _r ≦ 30 and L / √ (μ _r -1) By setting the length L of the filter transmission line so as to satisfy ≧ 3 mm, the cutoff frequency range can be easily set within the range of 200 MHz ≦ fc ≦ 2 GHz. The slope of the noise attenuation curve (the ratio of the change in the amount of attenuation to the frequency of the signal) increases in proportion to the length L of the transmission line for the filter, and the relative permeability μ of the magnetic sheet for the filter. _r √ (μ _r -1) tends to increase in inverse proportion. Therefore, the relative magnetic permeability μ of the magnetic sheet for the filter is _r Is 4 ≦ μ _r ≦ 30, L / √ (μ _r -1) By setting ≧ 3 mm, the slope of the noise attenuation curve is set to, for example, 20 dB / dec. As described above, the difference between the signal and noise attenuation can be increased.
[0039]
In a twelfth aspect of the present invention, the thickness of the ground electrode is smaller than the thickness of the transmission line for the filter.
[0040]
Thus, the thickness dimension of the entire noise filter can be reduced, and the size can be reduced. Further, since the thickness of the transmission line can be made larger than that of the ground electrode, the DC resistance of the transmission line can be reduced and a larger current can flow.
[0041]
According to a thirteenth aspect of the present invention, the magnetic sheet for inductor and the magnetic sheet for filter are formed of a ceramic material having magnetic properties. This makes it possible to form a noise filter by firing the magnetic sheets in a stacked state. In this case, it is preferable that each magnetic sheet is formed of sintered ferrite.
[0042]
The invention of claim 15 is that the magnetic sheet for inductor and the magnetic sheet for filter are formed of a resin material mixed with magnetic powder. This makes it possible to form a noise filter by joining the respective magnetic sheets using an adhesive, so that manufacturing steps such as firing can be omitted, and productivity can be improved.
[0043]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a noise filter according to an embodiment of the present invention will be described in detail with reference to FIGS.
[0044]
1 to 6 relate to the first embodiment, 1 is a noise filter according to the present embodiment, and the noise filter 1 is generally constituted by an inductor unit 2 and a filter unit 8 described later. Further, the cutoff frequency fc of the noise filter 1 is set to a value (200 MHz ≦ fc ≦ 2 GHz), for example, in a range from about 200 MHz to about 2 GHz.
[0045]
Numeral 2 denotes an inductor part which forms a damping resistance. The inductor part 2 is constituted by a magnetic sheet for inductor 3 and a transmission line 4 for inductor provided on the surface of the magnetic sheet for inductor 3. Here, the inductor magnetic material sheet 3 is formed in a substantially rectangular plate shape, and is formed of, for example, a ceramic material having magnetic characteristics such as ferrite.
[0046]
Further, the transmission line 4 for the inductor is formed in a spiral shape with a conductive metal material such as silver paste or palladium, and one end thereof is in the length direction of the magnetic sheet 3 for the inductor (left and right in FIG. 1). It extends toward one end and forms an electrode portion 4A connected to a signal external electrode 16 described later. On the other hand, the other end side of the transmission line 4 for the inductor is connected to a transmission line 11 for a filter to be described later through a through hole 5 which penetrates the magnetic sheets 3 and 9 and is filled with a conductive paste or the like.
[0047]
The characteristic impedance value of the transmission line 4 for the inductor is, for example, the difference between the characteristic impedance value of the transmission line 22 to be connected to the noise filter 1 and the output impedance value of the driver IC 21 at the clock frequency of the high-frequency signal. It is set to the same value.
[0048]
A part of the transmission line 4 for the inductor that straddles itself is covered with an insulating film 6 made of ferrite or the like. This prevents a short circuit in the middle of the inductor transmission line 4. A magnetic sheet 7 is provided on the surface of the inductor magnetic sheet 3 as a protective film that covers the inductor transmission line 4.
[0049]
Numeral 8 denotes a filter part which forms a distributed constant type filter. The filter part 8 is composed of two magnetic sheets 9 and 10 for filters provided on the back side of the magnetic sheet 3 for inductors. A transmission line 11 for a filter, which will be described later, provided between the transmission lines 9 and 10 and connected in series to the transmission line 4 for an inductor, and two ground electrodes 12 described below that sandwich the magnetic sheets 9 and 10 including the transmission line 11, 13. On the back surface of the magnetic material sheet 10, a magnetic material sheet 14 is provided as a protective film covering the ground electrode 13.
[0050]
The magnetic sheets 9 and 10 for filters are formed in a substantially rectangular plate shape having substantially the same shape as the magnetic sheet 3 for inductors, and are formed of a ceramic material having magnetic characteristics such as ferrite, for example. The magnetic sheets 9 and 10 sandwiched between the two ground electrodes 12 and 13 have their relative magnetic permeability μ. _r Is, for example, a value in the range of about 4 to 30 (4 ≦ μ _r ≦ 30).
[0051]
The magnetic sheets 9 and 10 for filters are fired after being pressed in a state where the magnetic sheets 9 and 10 overlap each other with the magnetic sheets 3, 7 and 14. Thus, these magnetic sheets 3, 7, 9, 10, and 14 form a laminate 15.
[0052]
The magnetic sheets 9, 10 and the magnetic sheets 3, 7, 14 may be made of different materials. That is, a material having a higher relative magnetic permeability than the magnetic sheets 9 and 10 is used for the magnetic sheet 3 in order to increase the inductance value of the inductor portion, and an insulating resin film is used for the magnetic sheet 7. For the sheet 14, an insulating ceramic substrate (insulating substrate) such as alumina may be used. However, in order to reduce the manufacturing cost, it is preferable to use the same material for all the five magnetic sheets 3, 7, 9, 10, and 14.
[0053]
Reference numeral 11 denotes a transmission line for a filter provided between the magnetic sheets 9 and 10 for the filter. It has a constant width A over its entire length. One end of the filter transmission line 11 is connected to the inductor transmission line 4 through the through hole 5 penetrating the magnetic sheets 3 and 9. On the other hand, the other end of the filter transmission line 11 extends toward the other end in the length direction of the magnetic sheets 9 and 10, and forms an electrode portion 11A connected to a signal external electrode 17 described later. . The filter transmission line 11 is located substantially at the center between the two ground electrodes 12, 13 in the thickness direction of the magnetic sheets 9, 10, and extends over substantially the entire length of the two ground electrodes 12, 13. 13.
[0054]
Here, the width dimension of the filter transmission line 11 is A, the distance dimension between the two ground electrodes 12 and 13 is B, the magnetic permeability of the magnetic sheets 9 and 10 is μ, and the dielectric constant of the magnetic sheets 9 and 10 is Is ε, the characteristic impedance W of the transmission line 11 is a value represented by the following equation (2).
[0055]
(Equation 2)

[0056]
The length L (overall length) of the transmission line 11 is determined by the relative permeability μ of the magnetic sheets 9 and 10. _r Is set to a value that satisfies, for example, the following equation (3).
[0057]
[Equation 3]

[0058]
When the noise filter 1 is formed by small chip components, the length L of the transmission line needs to be, for example, 100 mm or less. On the other hand, the relative permeability μ of the magnetic sheets 9 and 10 _r Is 4 ≦ μ _r ≦ 30 is set. Therefore, L / Ｌ (μ _r The value of -1) is preferably not less than 3 mm and not more than 20 mm as shown in the following equation (4).
[0059]
(Equation 4)

[0060]
Reference numerals 12 and 13 denote two ground electrodes provided on the front surface of the magnetic material sheet 9 and the back surface of the magnetic material sheet 10, respectively. It is sandwiched from below (thickness direction). Each of the ground electrodes 12 and 13 is formed in a substantially rectangular flat plate shape using a conductive metal material such as silver paste or palladium, and covers the magnetic sheets 9 and 10 over substantially the entire surface. Further, the substantially square magnetic material sheets 9 and 10 of the ground electrodes 12 and 13 are located at intermediate positions in the length direction (left and right directions in FIG. 2) in the width direction (front and rear directions in FIG. 2). The electrode portions 12A and 13A are provided to extend in a tongue shape toward both end sides, respectively, and the electrode portions 12A and 13A are connected to a ground external electrode 18 described later.
[0061]
The ground electrode 12 is disposed on the surface of the filter magnetic sheet 9 in a state sandwiched between the filter magnetic sheet 9 and the inductor magnetic sheet 3. On the other hand, the ground electrode 13 is arranged on the back surface of the magnetic sheet for filter 10 and is covered with a magnetic sheet 14 as a protective film.
[0062]
Reference numerals 16 and 17 denote first and second signal external electrodes provided on both ends in the longitudinal direction of the laminated body 15 (magnetic sheets 3, 7, 9, 10, and 14), respectively. Reference numerals 16 and 17 cover the end surface of the laminate 15 and also cover the front surface, the back surface, and the side surfaces of the laminate 15 in a cylindrical shape. The signal external electrodes 16 and 17 are fixed by, for example, applying a conductive metal material to both end sides of the laminate 15 and then baking the conductive metal material. The signal external electrode 16 is connected to the electrode portion 4A of the transmission line 4 for the inductor, and the signal external electrode 17 is connected to the electrode portion 11A of the transmission line 11 for the filter.
[0063]
Reference numerals 18 denote external ground electrodes provided at both ends in the width direction at intermediate positions in the length direction of the laminated body 15. The external ground electrodes 18 are substantially U-shaped, and have a thickness on the side surface of the laminated body 15. While extending in a strip shape along the width direction, a part thereof extends to the front surface and the back surface of the laminate 15. The ground external electrode 18 is fixed by, for example, baking while applying a conductive metal material to the side surface of the multilayer body 15, and is connected to the electrode portions 12 A and 13 A of the ground electrodes 12 and 13, respectively.
[0064]
The noise filter 1 according to the present embodiment is configured as described above. Next, the operation thereof will be described with reference to FIGS.
[0065]
First, as shown in FIG. 7, a noise filter 1 is connected between the driver IC 21 and the transmission line 22 for a circuit in which the receiver IC 23 is connected through the driver IC 21 and the transmission line 22, for example. At this time, the signal external electrode 16 connected to the inductor unit 2 is connected to the driver IC 21 side, the signal external electrode 17 connected to the filter unit 8 is connected to the transmission line 22 side, and the ground external electrode 18 is connected. To the ground terminal. Thus, the signal output from the driver IC 21 is transmitted to the transmission line 22 through the inductor transmission line 4 of the inductor unit 2 and the filter transmission line 11 of the filter unit 8, and the ground electrodes 12 and 13 are set to the ground potential. Will be retained.
[0066]
Here, since the inductance of the inductor section 2 is generated by the inductance of the transmission line 4 for the inductor, the inductor section 2 can function as a damping resistor. Signals can be transmitted.
[0067]
The filter section 8 constitutes a distributed constant type filter as shown in FIG. 8, and the magnetic material such as ferrite constituting the magnetic sheets 9 and 10 has a high signal frequency passing through the filter transmission line 11. As a result, the heat loss of the signal tends to increase. For this reason, a low-pass filter can be configured by using such heat loss. Therefore, the transmission line 11 has a frequency (100 MHz to 1 GHz) lower than the cutoff frequency fc set at, for example, 200 MHz to about 2 GHz. ), And a signal having a higher frequency than this signal can be attenuated and suppressed as noise.
[0068]
The characteristic impedance W of the filter unit 8 can be set by appropriately setting the width dimension A of the transmission line 11 and the thickness dimension (distance dimension B between the ground electrodes 12 and 13) of the magnetic sheets 9 and 10. it can. Further, since the relative permittivity of the magnetic material has a substantially constant value irrespective of the signal frequency, the characteristic impedance W can be maintained at a substantially constant value regardless of the signal frequency. Therefore, impedance matching can be achieved in almost all frequency ranges with respect to the circuit connected to the noise filter 1, the reflection loss of the noise filter 1 can be reduced, and an increase in noise due to resonance can be prevented. .
[0069]
Further, the transmission line 11 is disposed between the two magnetic sheets 9 and 10, and the two magnetic sheets 9 and 10 are sandwiched between the two ground electrodes 12 and 13. The transmission line 11 located between the magnetic sheets 9 and 10 can be covered over its entire length by the ground electrodes 12 and 13. For this reason, since the characteristic impedance W can be set to a constant value over the entire length of the transmission line 11, the noise does not reflect in the middle of the transmission line 11, and the resonance of the noise can be suppressed. Further, a signal passing through the transmission line 11 can be confined between the ground electrodes 12 and 13, so that signal attenuation in the pass band can be prevented and noise can be prevented from being mixed into the transmission line 11 from the outside. And the signal can be transmitted reliably.
[0070]
The cutoff frequency fc of the noise filter 1 is determined by the composition of the magnetic material of the magnetic sheets 9 and 10 (the relative magnetic permeability μ of the magnetic sheets 9 and 10). _r ) And the length L of the transmission line 11 can be adjusted as appropriate.
[0071]
Therefore, next, the relative magnetic permeability μ of the magnetic sheets 9 and 10 is shown. _r The relationship between the cutoff frequency fc and the length L of the transmission line 11 will be discussed with reference to FIGS.
[0072]
First, the relative magnetic permeability μ of the magnetic sheets 9 and 10 _r As a constant value, for example, 10 (μ _r = 10), the length L of the transmission line 11 was set to 5 mm, 10 mm, 20 mm, and 50 mm, respectively, and the simulation of the filter unit 8 was performed. As a result, four attenuation curves were obtained corresponding to the lengths L of the four types of transmission lines 11 as shown in FIG.
[0073]
From the results of FIG. 9, as the length L of the transmission line 11 increases, the cutoff frequency fc (the frequency at which the attenuation becomes -3 dB) decreases, and for example, the slope of the attenuation curve when the attenuation is around -10 dB. It can be seen that (the ratio of the attenuation change to the frequency change) increases.
[0074]
On the other hand, the length L of the transmission line 11 is set to a fixed value, for example, 50 mm (L = 50 mm), and the relative permeability μ of the magnetic sheets 9 and 10 is set. _r Were set to 3, 5, 10, 20, and 30, respectively, and the simulation of the filter unit 8 was performed. As a result, as shown in FIG. _r , Five decay curves were obtained.
[0075]
From the results of FIG. 10, the relative magnetic permeability μ _r It can be seen that the cutoff frequency fc decreases as the value increases, but the slope of the attenuation curve decreases, for example, when the attenuation is around -10 dB.
[0076]
As a result of intensive studies of these characteristics by the present inventors, the length L of the transmission line 11 and the relative magnetic permeability μ of the magnetic sheets 9 and 10 were determined. _r When the constant C [mm] determined by the following equation (5) is the same, the length dimension L and the relative magnetic permeability μ _r It was found that the shape (inclination) of the attenuation curve was almost the same even when
[0077]
(Equation 5)

[0078]
For example, FIG. 11 shows that the constant C is set to a constant value, for example, 20 mm (C = 20 mm), and the relative magnetic permeability μ _r Are set to 3, 5, 10, 20, and 30, respectively, and the length dimension L of the transmission line 11 is set to 35 mm, 45 mm, 63 mm, 89 mm, and 109 mm, respectively. I have.
[0079]
FIG. 12 shows that the constant C is set to a constant value of, for example, 3 mm (C = 3 mm), and the relative magnetic permeability μ of the magnetic sheets 9 and 10 is changed. _r Are set to 3, 5, 10, 20, and 30, respectively, and the length L of the transmission line 11 is set to 5.19 mm, 6.72 mm, 9.48 mm, 13.4 mm, and 16.4 mm. 7 shows an attenuation curve in the case where is performed.
[0080]
As described above, when the constant C is the same, the relative permeability μ _r Becomes larger, the cutoff frequency fc decreases, but the length L, the relative magnetic permeability μ _r Are different, the shape (slope) of the attenuation curve is almost the same. The slope of the attenuation curve increases as the constant C increases.
[0081]
Then, when the relationship between the constant C and the slope of the attenuation curve when the attenuation amount was around -10 dB was examined, the result shown in FIG. 11 was obtained. Here, the slope of the attenuation curve of a bypass capacitor generally used for noise suppression is 20 dB / dec. Therefore, it is desirable to have an inclination greater than this for use as a noise suppression component. According to the results of FIG. 11, when the constant C is 3 mm or more, the slope of the attenuation curve is 20 dB / dec. From the above, it can be seen that excellent effects are exhibited as noise suppression components.
[0082]
Further, from the results of FIGS. 11 and 12, the relative magnetic permeability μ _r Have the same value, the cutoff frequency fc (the frequency at which the amount of attenuation is -3 dB) increases as the constant C decreases. For this reason, in order to study the highest cutoff frequency fc of the filter section 8, the constant C is set to 3 mm (C = 3 mm), and the relative magnetic permeability μ _r The relationship between the frequency and the cutoff frequency fc was examined. The result is shown in FIG.
[0083]
In recent years, wireless LANs have begun to spread as means for transmitting information between digital devices, and high-frequency signals of, for example, about 2.45 GHz and 5 GHz are used for the wireless LAN. Therefore, in order to protect low-frequency (about several hundred MHz) signals in digital equipment against these high-frequency signals, a noise filter having a cutoff frequency of 2 GHz or less is required. Therefore, considering the results of FIG. 14, it is found that the relative permeability μ _r Is set to about 4.
[0084]
According to the equation (5), the constant C is √ (μ _r -1), the relative permeability μ is constant if the length L of the transmission line 11 is constant. _r If is set to a small value, the constant C can be increased and the slope of the attenuation curve can be increased. If the constant C is constant, the relative magnetic permeability μ _r When the value of is set to a small value, the length L of the transmission line 11 can be shortened, and the noise filter 1 can be downsized.
[0085]
Therefore, the relative magnetic permeability μ _r Is desirably set to about 4 as a value as small as possible. However, according to the result of FIG. 14, when the constant C is set to the minimum value of 3 mm (C = 3 mm), the relative permeability μ _r Even if is set to about 30, the cut-off frequency fc can be set to about 200 MHz required for digital devices and the like. Therefore, the relative permeability μ _r Is in the range of 4 or more and 30 or less (4 ≦ μ _r ≦ 30).
[0086]
Further, since the constant C increases as the length L of the transmission line 11 increases, it is preferable to set the length L as long as possible. However, since the overall shape of the noise filter 1 increases as the length L increases, the length L needs to be about 100 mm or less in order to make the noise filter 1 practical. Here, relative permeability μ _r Is 4, the maximum value of the constant C is about 20. Therefore, it is preferable that the constant C is set within a range of 3 mm or more and 20 mm or less (3 mm ≦ C ≦ 20 mm).
[0087]
Thus, according to the present embodiment, since the noise filter 1 is provided with the inductor portion 2 including the inductor magnetic sheet 3 and the inductor transmission line 4, the impedance of the transmission line 4 makes the inductor portion 2 a damping resistor. The signal can be reliably transmitted to the filter section 8 even when the output resistance of the driver IC 21 is low.
[0088]
Further, since the noise filter 1 is formed by integrally forming the inductor section 2 and the filter section 8, it is not necessary to separately connect a damping resistor, and the labor involved in assembling the damping resistor can be omitted. Further, since the inductor section 2 is constituted by the magnetic sheet 3 and the transmission line 4 like the filter section 8, the inductor section 2 can be easily formed by adding the same manufacturing process as that of the filter section 8. it can. Therefore, the manufacturing cost can be reduced as compared with a case where the damping resistor and the noise filter are separately manufactured.
[0089]
Further, since the impedance value of the transmission line 4 for the inductor is set to a value substantially equal to the difference between the characteristic impedance value of the transmission line 22 to be connected and the output impedance value of the driver IC 21 at the signal frequency, Impedance matching can be achieved between the transmission lines 4 and 22, and reflection of high-frequency signals can be reduced.
[0090]
Further, since the transmission line 4 of the inductor section 2 is formed in a spiral shape, the magnetic flux formed by the transmission line 4 can be added to each other to increase the inductance, and the impedance of the inductor section 2 can be increased.
[0091]
In the filter section 8, a filter transmission line 11 is disposed between two filter magnetic sheets 9 and 10, and these magnetic sheets 9 and 10 are covered by two ground electrodes 12 and 13. Therefore, noise can be suppressed by using the heat loss of the magnetic material constituting the magnetic material sheets 9 and 10. Further, since the characteristic impedance W of the transmission line 11 can be maintained at a substantially constant value regardless of the frequency of the signal, impedance matching with an external circuit can be easily achieved. Therefore, the reflection loss of the noise filter 1 can be reduced, and an increase in noise due to resonance can be prevented.
[0092]
Further, since the transmission line 11 located between the magnetic sheets 9 and 10 can be covered over the entire length thereof by the two ground electrodes 12 and 13 of the filter section 8, the characteristic impedance is provided over the entire length of the transmission line 11. W can be set to a constant value, so that noise is not reflected in the middle of the transmission line 11 and a signal passing through the transmission line 11 can be confined between the ground electrodes 12 and 13. Therefore, it is possible to prevent the signal from being attenuated in the pass band, to prevent the noise from being mixed into the transmission line 11 from the outside, and to surely transmit the signal.
[0093]
Further, the magnetic sheets 3, 9, 10 and the like are formed in a substantially rectangular shape, and signal external electrodes connected to the transmission lines 4, 11 are provided on both ends in the longitudinal direction of the magnetic sheets 3, 9, 10 respectively. 16 and 17 are provided, and an external ground electrode 18 connected to the ground electrodes 12 and 13 is provided at an intermediate position in the longitudinal direction of the magnetic sheets 3, 9 and 10. The signal external electrodes 16 and 17 located at both ends in the length direction of the magnetic sheets 3, 9 and 10 can be easily connected on the way. In addition, the ground external electrode 18 provided at the intermediate position in the longitudinal direction of the magnetic sheets 3, 9, 10 can be easily connected to the ground terminal provided around the wiring. The attachment property can be improved.
[0094]
The relative magnetic permeability μ of the magnetic sheets 9 and 10 _r Is 4 ≦ μ _r ≦ 30 and the length L of the transmission line 11 is set so that the constant C is 3 mm or more (C ≧ 3 mm). Therefore, the range of the cutoff frequency fc can be easily changed to a practical frequency. The band can be set within the range of 200 MHz ≦ fc ≦ 2 GHz. Further, the slope of the noise attenuation curve increases in proportion to the length L of the transmission line 11 and √ (μ _r -1) tends to increase in inverse proportion. Therefore, the relative magnetic permeability μ of the magnetic sheets 9 and 10 is _r Is 4 ≦ μ _r By setting the constant C to 3 mm or more, the slope of the noise attenuation curve is set to, for example, 20 dB / dec. Or more. As a result, the difference between the attenuation amount of the signal and the noise can be increased, so that the signal can be passed without being attenuated and the noise can be attenuated reliably.
[0095]
Further, since the filter transmission line 11 is formed in a meandering zigzag shape, the length L can be increased as compared with the case where the transmission line 11 is formed in a linear shape, and the amount of noise attenuation is increased. be able to.
[0096]
15 to 18 show a noise filter according to a second embodiment of the present invention. The feature of the noise filter according to the present embodiment is that an inductor portion is provided between a plurality of inductor magnetic sheets. A plurality of layers of the transmission lines for the inductors are connected in series, and the filter section is alternately stacked with the transmission lines for the filters and the ground electrodes between the plurality of magnetic sheets for the filters. Are connected in series.
[0097]
Reference numeral 31 denotes a noise filter according to the present embodiment. The noise filter 31 is generally constituted by an inductor unit 32 and a filter unit 46 described later.
[0098]
Numeral 32 denotes an inductor part which forms a damping resistor. The inductor part 32 includes, for example, four magnetic sheets 33 to 36 for inductors and inductors described later provided on the surfaces of the magnetic sheets 33 to 36 for inductors, respectively. It is constituted by transmission lines 37 to 40. The inductor magnetic sheets 33 to 36 are formed in a substantially rectangular plate shape, and are made of, for example, a ceramic material having magnetic characteristics such as ferrite.
[0099]
Reference numerals 37 to 40 denote transmission lines for inductors of a total of four layers disposed on the surfaces of the magnetic sheets 33 to 36, respectively. Each of the transmission lines 37 to 40 has a substantially U-shape having a folded portion made of a conductive metal material. Or it is formed in an arc shape.
[0100]
Here, one end of the transmission line 37 extends toward one end of the magnetic sheet for inductor 33 and forms an electrode portion 37A connected to a signal external electrode 59 described later. On the other hand, the other end side of the transmission line 37 is connected to one end side of the transmission line 38 through a through hole 41 which penetrates the magnetic sheet 33 and is filled with a conductive paste or the like. The other end of the transmission line 38 is connected to one end of the transmission line 39 through a through hole 42 penetrating the magnetic sheet 34, and the other end of the transmission line 39 is connected to a through hole 43 penetrating the magnetic sheet 35. It is connected to one end of the transmission line 40. Further, the other end of the transmission line 40 is connected to one end of a filter transmission line 51 to be described later through a through hole 44 penetrating the magnetic sheets 36 and 47.
[0101]
Thereby, the transmission lines 37 to 40 are connected in series with each other, and have a frame-shaped coil shape (spiral shape) having a substantially square or circular opening in the thickness direction of the magnetic sheets 33 to 36.
[0102]
The impedance value of the transmission lines 37 to 40 for the inductor is, for example, approximately equal to the difference between the characteristic impedance value of the transmission line to be connected to the noise filter 1 and the output impedance value of the driver IC at the clock frequency of the high-frequency signal. Is set to the value of Further, on the surface of the magnetic sheet for inductor 33, a magnetic sheet 45 is provided as a protective film for covering the transmission line 37 for inductor.
[0103]
Numeral 46 denotes a filter part which forms a distributed constant type filter. The filter part 46 is composed of four magnetic sheets 47-50 for filters provided on the rear surface of the magnetic sheet 36 for inductors stacked on the rear surface thereof. And transmission lines 51 and 52 for filters, which are provided between the magnetic sheets 47 and 48 and between the magnetic sheets 49 and 50 and connected in series with each other, and the surface of the magnetic sheet 47 and the magnetic sheets 48 and 49. And three ground electrodes 53 to 55 described later provided on the back surface of the magnetic material sheet 50, respectively.
[0104]
Thus, the transmission lines 51 and 52 and the ground electrode 54 are alternately stacked between the magnetic sheets 47 to 50 in a state where the ground electrodes 53 and 55 are arranged on the outermost layer and the outermost layer. On the back side of the magnetic material sheet 50, a magnetic material sheet 56 as a protective film covering the ground electrode 55 is provided.
[0105]
The magnetic sheets for filters 47 to 50 are sandwiched between the ground electrodes 53 to 55, and have a substantially rectangular plate shape substantially the same shape as the magnetic sheets for inductors 33 to 36, according to the first embodiment. The magnetic sheets 9 and 10 are formed of a ceramic material having magnetic properties, such as ferrite, substantially similar to the magnetic sheets 9 and 10.
[0106]
The magnetic sheets for a filter 47 to 50 are baked after being pressed in a state where they are superimposed on and stacked on the magnetic sheets 33 to 36, 45, and 56. Thus, the magnetic sheets 33 to 36, 45, 47 to 50, and 56 form a laminate 57.
[0107]
Reference numerals 51 and 52 denote transmission lines for filters provided between the magnetic sheets 47 and 48 for filters and between the magnetic sheets 49 and 50 for filters, respectively. The transmission line 51 for filters is the same as that of the first embodiment. In substantially the same manner as the transmission line 11, it is formed in a zigzag meandering substantially band shape using a conductive metal material such as silver paste or palladium, and has a constant width over its entire length.
[0108]
One end of the filter transmission line 51 is connected to the inductor transmission line 40 through the through hole 44 penetrating the magnetic sheets 36 and 47, and the other end of the filter transmission line 51 is connected to the magnetic sheet 48, The filter transmission line 52 is connected to one end of the filter transmission line 52 through a through hole 58 that penetrates the transmission line 49. The other end of the filter transmission line 52 extends toward the other end in the longitudinal direction of the magnetic sheet 50 and forms an electrode portion 52A connected to a signal external electrode 60 described later.
[0109]
The characteristic impedances of the transmission lines 51 and 52 are the same as the transmission line 11 according to the first embodiment, such as the width of the transmission lines 51 and 52, the distance between the adjacent ground electrodes 53 to 55, and the magnetic sheet 47. It is determined by the magnetic permeability and dielectric constant of ５０50. Therefore, by setting the width dimensions of the transmission lines 51 and 52 to substantially equal values and setting the thickness dimensions of the magnetic sheets 47 to 50 to substantially equal values, the entire lengths of the transmission lines 51 and 52 are set. The characteristic impedance can be set to a constant value.
[0110]
Reference numerals 53 to 55 denote a total of three ground electrodes provided between the magnetic sheets 47 to 50 so as to sandwich the transmission lines 51 and 52 of each layer. The ground electrode 53 is disposed on the surface of the magnetic sheet 47. The ground electrode 54 is disposed between the magnetic sheets 48 and 49, and the ground electrode 55 is disposed on the back surface of the magnetic sheet 50.
[0111]
The ground electrodes 53 to 55 are formed in a substantially rectangular flat plate shape using a conductive metal material, and cover the magnetic sheets 47 to 50 over substantially the entire surface. Further, the ground electrodes 53 to 55 are provided with electrode portions 53A to 55A protruding toward both ends in the width direction substantially in the same manner as the ground electrodes 12 and 13 according to the first embodiment. It is connected to a ground external electrode 61 described later.
[0112]
Reference numerals 59 and 60 denote first and second signal external electrodes made of a conductive metal material provided on both ends in the length direction of the laminate 57 (magnetic sheets 33 to 36, 45, 47 to 50, 56). Each of the signal external electrodes 59 and 60 covers the end face of the laminated body 57 in the same manner as the signal external electrodes 16 and 17 according to the first embodiment, and the front surface, the rear surface, and the side surface are also cylindrical. Covering. The signal external electrode 59 is connected to the electrode portion 37A of the inductor transmission line 37, and the signal external electrode 60 is connected to the electrode portion 52A of the filter transmission line 52.
[0113]
Reference numeral 61 denotes a ground external electrode made of a conductive metal material provided at each of both ends in the width direction at a middle position in the length direction of the laminate 57. The ground external electrode 61 has a substantially U-shape. The side surface of the body 57 extends in a band shape along the thickness direction, and a part thereof extends to the front surface and the back surface of the laminate 57. The ground external electrode 61 is connected to the electrode portions 53A to 55A of the ground electrodes 53 to 55.
[0114]
Thus, in the present embodiment configured as described above, substantially the same operation and effect as those in the first embodiment can be obtained. However, in the present embodiment, in particular, in the present embodiment, the inductor section 32 is formed of a multi-layer transmission line. 37 to 40 are connected in series, and the filter unit 46 is formed by connecting a plurality of transmission lines 51 and 52 in series. Therefore, the impedance of the inductor section 32 and the filter section 46 can be increased, and the heat loss with respect to the noise passing through the filter section 46 can be increased, and the attenuation can be increased.
[0115]
By setting the width dimensions of the transmission lines 51 and 52 and the thickness dimensions of the magnetic sheets 47 to 50 to substantially the same value, the characteristic impedance of the transmission lines 51 and 52 of the respective stacked layers becomes substantially equal to each other. Since they can be matched, the characteristic impedance does not change in the middle of the transmission lines 51 and 52, and impedance matching with an external circuit can be easily achieved.
[0116]
19 shows a noise filter according to a third embodiment of the present invention. The feature of the noise filter according to the present embodiment is that a magnetic sheet for a filter is provided on the back surface of a magnetic sheet for an inductor. The filter section is configured by providing a transmission line for a filter on the back surface of the magnetic sheet for use and a ground electrode between the magnetic sheet for the inductor and the magnetic sheet for filter. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
[0117]
Reference numeral 71 denotes a filter unit according to the present embodiment. The filter unit 71 includes one filter magnetic sheet 72 provided on the back surface of the inductor magnetic sheet 3 and a back surface of the magnetic sheet 72. And a later-described filter transmission line 73 connected in series to the inductor transmission line 4 and a later-described ground electrode 74 provided between the magnetic sheets 3 and 72 and provided on the surface of the magnetic sheet 72. It is constituted by. A magnetic sheet 75 as a protective film that covers the ground electrode 74 is provided on the back side of the magnetic sheet 72.
[0118]
The magnetic sheet for filter 72 is formed in a substantially rectangular plate shape having substantially the same shape as the magnetic sheet for inductor 3, and is formed of a ceramic material having magnetic characteristics such as ferrite. Then, the magnetic sheet for filter 72 is fired after being pressed in a state where the magnetic sheet for filter 72 overlaps with the magnetic sheets 3, 7, and 75 and is stacked. As a result, the magnetic sheets 3, 7, 72, and 75 form a laminate 76.
[0119]
Reference numeral 73 denotes a filter transmission line disposed on the back surface of the filter magnetic sheet 72. The filter transmission line 73 is formed in a zigzag shape by using a conductive metal material in substantially the same manner as the transmission line 11 according to the first embodiment. It has a constant width over its entire length. One end of the filter transmission line 73 is connected to the inductor transmission line 4 through the through hole 5 penetrating the magnetic sheets 3 and 72. On the other hand, the other end of the transmission line 73 for the filter extends toward the other end in the longitudinal direction of the magnetic sheet 72 and is connected to an electrode portion 73A connected to a second external electrode for signal (not shown). No.
[0120]
Reference numeral 74 denotes a ground electrode provided between the magnetic sheets 3 and 72 and provided on the surface of the magnetic sheet 72. The ground electrode 74 is electrically conductive similarly to the ground electrode 12 according to the first embodiment. It is formed in a substantially rectangular flat plate shape using a metal material, and covers the magnetic sheet 72 over substantially the entire surface. The ground electrode 74 is provided with an electrode portion 74A, and the electrode portion 74A is connected to a ground external electrode (not shown).
[0121]
Thus, in the present embodiment, since the transmission line 73 is provided on the back surface of the magnetic material sheet 72 and the transmission line 73 is covered by the ground electrode 74 provided on the surface of the magnetic material sheet 72, the filter unit 71 is configured. Similarly to the first embodiment, noise can be suppressed by utilizing the heat loss of the magnetic sheet 72 and the like.
[0122]
In addition, by appropriately setting the width dimension of the transmission line 73 and the thickness dimension of the magnetic sheet 72, the characteristic impedance of the noise filter can be set, and the characteristic impedance can be set to a substantially constant value regardless of the signal frequency. Can be held. For this reason, impedance matching can be achieved for circuits connected to the noise filter in almost all frequency ranges, and the reflection loss of the noise filter can be reduced.
[0123]
Further, since the transmission line 73 is covered over the entire length by the ground electrode 74, the characteristic impedance can be set to a constant value over the entire length of the transmission line 73, and noise can be prevented from being reflected in the middle of the transmission line 73. Can be suppressed.
[0124]
In particular, in the present embodiment, since the filter unit 71 is configured by using one ground electrode 74, the configuration of the filter unit 71 can be simplified as compared with the case of using two ground electrodes, and Cost can be reduced.
[0125]
In the first and third embodiments, the inductor section 2 including one magnetic sheet 3 and one layer of transmission line 4 is connected to the filter sections 8 and 71. However, the present invention is not limited to this. For example, as in the second embodiment, the inductor unit 32 including a plurality of magnetic sheets 33 to 36 and a plurality of transmission lines 37 to 40 may be replaced by the first and third inductors. It may be configured to be connected to the filter units 8 and 71 according to the embodiment.
[0126]
In the first embodiment, the magnetic sheets 9 and 10 are sandwiched between the two ground electrodes 12 and 13 with the transmission line 11 sandwiched between the two magnetic sheets 9 and 10. Thus, the filter unit 8 is formed, and the filter unit 8 is connected to the inductor unit 2. However, the present invention is not limited to this. For example, a filter in which transmission lines 51 and 52 and ground electrodes 53 to 55 are alternately arranged between a plurality of magnetic sheets 47 to 50 as in the second embodiment. The configuration may be such that the section 46 is connected to the inductor section 2 according to the first embodiment.
[0127]
In the above embodiments, the filter transmission lines 11, 51, 52, and 73 are formed in a meandering zigzag shape. However, the filter transmission lines may be formed in a linear or spiral shape. It is good also as a structure formed in a coil shape (spiral shape) over a plurality of layers like the inductor part 32 of the form.
[0128]
Further, as in the first modification shown in FIG. 20, the thickness T1 of the ground electrodes 12 'and 13' of the filter section 8 'may be formed smaller than the thickness T2 of the transmission line 11'. Thus, the thickness dimension of the entire noise filter can be reduced, and the size can be reduced. Further, since the thickness T2 of the transmission line 11 'can be made larger than the thickness T1 of the ground electrodes 12' and 13 ', the DC resistance of the transmission line 11' can be reduced, and the transmission line 11 'can be made larger. A current can flow.
[0129]
Further, in each of the above embodiments, the single noise filters 1 and 31 are provided with the single inductor sections 2 and 32 and the filter sections 8, 46 and 71. For example, the second modification shown in FIG. As in the example, a single noise filter 31 'may be provided with a plurality of inductor portions 32' and a plurality of filter portions 46 '.
[0130]
Further, in each of the above embodiments, the magnetic sheets 3, 9, 10, 33 to 36, 47 to 50, and 72 are formed of a ceramic material such as ferrite, and are fired. However, the present invention is not limited to this, and the magnetic sheet may be formed by mixing magnetic powder such as carbonyl iron in a resin material. This makes it possible to form a noise filter by joining the magnetic material sheets using an adhesive, so that manufacturing steps such as firing can be omitted, and productivity can be improved. In this case, the cutoff frequency of the noise filter is determined by the composition of the magnetic powder to be mixed, the ratio of the resin material to the magnetic powder, and the length of the transmission line.
[0131]
【The invention's effect】
As described above in detail, according to the first aspect of the present invention, since the inductor portion forming the damping resistor and the filter portion connected to the inductor portion for removing noise are integrally formed, the damping resistor is separately provided. As compared with the case, the assembling work can be simplified and the manufacturing cost can be reduced.
[0132]
In addition, since the filter section has a configuration in which a filter transmission line is provided between two filter magnetic sheets and these magnetic sheets are sandwiched between two ground electrodes, the heat loss of the filter magnetic sheet is reduced. Can suppress noise. Also, since the characteristic impedance of the transmission line for the filter can be maintained at a substantially constant value regardless of the frequency of the signal, impedance matching with an external circuit can be easily achieved, and the reflection loss of the noise filter is reduced. , Noise amplification can be prevented.
[0133]
Further, since the filter section has a configuration in which two magnetic sheets for a filter are sandwiched between two ground electrodes, a signal passing through the transmission line for the filter can be confined between the two ground electrodes, and a pass band can be obtained. Signal can be prevented from attenuating, and noise can be prevented from being mixed into an external transmission line, so that the signal can be transmitted reliably.
[0134]
According to the second aspect of the present invention, since the inductor section is constituted by the plurality of inductor magnetic sheets and the plurality of layers of the transmission lines for the inductor, in addition to the effect of the first aspect of the invention, the transmission section of the inductor is provided. The total length can be increased, and the impedance of the inductor section can be increased.
[0135]
According to the third aspect of the present invention, the filter section is configured by alternately arranging the filter transmission line and the ground electrode between the plurality of filter magnetic sheets, so that the total length of the filter transmission line is increased. Thus, the attenuation of noise passing through the filter transmission line can be increased.
[0136]
In this case, the inductor unit connected to the filter unit may be constituted by a plurality of inductor magnetic sheets and a plurality of inductor transmission lines.
[0137]
According to the fifth aspect of the present invention, the filter section is configured by providing the filter transmission line and the ground electrode with one filter magnetic sheet interposed therebetween. In addition, the configuration of the filter unit can be simplified, and the manufacturing cost can be reduced.
[0138]
In this case, the inductor unit connected to the filter unit may be constituted by a plurality of inductor magnetic sheets and a plurality of inductor transmission lines.
[0139]
According to the seventh aspect of the present invention, the impedance value of the transmission line for the inductor is set to a value substantially equal to the difference between the characteristic impedance value of the transmission line to be connected and the output impedance value of the driver IC at the signal frequency. Therefore, impedance matching can be achieved between the transmission line to be connected and the transmission line for the inductor, and the reflection of the high-frequency signal to be transmitted can be reduced and transmitted reliably.
[0140]
According to the eighth aspect of the present invention, since the filter transmission line is formed in a zigzag shape meandering, the length dimension can be increased as compared with the case where the filter transmission line is formed linearly, and noise can be reduced. Can be increased.
[0141]
According to the ninth aspect of the present invention, since the transmission line for the filter is formed in a spiral shape, the magnetic flux formed by the transmission line for the filter can be added to each other, the inductance can be increased, and the filter unit can be increased. Can be increased.
[0142]
According to the tenth aspect of the present invention, the magnetic sheet for the inductor and the magnetic sheet for the filter are formed in a substantially quadrangular shape. The first and second signal external electrodes are connected to each other, and a ground external electrode connected to the ground electrode is provided at a middle position in the length direction of these magnetic sheets. Signal external electrodes located at both ends in the length direction of the magnetic sheet can be easily connected to the middle of the extending wiring. In addition, the ground external electrode provided at the intermediate position in the length direction of the magnetic sheet can be easily connected to the ground terminal provided around the wiring, so that the noise filter can be easily assembled. it can.
[0143]
According to the eleventh aspect of the present invention, the relative magnetic permeability μ of the magnetic sheet for a filter. _r Is 4 ≦ μ _r ≦ 30 and L / √ (μ _r -1) Since the length L of the filter transmission line is set so as to satisfy ≧ 3, the cutoff frequency range can be easily set within the practical frequency band of 200 MHz ≦ fc ≦ 2 GHz. it can. Also, the relative permeability μ of the magnetic sheet for the filter _r Is 4 ≦ μ _r ≦ 30, L / √ (μ _r -1) ≧ 3, the slope of the noise attenuation curve is set to, for example, 20 dB / dec. As described above, the difference between the signal and noise attenuation can be increased.
[0144]
According to the twelfth aspect of the invention, since the thickness of the ground electrode is formed smaller than the thickness of the transmission line for the filter, the thickness of the entire noise filter can be reduced, and the size can be reduced. Can be. Further, since the thickness of the filter transmission line can be made thicker than the ground electrode, the DC resistance of the transmission line can be reduced, and a larger current can flow.
[0145]
According to the thirteenth aspect of the present invention, since the magnetic material sheet is formed of a ceramic material having magnetic properties, a noise filter can be formed by firing the magnetic material sheets in an overlapping state. In this case, it is preferable that the magnetic material sheet is formed of sintered ferrite.
[0146]
According to the invention of claim 15, since the magnetic material sheet is formed of a resin material mixed with magnetic powder, a noise filter can be formed by joining the magnetic material sheets using an adhesive, and firing and the like can be performed. Can be omitted, and the productivity can be improved.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a noise filter according to a first embodiment.
FIG. 2 is an exploded perspective view showing the noise filter in FIG. 1 in an exploded manner.
FIG. 3 is a cross-sectional view of the noise filter as viewed from a direction indicated by arrows III-III in FIG.
FIG. 4 is a cross-sectional view of the noise filter as viewed from a direction indicated by arrows IV-IV in FIG. 1;
FIG. 5 is a plan view of a transmission line for a filter and the like as viewed from a direction indicated by arrows VV in FIG. 2;
FIG. 6 is an enlarged cross-sectional view showing a main part of FIG.
FIG. 7 is a circuit diagram showing a state in which the noise filter in FIG. 1 is connected to a transmission line or the like.
FIG. 8 is an equivalent circuit diagram showing the noise filter in FIG.
FIG. 9 shows a relative magnetic permeability μ of a magnetic sheet. _r FIG. 9 is a characteristic diagram showing a relationship between the frequency of a signal and the amount of attenuation when is set to 10.
FIG. 10 is a characteristic diagram showing the relationship between signal frequency and attenuation when the length L of the filter transmission line is set to 50 mm.
FIG. 11 is a characteristic diagram illustrating a relationship between a signal frequency and an attenuation when a constant C is set to 20 mm.
FIG. 12 is a characteristic diagram showing a relationship between a signal frequency and an attenuation when a constant C is set to 3 mm.
FIG. 13 is a characteristic diagram showing a relationship between a constant C and a slope of an attenuation curve.
FIG. 14 shows a cutoff frequency fc and a relative magnetic permeability μ of a magnetic sheet for a filter. _r FIG. 4 is a characteristic diagram showing the relationship between
FIG. 15 is a perspective view showing a noise filter according to a second embodiment.
FIG. 16 is an exploded perspective view showing the noise filter in FIG. 15 in an exploded manner.
17 is a cross-sectional view of the noise filter as viewed from the direction indicated by arrows XVII-XVII in FIG.
FIG. 18 is a cross-sectional view of the noise filter as viewed in a direction indicated by arrows XVIII-XVIII in FIG.
FIG. 19 is an exploded perspective view showing an exploded noise filter according to the third embodiment.
FIG. 20 is an enlarged cross-sectional view of a main part at the same position in FIG. 6 showing an enlarged filter portion of the noise filter according to the first modified example.
FIG. 21 is an exploded perspective view showing a noise filter according to a second modification in an exploded manner.
[Explanation of symbols]
1,31,31 'noise filter
2,32,32 'inductor part
3,33-36,33'-36 'Magnetic sheet for inductor
4,37-40,37'-40 'Transmission line for inductor
8, 46, 71, 8 ', 46' filter section
9,10,47-50,72,47'-50 'Magnetic sheet for filter
11,51,52,73,11 ', 51', 52 'Transmission line for filter
12, 13, 53 to 55, 74, 12 ', 13', 53 'to 55' Ground electrode
16, 17, 59, 60 External electrode for signal
18,61 External electrode for ground

Claims (15)

A noise filter comprising an inductor part forming a damping resistor and a filter part connected to the inductor part and removing noise,
The inductor portion is configured by a magnetic sheet for inductor and a transmission line for inductor provided on a surface of the magnetic sheet for inductor.
The filter unit is provided on the back surface of the inductor magnetic sheet and is provided with two filter magnetic sheets overlapping each other, and is disposed between the two magnetic sheets and connected in series to the inductor transmission line. Filter comprising: a transmission line for a filter; and two ground electrodes provided on each of the magnetic sheets for the filter, and including the transmission lines for the filter and sandwiching the two magnetic sheets for the filter. . A noise filter comprising an inductor part forming a damping resistor and a filter part connected to the inductor part and removing noise,
The inductor unit includes a plurality of inductor magnetic sheets overlapping each other, and an inductor transmission line provided on the surface of each inductor magnetic sheet and connected in series with each other,
The filter section includes two magnetic sheets for a filter, which are stacked on the magnetic sheet for an inductor on the rearmost side of the plurality of magnetic sheets for an inductor and overlap each other, and a space between the two magnetic sheets. And a filter transmission line connected in series to the inductor transmission line, and two filter magnetic sheets provided on each of the filter magnetic sheets and including the filter transmission lines. A noise filter composed of a single ground electrode. A noise filter comprising an inductor part forming a damping resistor and a filter part connected to the inductor part and removing noise,
The inductor portion is configured by a magnetic sheet for inductor and a transmission line for inductor provided on a surface of the magnetic sheet for inductor.
The filter section is provided with a plurality of filter magnetic sheets stacked on the back surface of the inductor magnetic sheet and overlapping each other, and ground electrodes on the outermost surface layer and the lowermost layer of each of the filter magnetic sheets. In the arrangement state, the filter transmission lines and the ground electrodes are alternately stacked between the respective filter magnetic sheets, and a plurality of layers of the filter transmission lines are connected in series, and one end thereof is connected to the inductor transmission line. A noise filter configured to be connected in series. A noise filter comprising an inductor part forming a damping resistor and a filter part connected to the inductor part and removing noise,
The inductor unit includes a plurality of inductor magnetic sheets overlapping each other, and an inductor transmission line provided on the surface of each inductor magnetic sheet and connected in series with each other,
The filter unit is provided with a plurality of magnetic sheets for filters that are provided to be stacked on the magnetic sheet for inductor on the rearmost surface side of the plurality of magnetic sheets for inductor and overlap with each other. With the ground electrodes arranged on the outermost layer and the lowermost layer, the transmission lines for filters and the ground electrodes are alternately stacked between the magnetic sheets for each filter, and a plurality of transmission lines for filters are connected in series. A noise filter having one end connected in series to the transmission line for the inductor. A noise filter comprising an inductor part forming a damping resistor and a filter part connected to the inductor part and removing noise,
The inductor portion is configured by a magnetic sheet for inductor and a transmission line for inductor provided on a surface of the magnetic sheet for inductor.
The filter section includes a filter magnetic sheet stacked on the back surface of the inductor magnetic sheet and a filter transmission line provided on the back surface of the filter magnetic sheet and connected in series to the inductor transmission line. A noise filter comprising: a line; and a ground electrode provided between the magnetic sheet for the filter and the magnetic sheet for the inductor, and covering the transmission line for the filter over the entire length. A noise filter comprising an inductor part forming a damping resistor and a filter part connected to the inductor part and removing noise,
The inductor unit includes a plurality of inductor magnetic sheets overlapping each other, and an inductor transmission line provided on the surface of each inductor magnetic sheet and connected in series with each other,
The filter section is a magnetic sheet for a filter provided by being stacked on the magnetic sheet for the inductor on the rearmost side of the plurality of magnetic sheets for an inductor, and the filter section is provided on the back surface of the magnetic sheet for the filter. A filter transmission line connected in series to the inductor transmission line, and a ground electrode provided between the filter magnetic sheet and the inductor magnetic sheet and covering the entire length of the filter transmission line. Noise filter. The impedance value of the transmission line for the inductor is set to a value substantially equal to a difference between a characteristic impedance value of a transmission line to be connected and an output impedance value of a driver IC at a signal frequency. The noise filter according to 2, 3, 4, 5, or 6. The noise filter according to claim 1, 2, 3, 4, 5, 6, or 7, wherein the filter transmission line is formed in a meandering zigzag shape. The noise filter according to claim 1, 2, 3, 4, 5, 6, or 7, wherein the filter transmission line is formed in a spiral shape. The magnetic sheet for the inductor and the magnetic sheet for the filter are formed in a rectangular shape, and a first signal external electrode connected to the transmission line for the inductor is provided on one end side in the length direction of the magnetic sheet. A second signal external electrode connected to the filter transmission line is provided on the other end of the magnetic sheet in the longitudinal direction, and a ground connected to the ground electrode is provided at an intermediate position in the longitudinal direction of the magnetic sheet. 10. The noise filter according to claim 1, further comprising an external electrode for use. When the cutoff frequency is in the range of 200 MHz to 2 GHz, the relative magnetic permeability of the filter magnetic sheet is μ _r , and the length of the filter transmission line is L [mm], 4 ≦ μ _r ≦ 30 The noise filter according to any one of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10, wherein L / √ (μ _r -1) ≧ 3 mm. The thickness of the ground electrode is smaller than the thickness of the transmission line for the filter, according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11. Noise filter. 13. The magnetic sheet for an inductor and the magnetic sheet for a filter are formed of a ceramic material having magnetic properties. The noise filter according to 1. 13. The magnetic sheet according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, wherein the magnetic sheet for inductor and the magnetic sheet for filter are formed of sintered ferrite. Noise filter. 13. The magnetic sheet for an inductor and the magnetic sheet for a filter are formed of a resin material mixed with a magnetic powder. The noise filter according to 1.

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