JP4477163B2

JP4477163B2 - Feedforward distortion compensation circuit

Info

Publication number: JP4477163B2
Application number: JP18416999A
Authority: JP
Inventors: 正人曾根; 健一河野; 良次伊藤
Original assignee: Japan Radio Co Ltd
Current assignee: Japan Radio Co Ltd
Priority date: 1999-06-29
Filing date: 1999-06-29
Publication date: 2010-06-09
Anticipated expiration: 2019-06-29
Also published as: JP2001016046A

Description

【０００１】
【発明の属する技術分野】
本発明は、主増幅器にて発生する歪成分を除去乃至抑圧するために使用されるフィードフォワード歪補償回路に関する。
【０００２】
【従来の技術】
増幅器は一般に非線形性を有しているため、比較的広い周波数帯域に亘り分布する信号群を増幅するとその非線形性に起因する各種の歪が発生する。例えば、日本にて実施予定の地上波ディジタルテレビジョン放送システムでは、直交関係が成り立つよう多数のキャリアを周波数軸上に配置・多重化するＯＦＤＭ(Orthogonal Frequency Division Multiplex)方式を用いている。ＯＦＤＭ方式に従い多重化された信号を増幅する場合、キャリア成分同士の相互変調による歪即ち相互変調歪が発生する。特に、そのキャリア間隔が狭い場合、フィルタ等の手段では、増幅出力中のキャリア成分と相互変調歪成分とを分離するのが難しい。なお、増幅器の非線形性の問題は、ＣＤＭＡ(Code Division Multiple Access)方式を用いる携帯電話システム特にその基地局・中継局における電力増幅の際にも発生する。
【０００３】
こういった歪成分を除去乃至抑圧するための回路上の工夫としては、プリディストーション方式、フィードフォワード方式等がある。これらのうちフィードフォワード方式は、主増幅器への入力信号の一部を主増幅器の出力側にフィードフォワードして歪成分を取り出し、取り出した歪成分を更にフィードフォワードして出力中の歪成分を打ち消し除去乃至抑圧する、という原理に基づいている。
【０００４】
図１に、フィードフォワード方式による歪補償回路を備える歪補償増幅器の構成を示す。この図の回路に入力される信号は、主増幅器Ａ１や遅延回路ＤＬ２を経て図示しないアンテナ等に出力される。この入出力経路は、主増幅器Ａ１により増幅されるべき信号及び増幅された信号が通る経路であるため、本線と呼ぶことができる。主増幅器Ａ１に前置されている方向性結合器ＤＣ１は、入力信号を増幅のため主増幅器Ａ１に供給する一方で、主増幅器Ａ１に供給する信号と周波数構成上は同一であるが振幅が小さい信号を分岐し、遅延回路ＤＬ１経由で方向性結合器ＤＣ２へ供給している。方向性結合器ＤＣ２は、主増幅器Ａ１の出力信号を遅延回路ＤＬ２経由で方向性結合器ＤＣ３に供給する一方で、主増幅器Ａ１の出力信号と周波数構成上は同一であるが振幅が小さい信号を分岐し、これを更に遅延回路ＤＬ１経由で供給される信号と結合させ、それによって生成した抽出歪信号を歪増幅器Ａ２に供給している。方向性結合器ＤＣ３は、遅延回路ＤＬ２経由で供給される信号と、歪増幅器Ａ２からの入力とを所定利得で以て結合させることにより、歪補償出力信号を生成してアンテナ等に出力する。
【０００５】
ここに、同軸遅延線等により構成される遅延回路ＤＬ１の遅延時間は、方向性結合器ＤＣ１から主増幅器Ａ１を経て方向性結合器ＤＣ２に至る本線上の経路で発生する遅延時間と、一致させておくものとする。また、この本線上の経路又は遅延回路ＤＬ１の前又は後に、信号の振幅及び位相又はＩ，Ｑ各成分値を調整するための変調器Ｍ１を設ける。この変調器Ｍ１は、方向性結合器ＤＣ２にて相互に結合される２種類の信号中のキャリア成分が相互に同振幅・逆位相になるよう、設定乃至制御されているものとする。その場合、方向性結合器ＤＣ２から歪増幅器Ａ２側に出力される抽出歪信号は、概ね、主増幅器Ａ１にてその非線形性が原因で生じた歪成分のみを、含む信号となる。そのため、方向性結合器ＤＣ１から方向性結合器ＤＣ２に至るループ、即ち分岐した入力信号を遅延回路ＤＬ１にて遅延させ方向性結合器ＤＣ２に供給して抽出歪信号を発生させるフィードフォワードループは、歪抽出ループと呼ぶことができる。
【０００６】
また、同軸遅延線等により構成される遅延回路ＤＬ２の遅延時間は、方向性結合器ＤＣ２から歪増幅器Ａ２を経て方向性結合器ＤＣ３に至る経路で発生する遅延時間と、一致させておくものとする。また、この経路又は遅延回路ＤＬ２の前又は後に、信号の振幅及び位相又はＩ，Ｑ各成分値を調整する変調器Ｍ２を設ける。この変調器Ｍ２は、方向性結合器ＤＣ３にて相互に結合される２種類の信号中の歪成分が相互に同振幅・逆位相になるよう、設定乃至制御されているものとする。その場合、方向性結合器ＤＣ３から歪補償出力信号として出力される信号は、概ね、上述した歪成分が除去乃至抑圧された信号となる。そのため、方向性結合器ＤＣ２から方向性結合器ＤＣ３に至るループ、即ち抽出歪信号を歪増幅器Ａ２により増幅して方向性結合器ＤＣ３に供給し歪補償出力信号を発生させるフィードフォワードループは、歪除去ループと呼ぶことができる。
【０００７】
制御部ＣＴＬは、抽出歪信号中にキャリア成分が漏れ出さないよう歪抽出ループの動作特に変調器Ｍ１における調整動作を制御し、また、歪補償出力信号中に歪成分特に相互変調歪成分が漏れ出さないよう歪除去ループの動作特に変調器Ｍ２における調整動作を制御する。制御部ＣＴＬによる制御は、例えば、パイロット信号の挿入及びその検出という手法を用いて行う。或いは、本願出願人が先に提案しているように同期検波技術を用いて行う等、他の手法を用いて行う。加えて、方向性結合器ＤＣ１〜ＤＣ３は、例えば図示の如くハイブリッド回路により実現する。変調器Ｍ１及びＭ２は、直交変調器とするか、或いは、可変利得増幅器若しくは可変減衰器と可変移相器の組合せとする。
【０００８】
【発明が解決しようとする課題】
しかしながら、実際には、使用する周波数帯域全域に亘り抽出歪信号へのキャリア成分の漏れ出しを防ぐことには、困難さがある。
【０００９】
まず、図１に示した回路では、方向性結合器ＤＣ２において抽出歪信号中にキャリア成分が漏れ出さないように、制御部ＣＴＬの制御の下に変調器Ｍ１により振幅・位相等の調整を実行する。例えば、１ＧＨｚで４０ｄＢのキャリア抑圧量（即ち主増幅器Ａ１の出力に対する抽出歪信号中のキャリア成分の比）が得られるよう、遅延回路ＤＬ１の遅延時間を設定しかつ変調器Ｍ１を制御する。このとき、遅延回路ＤＬ１における遅延時間に誤差τが生じていると、この遅延時間設定誤差τは位相制御誤差２πｆτとなって現れる。即ち、ある特定の周波数にてキャリア成分を理想的に打消・抑圧することができていても、その周波数から離れるにつれ位相制御誤差２πｆτが増大し抑圧量は減っていく。
【００１０】
従って、仮に、１ＧＨｚで４０ｄＢのキャリア抑圧量が得られるよう遅延回路ＤＬ１における遅延時間を設定したとしても、遅延回路ＤＬ１における遅延時間に例えば６０ｐｓｅｃの設定誤差τが生じていれば、そこから６０ＭＨｚ離れている１．０６ＧＨｚにおいては例えば約３６ｄＢしかキャリア抑圧量が得られない。即ち、無視し得ない量のキャリア成分が抽出歪信号中に漏れ出す。６０ｐｓｅｃの誤差τは同軸遅延線でいえば１８ｍｍというわずかな電気長であり、遅延回路ＤＬ１を同軸遅延線にて構成する場合往々にして発生する。
【００１１】
結果として、数十ＭＨｚ以上に広がる十分広い周波数帯域に亘り十分大きなキャリア抑圧量を得ようとするのであれば、遅延時間の設定誤差τを非常に小さくしなければならなくなる。更に、遅延回路ＤＬ１をはじめとして、歪抽出ループ内又はその周辺の部材には温度特性がある。この温度特性によっても、キャリア抑圧量の低下が発生する。
【００１２】
本発明は、このような問題点を解決することを課題としてなされたものであり、抽出歪信号に漏れ出すキャリア成分を従来より広い周波数帯域に亘り確実に抑圧できるようにすること、従来に比べ遅延時間をラフに設定することが許容されるようにすること、温度等のパラメータに対して歪抽出ループの動作を安定化すること、ノイズに強くまたより短時間で最適動作状態に引き込めるようにすること等を、その目的とする。
【００１３】
【課題を解決するための手段】
このような目的を達成するために、本発明は、（１）キャリア成分を含む入力信号を増幅し出力する主増幅器に付設され当該主増幅器の非線形性により当該主増幅器から出力される歪成分を除去乃至抑圧するために用いられる歪補償回路であって、（２）上記入力信号から分岐した信号をフィードフォワードし上記主増幅器の出力信号から分岐した信号と結合させることにより抽出歪信号を生成する歪抽出ループと、この抽出歪信号をフィードフォワードし上記出力信号に結合させることにより歪補償出力信号を生成する歪除去ループと、歪抽出ループ及び歪除去ループにおける信号調整動作を制御する制御部とを備え、抽出歪信号へのキャリア成分の漏れが抑圧されるようまた歪補償出力信号への歪成分の漏れが抑圧されるよう上記制御部が上記制御を実行するフィードフォワード歪補償回路において、（３）上記歪抽出ループは、上記入力信号を２分岐し、分岐した一方の信号を増幅のため上記主増幅器に供給する第１方向性結合器と、上記第１方向性結合器から分岐した他方の信号を２分岐する分配器と、上記分配器から分岐した一方の信号と上記主増幅器の出力信号とを結合し第１抽出歪信号を出力すると共に、当該第１抽出歪信号とは別に上記主増幅器の出力信号を出力する第２方向性結合器と、上記分配器から分岐した他方の信号と上記第１抽出歪信号とを結合し第２抽出歪信号を出力する第３方向性結合器と、上記第３方向性結合器によって結合される２つの信号のうちいずれかの振幅および位相を上記制御部の制御に基づいて調整する第３方向性結合器用変調器と、を備え、上記歪除去ループは、上記第２方向性結合器から出力された上記主増幅器の出力信号と、上記第２抽出歪信号とを結合し上記歪補償出力信号を出力する第４方向性結合器、を備えることを特徴とする。
【００１４】
また、本発明に係るフィードフォワード歪補償回路においては、上記歪抽出ループは、上記第２方向性結合器によって結合される２つの信号のうちいずれかの振幅および位相を上記制御部の制御に基づいて調整する第２方向性結合器用変調器を備え、上記歪除去ループは、上記第４方向性結合器によって結合される２つの信号のうちいずれかの振幅および位相を上記制御部の制御に基づいて調整する第４方向性結合器用変調器を備えることが好適である。また、本発明に係るフィードフォワード歪補償回路においては、上記第２方向性結合器用変調器、上記第３方向性結合器用変調器、および上記第４方向性結合器用変調器は、処理対象の信号のＩ成分値およびＱ成分値を調整することで、当該処理対象の信号の振幅および位相を調整する直交変調器であることが好適である。
【００１５】
また、本発明は、キャリア成分を含む入力信号を増幅し出力する主増幅器に付設され当該主増幅器の非線形性により当該主増幅器から出力される歪成分を除去乃至抑圧するために用いられる歪補償回路であって、上記入力信号から分岐した信号をフィードフォワードし上記主増幅器の出力信号から分岐した信号と結合させることにより抽出歪信号を生成する歪抽出ループと、この抽出歪信号をフィードフォワードし上記出力信号に結合させることにより歪補償出力信号を生成する歪除去ループと、歪抽出ループ及び歪除去ループにおける信号調整動作を制御する制御部とを備え、抽出歪信号へのキャリア成分の漏れが抑圧されるようまた歪補償出力信号への歪成分の漏れが抑圧されるよう上記制御部が上記制御を実行するフィードフォワード歪補償回路において、上記歪抽出ループは、上記入力信号を２分岐し、分岐した一方の信号を増幅のため上記主増幅器に供給する第１方向性結合器と、上記第１方向性結合器から分岐した他方の信号を初段で２分岐し、前段から分岐した一方の信号を次段で２分岐するよう縦続接続された複数の分配器と、上記初段の分配器から分岐し、次段へと至らない一方の信号と上記主増幅器の出力信号とを結合し第１抽出歪信号を出力すると共に、当該第１抽出歪信号とは別に上記主増幅器の出力信号を出力する第２方向性結合器と、上記初段の分配器よりも後段の分配器から分岐した、分岐末端の各信号に対応して設けられ、初段に上記第１抽出歪信号が入力され、初段に対応する分岐信号と上記第１抽出歪信号とが結合され、前段から出力された信号に次段に対応する分岐信号が結合されるよう縦続接続された縦続接続方向性結合器と、を備え、最終段の上記縦続接続方向性結合器から第２抽出歪信号を出力し、上記歪除去ループは、上記第２方向性結合器から出力された上記主増幅器の出力信号と、上記第２抽出歪信号とを結合し上記歪補償出力信号を出力する出力方向性結合器、を備えることを特徴とする。
【００１６】
また、本発明に係るフィードフォワード歪補償回路においては、上記第２方向性結合器、上記縦続接続方向性結合器、および上記出力方向性結合器に対応して設けられ、結合される２つの信号のうちいずれかの振幅および位相を上記制御部の制御に基づいて調整する変調器を備えることが好適である。また、本発明に係るフィードフォワード歪補償回路においては、各変調器は、処理対象の信号のＩ成分値およびＱ成分値を調整することで、当該処理対象の信号の振幅および位相を調整する直交変調器とすることが好適である。
【００１８】
従来技術において問題となっていた事項、即ち、十分なキャリア抑圧量を得ることができる周波数帯域の狭さ、という問題点は、歪抽出ループを構成する部材が有している位相周波数特性が原因で、発生していた。言い換えれば、歪抽出ループを単一のループにより構成していたため、そのループにおける一般に急峻な勾配の位相周波数特性がそのまま歪抽出ループ全体の位相周波数特性となっており、その結果、十分なキャリア抑圧量を得ることができる周波数帯域も狭くなっていた。これに対し、本発明においては、複数のループを多重化することで、各ループの位相周波数特性の勾配が従来と同様急峻であっても、歪抽出ループ全体ではその位相周波数特性の勾配が緩くなるようにし、それによって、十分なキャリア抑圧量を得ることができる周波数帯域を拡げている。
【００１９】
その結果、歪抽出ループを構成する回路例えば遅延回路の設計・設定を従来に比べラフに行っても構わなくなり、また、温度に対しても安定になる。更に、方向性結合器１段当たりのキャリア抑圧量が、従来技術の結合部材（方向性結合器ＤＣ２）におけるキャリア抑圧量より小さいため、従来技術に比べノイズの影響を受けにくくまた最適な調整状態への引込に要する時間も短くなる。
【００２０】
【発明の実施の形態】
以下、本発明の好適な実施形態に関し図面に基づき説明する。なお、図１に示した従来技術と同様の又は対応する構成には同一の符号を付し、重複する説明を省略する。
【００２１】
図２に、本発明の一実施形態に係る回路の構成を示す。この実施形態は、図１に示した従来技術に、分配器Ｄ１、遅延回路ＤＬ１Ａ、変調器Ｍ１Ａ、方向性結合器ＤＣ２Ａ及び安定化用増幅器Ａ３を付加した構成を有している。分配器Ｄ１は、方向性結合器ＤＣ１にて本線から分岐された信号を２分配し、その一方を遅延回路ＤＬ１経由で方向性結合器ＤＣ２へ、他方を遅延回路ＤＬ１Ａ及び変調器Ｍ１Ａ経由で方向性結合器ＤＣ２Ａへ、供給する。即ち、本実施形態では、方向性結合器ＤＣ１及び分配器Ｄ１が、前述のＮ分岐用の分岐部材に該当する。Ｎは３に設定されている。
【００２２】
また、方向性結合器ＤＣ２Ａは例えばハイブリッドであり、遅延回路ＤＬ１Ａ及び変調器Ｍ１Ａ経由で入力した信号と、方向性結合器ＤＣ２にて本線から分岐され遅延回路ＤＬ１経由の信号と結合され安定化用増幅器Ａ３経由で入力した信号とを、結合させる。方向性結合器ＤＣ２Ａは、その結果得られた信号を抽出歪信号として歪除去ループに供給する。即ち、本実施形態では、前述したＮ−１段の結合部材として方向性結合器ＤＣ２及びＤＣ２Ａを設けている。
【００２３】
遅延回路ＤＬ１における遅延時間は、方向性結合器ＤＣ１内の分岐点から変調器Ｍ１及び主増幅器Ａ１を経て方向性結合器ＤＣ２内の結合点に到る経路における信号遅延と、方向性結合器ＤＣ１内の分岐点から分配器Ｄ１及び遅延回路ＤＬ１を経て方向性結合器ＤＣ２内の結合点に到る経路における信号遅延とが等しくなるよう、設定されている。また、遅延回路ＤＬ１Ａにおける遅延時間は、方向性結合器ＤＣ１内の分岐点から変調器Ｍ１、主増幅器Ａ１、方向性結合器ＤＣ２及び安定化用増幅器Ａ３を経て方向性結合器ＤＣ２Ａ内の結合点に到る経路における信号遅延と、方向性結合器ＤＣ１内の分岐点から分配器Ｄ１、遅延回路ＤＬ１Ａ及び変調器Ｍ１Ａを経て方向性結合器ＤＣ２Ａ内の結合点に到る経路における信号遅延とが等しくなるよう、設定されている。
【００２４】
制御部ＣＴＬは、方向性結合器ＤＣ２にて結合される信号中のキャリア同士が同振幅・逆位相になるよう変調器Ｍ１を制御する。制御部ＣＴＬは、方向性結合器ＤＣ２Ａにて結合される信号中のキャリア同士が同振幅・逆位相になるよう変調器Ｍ１Ａを制御する。なお、変調器Ｍ１Ａは変調器Ｍ１と同じ回路構成でよい。また、制御部ＣＴＬによる変調器Ｍ１及びＭ１Ａの制御の方法については、従来技術における変調器Ｍ１の制御方法を転用する等、各種の方法を採用できる。
【００２５】
従来技術においては、遅延回路ＤＬ１における遅延時間を精密に設定しないと、増幅器を使用する周波数帯域にて十分なキャリア抑圧量を得ることができなかった。本実施形態の利点の一つは、遅延回路ＤＬ１及びＤＬ１Ａにおける遅延時間をさほど精密に設定しなくても、十分なキャリア抑圧量が得られる周波数帯域を拡げることができることにある。即ち、歪抽出ループを本実施形態の如く二重にすれば、歪抽出ループを構成する各ループの位相周波数特性が従来技術における歪抽出ループのそれと同程度の勾配を有しているにしても、歪抽出ループ全体での位相周波数特性の勾配は緩くなる。その結果、振幅・位相調整の下での結合によるキャリア抑圧が十分に働く周波数帯域、即ち歪抽出ループにおけるキャリア抑圧量が十分大きくなる周波数帯域が広がる。言い換えれば、従来に比べ遅延時間設定をラフにしても、従来と同程度以上の周波数帯域に亘りキャリアを好適に抑圧できる。
【００２６】
また、このように多重化された歪抽出ループを用いることにより、温度変化をはじめとする環境変化による遅延時間の変化等にも強くなる。また、歪抽出ループを構成するＮ−１個のループにおける振幅・位相調整量が、ループ１個当たりで見た場合少なくなるため、制御部ＣＴＬによるその制御がより安定になり最適動作状態への引込も迅速化する。特に、方向性結合器ＤＣ２から方向性結合器ＤＣ２Ａに供給される信号を増幅しそのレベルを高めることにより、ノイズに対して強くより安定な歪抽出ループを得ることができる。
【００２７】
なお、図２に示した回路は本発明の一実施形態に過ぎない。本発明は、図２に示した回路に各種の変形を施した回路として実施することもできる。例えば、図２中の安定化用増幅器Ａ３は、それなしでも十分な安定性を得られる場合には省略できる。また、図２ではＮ＝３であったが、図３に示すようにＮ＝４としてもよい。図３中、Ｄ２は分配器Ｄ１と同様の構成を有する分配器、ＤＬ１Ｂは遅延回路、Ｍ１Ｂは変調器、ＤＣ２Ｂは方向性結合器、Ａ４は安定化用増幅器であり、制御部ＣＴＬは変調器Ｍ１Ｂをも制御する。安定化用増幅器Ａ３と同様、安定化用増幅器Ａ４も省略できる。無論、Ｎ＞４とすることもできる。また、変調器Ｍ１を図４に示すように遅延回路ＤＬ１側に移動させてもよい。図５にＸ１〜Ｘ４の記号で示すように遅延回路ＤＬ１及びＤＬ１Ａを移動させてもよい。遅延回路ＤＬ１及びＤＬ１Ａは、その一部又は全部を、一つの遅延回路にまとめることができる。そして、歪抽出ループを構成するＮ−１個のループは、増幅器を使用する周波数帯域即ちキャリアが分布する周波数帯域内のいずれかの周波数で、そのループ単独でのキャリア抑圧量が最大になるよう、設計する。キャリア抑圧量最大の周波数をループ間で厳密に一致させる必要はない。
【図面の簡単な説明】
【図１】従来技術に係る回路の構成を示すブロック図である。
【図２】本発明の一実施形態に係る回路の構成を示すブロック図である。
【図３】この実施形態の変形例特にその歪抽出ループ部分を示すブロック図である。
【図４】この実施形態の他の変形例特にその変調器配置を示すブロック図である。
【図５】この実施形態の更に他の変形例特にその遅延回路配置を示すブロック図である。
【符号の説明】
Ａ１主増幅器、Ａ２歪増幅器、Ａ３，Ａ４安定化用増幅器、ＣＴＬ制御部、Ｄ１，Ｄ２分配器、ＤＣ１〜ＤＣ３，ＤＣ２Ａ，ＤＣ２Ｂ方向性結合器、ＤＬ１，ＤＬ１Ａ，ＤＬ１Ｂ，ＤＬ２遅延回路、Ｍ１，Ｍ１Ａ，Ｍ１Ｂ，Ｍ２変調器。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a feedforward distortion compensation circuit used for removing or suppressing a distortion component generated in a main amplifier.
[0002]
[Prior art]
Since an amplifier generally has nonlinearity, various distortions due to the nonlinearity are generated when a signal group distributed over a relatively wide frequency band is amplified. For example, a terrestrial digital television broadcasting system scheduled to be implemented in Japan uses an OFDM (Orthogonal Frequency Division Multiplex) system in which a large number of carriers are arranged and multiplexed on the frequency axis so that an orthogonal relationship is established. When a signal multiplexed according to the OFDM method is amplified, distortion due to intermodulation between carrier components, that is, intermodulation distortion occurs. In particular, when the carrier interval is narrow, it is difficult to separate the carrier component and the intermodulation distortion component in the amplified output by means such as a filter. The problem of the nonlinearity of the amplifier also occurs when power is amplified in a mobile phone system using a CDMA (Code Division Multiple Access) system, particularly in its base station / relay station.
[0003]
As a device on the circuit for removing or suppressing such distortion components, there are a predistortion method, a feedforward method, and the like. Of these, the feed-forward method feeds a part of the input signal to the main amplifier to the output side of the main amplifier to extract the distortion component, and further feeds out the extracted distortion component to cancel the distortion component in the output. This is based on the principle of removal or suppression.
[0004]
FIG. 1 shows a configuration of a distortion compensation amplifier including a distortion compensation circuit using a feedforward method. A signal input to the circuit in this figure is output to an antenna (not shown) through the main amplifier A1 and the delay circuit DL2. Since this input / output path is a path through which the signal to be amplified by the main amplifier A1 and the amplified signal pass, it can be called a main line. The directional coupler DC1 disposed in front of the main amplifier A1 supplies the input signal to the main amplifier A1 for amplification. On the other hand, the signal supplied to the main amplifier A1 is identical in frequency configuration but small in amplitude. The signal is branched and supplied to the directional coupler DC2 via the delay circuit DL1. The directional coupler DC2 supplies the output signal of the main amplifier A1 to the directional coupler DC3 via the delay circuit DL2, while the output signal of the main amplifier A1 is the same in terms of frequency configuration but has a small amplitude. The signal is branched and further combined with the signal supplied via the delay circuit DL1, and the extracted distortion signal generated thereby is supplied to the distortion amplifier A2. The directional coupler DC3 generates a distortion compensation output signal by combining the signal supplied via the delay circuit DL2 and the input from the distortion amplifier A2 with a predetermined gain, and outputs the distortion compensation output signal to an antenna or the like.
[0005]
Here, the delay time of the delay circuit DL1 configured by a coaxial delay line or the like is made to coincide with the delay time generated in the path on the main line from the directional coupler DC1 through the main amplifier A1 to the directional coupler DC2. Shall be kept. Further, a modulator M1 for adjusting the amplitude and phase of the signal or each of the I and Q component values is provided before or after the path on the main line or the delay circuit DL1. The modulator M1 is set or controlled so that carrier components in two types of signals coupled to each other by the directional coupler DC2 have the same amplitude and opposite phase. In that case, the extracted distortion signal output from the directional coupler DC2 to the distortion amplifier A2 side is generally a signal including only the distortion component generated due to the nonlinearity in the main amplifier A1. Therefore, a loop from the directional coupler DC1 to the directional coupler DC2, that is, a feedforward loop that delays the branched input signal by the delay circuit DL1 and supplies the delayed input signal to the directional coupler DC2 to generate the extracted distortion signal, This can be called a distortion extraction loop.
[0006]
Further, the delay time of the delay circuit DL2 constituted by a coaxial delay line or the like is made to coincide with the delay time generated in the path from the directional coupler DC2 through the distortion amplifier A2 to the directional coupler DC3. To do. Further, a modulator M2 for adjusting the amplitude and phase of the signal or each of the I and Q component values is provided before or after the path or the delay circuit DL2. The modulator M2 is set or controlled so that distortion components in two types of signals coupled to each other by the directional coupler DC3 have the same amplitude and opposite phase. In that case, the signal output as the distortion compensation output signal from the directional coupler DC3 is generally a signal from which the above-described distortion component is removed or suppressed. Therefore, a loop from the directional coupler DC2 to the directional coupler DC3, that is, a feedforward loop that amplifies the extracted distortion signal by the distortion amplifier A2 and supplies the amplified distortion signal to the directional coupler DC3 to generate a distortion compensation output signal. It can be called a removal loop.
[0007]
The control unit CTL controls the operation of the distortion extraction loop, particularly the adjustment operation in the modulator M1, so that the carrier component does not leak into the extracted distortion signal, and the distortion component, particularly the intermodulation distortion component, leaks into the distortion compensation output signal. The operation of the distortion removal loop, particularly the adjustment operation in the modulator M2, is controlled so as not to be output. The control by the control unit CTL is performed using, for example, a method of inserting a pilot signal and detecting it. Alternatively, other methods such as a synchronous detection technique as previously proposed by the applicant of the present application are used. In addition, the directional couplers DC1 to DC3 are realized by, for example, a hybrid circuit as illustrated. Modulators M1 and M2 are quadrature modulators, or variable gain amplifiers or variable attenuators and variable phase shifters.
[0008]
[Problems to be solved by the invention]
However, in practice, it is difficult to prevent leakage of the carrier component to the extracted distortion signal over the entire frequency band to be used.
[0009]
First, in the circuit shown in FIG. 1, adjustment of amplitude, phase, and the like is performed by the modulator M1 under the control of the control unit CTL so that the carrier component does not leak into the extracted distortion signal in the directional coupler DC2. To do. For example, the delay time of the delay circuit DL1 is set and the modulator M1 is controlled so that a carrier suppression amount of 40 dB at 1 GHz (that is, the ratio of the carrier component in the extracted distortion signal to the output of the main amplifier A1) is obtained. At this time, if an error τ occurs in the delay time in the delay circuit DL1, the delay time setting error τ appears as a phase control error 2πfτ. That is, even if the carrier component can be ideally canceled / suppressed at a specific frequency, the phase control error 2πfτ increases and the suppression amount decreases as the distance from the frequency increases.
[0010]
Therefore, even if the delay time in the delay circuit DL1 is set so that a carrier suppression amount of 40 dB can be obtained at 1 GHz, if a setting error τ of, for example, 60 psec occurs in the delay circuit DL1, it is 60 MHz away from it. At 1.06 GHz, for example, a carrier suppression amount of only about 36 dB can be obtained. That is, a carrier component that cannot be ignored leaks into the extracted distortion signal. The error τ of 60 psec is a slight electrical length of 18 mm in the case of the coaxial delay line, and often occurs when the delay circuit DL1 is configured by the coaxial delay line.
[0011]
As a result, if a sufficiently large carrier suppression amount is to be obtained over a sufficiently wide frequency band extending over several tens of MHz, the delay time setting error τ must be made very small. Further, the delay circuit DL1 and other members in or around the distortion extraction loop have temperature characteristics. This temperature characteristic also causes a decrease in the amount of carrier suppression.
[0012]
The present invention has been made to solve such a problem, and is capable of reliably suppressing the carrier component leaking into the extracted distortion signal over a wider frequency band than in the past. Rough setting of the delay time is allowed, the operation of the strain extraction loop is stabilized with respect to parameters such as temperature, and it is resistant to noise and can be pulled into the optimum operating state in a shorter time The purpose is to make it.
[0013]
[Means for Solving the Problems]
To achieve the above object, the present invention is output from (1) This main amplifier Ri by the nonlinearity of the amplifying an input signal is attached to the output to the main amplifier the main amplifier including a carrier component A distortion compensation circuit used for removing or suppressing a distortion component , (2) an extracted distortion signal by feedforwarding a signal branched from the input signal and combining it with a signal branched from the output signal of the main amplifier A distortion extraction loop that generates a distortion, a distortion removal loop that generates a distortion-compensated output signal by feeding forward the extracted distortion signal and coupling it to the output signal, and a signal adjustment operation in the distortion extraction loop and the distortion removal loop A control unit, so that leakage of a carrier component to the extracted distortion signal is suppressed, and leakage of a distortion component to the distortion compensation output signal is suppressed. In feedforward distortion compensating circuit for executing the control, (3) the distortion extracting loop the input signal to 2 minutes Toki, first directional coupler for supplying one of the signals branched into the main amplifier for amplification And a splitter that splits the other signal branched from the first directional coupler into two branches, and one signal branched from the distributor and the output signal of the main amplifier to combine the first extracted distortion signal. A second directional coupler that outputs the output signal of the main amplifier separately from the first extracted distortion signal, and the other signal branched from the distributor and the first extracted distortion signal are combined. A third directional coupler that outputs the second extracted distortion signal and a second one that adjusts the amplitude and phase of one of the two signals combined by the third directional coupler based on the control of the control unit. A modulator for a three-way coupler; And the distortion removal loop combines the output signal of the main amplifier output from the second directional coupler with the second extracted distortion signal and outputs the distortion compensation output signal. A coupler.
[0014]
Moreover, in the feedforward distortion compensation circuit according to the present invention, the distortion extraction loop has an amplitude and phase of one of the two signals combined by the second directional coupler based on the control of the control unit. And a second directional coupler modulator that adjusts the amplitude and phase of one of the two signals combined by the fourth directional coupler based on the control of the control unit. It is preferable to provide a modulator for the fourth directional coupler that is adjusted in this manner. In the feedforward distortion compensation circuit according to the present invention, the modulator for the second directional coupler, the modulator for the third directional coupler, and the modulator for the fourth directional coupler are signals to be processed. It is preferable that the quadrature modulator adjust the amplitude and phase of the signal to be processed by adjusting the I component value and the Q component value .
[0015]
The present invention also provides a distortion compensation circuit attached to a main amplifier that amplifies and outputs an input signal including a carrier component, and is used to remove or suppress the distortion component output from the main amplifier due to the nonlinearity of the main amplifier. A distortion extraction loop that feeds forward a signal branched from the input signal and combines it with a signal branched from the output signal of the main amplifier, and feeds forward the extracted distortion signal to A distortion removal loop that generates a distortion-compensated output signal by coupling to the output signal and a control unit that controls the signal adjustment operation in the distortion extraction loop and the distortion removal loop are provided to suppress leakage of carrier components to the extracted distortion signal. Feedforward in which the control unit executes the control so that leakage of distortion components to the distortion compensation output signal is suppressed. In the compensation circuit, the distortion extraction loop branches the input signal into two branches, and branches from the first directional coupler for supplying one of the branched signals to the main amplifier for amplification, and the first directional coupler. The other signal is branched into two at the first stage, and one of the signals branched from the previous stage is branched from the first stage and a plurality of distributors connected in cascade to branch to the next stage. A second directional coupler that combines a signal that is not present and the output signal of the main amplifier to output a first extracted distortion signal and that outputs the output signal of the main amplifier separately from the first extracted distortion signal; The first extraction distortion signal is input to the first stage, and the branch signal corresponding to the first stage and the first stage are provided corresponding to each signal at the branch end branched from the distributor at the stage subsequent to the distributor at the first stage. Combined with the extracted distortion signal and output from the previous stage A cascade connection directional coupler connected in cascade so that a branch signal corresponding to the next stage is coupled to the signal, and outputting a second extracted distortion signal from the cascade connection directional coupler in the final stage, The distortion removal loop includes an output directional coupler that combines the output signal of the main amplifier output from the second directional coupler and the second extracted distortion signal and outputs the distortion compensation output signal. It is characterized by that.
[0016]
In the feedforward distortion compensation circuit according to the present invention, two signals that are provided corresponding to the second directional coupler, the cascaded directional coupler, and the output directional coupler are coupled. It is preferable to provide a modulator that adjusts any one of the amplitude and phase based on the control of the control unit. In the feedforward distortion compensation circuit according to the present invention, each modulator adjusts the I component value and the Q component value of the signal to be processed, thereby adjusting the amplitude and phase of the signal to be processed. A modulator is preferred.
[0018]
The matter that has been a problem in the prior art, that is, the narrow frequency band that can obtain a sufficient amount of carrier suppression, is due to the phase frequency characteristics of the members constituting the distortion extraction loop. It was happening. In other words, since the distortion extraction loop is constituted by a single loop, the phase frequency characteristic of the generally steep gradient in the loop is directly the phase frequency characteristic of the entire distortion extraction loop, and as a result, sufficient carrier suppression is achieved. The frequency band from which the quantity can be obtained was also narrowed. On the other hand, in the present invention, by multiplexing a plurality of loops, even if the gradient of the phase frequency characteristic of each loop is as steep as in the prior art, the gradient of the phase frequency characteristic of the entire distortion extraction loop is gentle. Thus, the frequency band in which a sufficient carrier suppression amount can be obtained is expanded.
[0019]
As a result, it is possible to design and set a circuit constituting the distortion extraction loop, for example, a delay circuit roughly as compared with the prior art, and it is stable against temperature. Furthermore, carrier suppression amount per stage directional coupler is smaller than the carrier suppression amount in the coupling member of the prior art (directional coupler DC2), less affected by noise than in the prior art also optimum adjustment state The time required for pulling in is also shortened .
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the structure similar or corresponding to the prior art shown in FIG. 1, and the overlapping description is abbreviate | omitted.
[0021]
FIG. 2 shows a circuit configuration according to an embodiment of the present invention. This embodiment has a configuration in which a distributor D1, a delay circuit DL1A, a modulator M1A, a directional coupler DC2A, and a stabilizing amplifier A3 are added to the prior art shown in FIG. The distributor D1 distributes the signal branched from the main line by the directional coupler DC1 into two, one of which is directed to the directional coupler DC2 via the delay circuit DL1, and the other is directed to the direction via the delay circuit DL1A and the modulator M1A. Supplied to the sex coupler DC2A. That is, in the present embodiment, the directional coupler DC1 and the distributor D1 correspond to the branch member for N branch described above. N is set to 3.
[0022]
Further, the directional coupler DC2A is, for example, a hybrid, and is used for stabilization by combining a signal input via the delay circuit DL1A and the modulator M1A with a signal branched from the main line by the directional coupler DC2 and via the delay circuit DL1. The signal input via the amplifier A3 is combined. The directional coupler DC2A supplies the resulting signal as an extracted distortion signal to the distortion removal loop. That is, in this embodiment, the directional couplers DC2 and DC2A are provided as the N-1 stage coupling members described above.
[0023]
The delay time in the delay circuit DL1 is the signal delay in the path from the branch point in the directional coupler DC1 to the coupling point in the directional coupler DC2 via the modulator M1 and the main amplifier A1, and the directional coupler DC1. The signal delay in the path from the branch point to the coupling point in the directional coupler DC2 through the distributor D1 and the delay circuit DL1 is set to be equal. The delay time in the delay circuit DL1A is determined from the branch point in the directional coupler DC1 through the modulator M1, the main amplifier A1, the directional coupler DC2, and the stabilizing amplifier A3, and the coupling point in the directional coupler DC2A. And a signal delay in a path from a branch point in the directional coupler DC1 to a coupling point in the directional coupler DC2A via the distributor D1, the delay circuit DL1A, and the modulator M1A. It is set to be equal.
[0024]
The control unit CTL controls the modulator M1 so that the carriers in the signals coupled by the directional coupler DC2 have the same amplitude and opposite phase. The control unit CTL controls the modulator M1A so that the carriers in the signal combined by the directional coupler DC2A have the same amplitude and opposite phase. The modulator M1A may have the same circuit configuration as the modulator M1. As a method of controlling the modulators M1 and M1A by the control unit CTL, various methods such as diverting the control method of the modulator M1 in the prior art can be adopted.
[0025]
In the prior art, unless the delay time in the delay circuit DL1 is set precisely, a sufficient carrier suppression amount cannot be obtained in the frequency band in which the amplifier is used. One of the advantages of the present embodiment is that the frequency band in which a sufficient carrier suppression amount can be obtained can be expanded without setting the delay times in the delay circuits DL1 and DL1A so precisely. That is, if the distortion extraction loop is doubled as in the present embodiment, the phase frequency characteristics of each loop constituting the distortion extraction loop may have a gradient similar to that of the distortion extraction loop in the prior art. The gradient of the phase frequency characteristic in the entire distortion extraction loop becomes gentle. As a result, a frequency band in which carrier suppression by coupling under amplitude / phase adjustment sufficiently works, that is, a frequency band in which the amount of carrier suppression in the distortion extraction loop is sufficiently large is widened. In other words, even if the delay time setting is rough compared to the conventional case, it is possible to suitably suppress the carrier over a frequency band equal to or higher than the conventional case.
[0026]
Further, by using the multiplexed strain extraction loop in this way, it becomes strong against changes in delay time due to environmental changes including temperature changes. In addition, since the amplitude / phase adjustment amount in the N−1 loops constituting the distortion extraction loop is reduced when viewed per loop, the control by the control unit CTL becomes more stable, and the optimum operation state is achieved. The pull-in is also accelerated. In particular, by amplifying a signal supplied from the directional coupler DC2 to the directional coupler DC2A and increasing its level, a distortion extraction loop that is strong against noise and more stable can be obtained.
[0027]
Note that the circuit shown in FIG. 2 is only one embodiment of the present invention. The present invention can also be implemented as a circuit in which various modifications are made to the circuit shown in FIG. For example, the stabilizing amplifier A3 in FIG. 2 can be omitted if sufficient stability can be obtained without it. Further, although N = 3 in FIG. 2, N = 4 may be used as shown in FIG. In FIG. 3, D2 is a distributor having the same configuration as the distributor D1, DL1B is a delay circuit, M1B is a modulator, DC2B is a directional coupler, A4 is a stabilizing amplifier, and the control unit CTL is a modulator. It also controls M1B. As with the stabilizing amplifier A3, the stabilizing amplifier A4 can be omitted. Of course, it is also possible to set N> 4. Further, the modulator M1 may be moved to the delay circuit DL1 side as shown in FIG. The delay circuits DL1 and DL1A may be moved as indicated by symbols X1 to X4 in FIG. A part or all of the delay circuits DL1 and DL1A can be combined into one delay circuit. The N-1 loops constituting the distortion extraction loop have the maximum carrier suppression amount in any one of the frequencies in the frequency band in which the amplifier is used, that is, the frequency band in which carriers are distributed. ,design. It is not necessary to make the frequency with the maximum carrier suppression amount exactly between the loops.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a circuit according to a conventional technique.
FIG. 2 is a block diagram showing a configuration of a circuit according to an embodiment of the present invention.
FIG. 3 is a block diagram showing a modification of this embodiment, particularly a distortion extraction loop portion thereof.
FIG. 4 is a block diagram showing another modification of this embodiment, in particular, its modulator arrangement.
FIG. 5 is a block diagram showing still another modification of this embodiment, in particular, a delay circuit arrangement thereof;
[Explanation of symbols]
A1 main amplifier, A2 distortion amplifier, A3, A4 stabilization amplifier, CTL control unit, D1, D2 distributor, DC1 to DC3, DC2A, DC2B directional coupler, DL1, DL1A, DL1B, DL2 delay circuit, M1, M1A, M1B, M2 modulator.

Claims

A distortion compensation circuit that is attached to a main amplifier that amplifies and outputs an input signal including a carrier component and is used to remove or suppress a distortion component output from the main amplifier due to nonlinearity of the main amplifier,
A distortion extraction loop that generates an extracted distortion signal by feed-forwarding a signal branched from the input signal and combining it with a signal branched from the output signal of the main amplifier, and feed-forwarding the extracted distortion signal and coupling it to the output signal A distortion removal loop that generates a distortion-compensated output signal, and a distortion extraction loop and a control unit that controls a signal adjustment operation in the distortion removal loop, so that leakage of carrier components to the extracted distortion signal is suppressed. In the feedforward distortion compensation circuit in which the control unit performs the control so that leakage of distortion components to the distortion compensation output signal is suppressed,
The distortion extraction loop is
A first directional coupler for bifurcating the input signal and supplying one of the branched signals to the main amplifier for amplification;
A distributor for branching the other signal branched from the first directional coupler;
A second signal that combines one of the signals branched from the distributor and the output signal of the main amplifier to output a first extracted distortion signal and outputs an output signal of the main amplifier separately from the first extracted distortion signal A directional coupler;
A third directional coupler for combining the other signal branched from the distributor and the first extracted distortion signal and outputting a second extracted distortion signal;
A modulator for a third directional coupler that adjusts the amplitude and phase of one of the two signals combined by the third directional coupler based on the control of the control unit;
With
The distortion removal loop is
A fourth directional coupler for combining the output signal of the main amplifier output from the second directional coupler and the second extracted distortion signal to output the distortion compensation output signal;
A feedforward distortion compensation circuit comprising:

The feedforward distortion compensation circuit according to claim 1,
The distortion extraction loop is
A modulator for a second directional coupler that adjusts the amplitude and phase of one of the two signals combined by the second directional coupler based on the control of the control unit;
The distortion removal loop is
A feedforward comprising a modulator for a fourth directional coupler that adjusts the amplitude and phase of one of two signals combined by the fourth directional coupler based on control of the control unit. Distortion compensation circuit.

The feedforward distortion compensation circuit according to claim 2,
The second directional coupler modulator, the third directional coupler modulator, and the fourth directional coupler modulator are:
A feedforward distortion compensation circuit, which is a quadrature modulator that adjusts the amplitude and phase of a signal to be processed by adjusting an I component value and a Q component value of the signal to be processed.

A distortion compensation circuit that is attached to a main amplifier that amplifies and outputs an input signal including a carrier component and is used to remove or suppress a distortion component output from the main amplifier due to nonlinearity of the main amplifier,
A distortion extraction loop that generates an extracted distortion signal by feed-forwarding a signal branched from the input signal and combining it with a signal branched from the output signal of the main amplifier, and feed-forwarding the extracted distortion signal and coupling it to the output signal A distortion removal loop that generates a distortion-compensated output signal, and a distortion extraction loop and a control unit that controls a signal adjustment operation in the distortion removal loop, so that leakage of carrier components to the extracted distortion signal is suppressed. In the feedforward distortion compensation circuit in which the control unit performs the control so that leakage of distortion components to the distortion compensation output signal is suppressed,
The distortion extraction loop is
A first directional coupler for bifurcating the input signal and supplying one of the branched signals to the main amplifier for amplification;
A plurality of distributors connected in cascade so that the other signal branched from the first directional coupler is branched into two at the first stage and one signal branched from the previous stage is branched into two at the next stage;
One of the signals branched from the first-stage distributor and not led to the next stage is combined with the output signal of the main amplifier to output the first extracted distortion signal, and the main extracted signal is separated from the first extracted distortion signal. A second directional coupler for outputting an output signal of the amplifier;
Provided corresponding to each signal at the branch end branched from the distributor at the stage subsequent to the distributor at the first stage, the first extracted distortion signal is input to the first stage, and the branch signal and the first extraction corresponding to the first stage are provided. A cascade connection directional coupler that is coupled in a cascade manner so that a distorted signal is coupled and a branch signal corresponding to the next stage is coupled to the signal output from the previous stage;
With
The second extracted distortion signal is output from the cascaded directional coupler at the final stage,
The distortion removal loop is
An output directional coupler that combines the output signal of the main amplifier output from the second directional coupler and the second extracted distortion signal to output the distortion compensation output signal;
A feedforward distortion compensation circuit comprising:

The feedforward distortion compensation circuit according to claim 4 ,
The control unit controls the amplitude and phase of one of two signals to be combined corresponding to the second directional coupler, the cascaded directional coupler, and the output directional coupler. A feedforward distortion compensation circuit comprising a modulator that adjusts based on

The feedforward distortion compensation circuit according to claim 5 ,
Each modulator is
A feedforward distortion compensation circuit, which is a quadrature modulator that adjusts the amplitude and phase of a signal to be processed by adjusting an I component value and a Q component value of the signal to be processed.