JP2004048500A

JP2004048500A - Communication system

Info

Publication number: JP2004048500A
Application number: JP2002204731A
Authority: JP
Inventors: Naoki Umeda; 梅田　直樹; Hideo Sakamoto; 阪本　英雄; Mitsuharu Ikeda; 池田　光治
Original assignee: Matsushita Electric Works Ltd
Current assignee: Panasonic Electric Works Co Ltd
Priority date: 2002-07-12
Filing date: 2002-07-12
Publication date: 2004-02-12
Anticipated expiration: 2022-07-12
Also published as: JP3963132B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication system having a collision detecting function capable of increasing both the maximum transmission distance and the number of branch connections. <P>SOLUTION: This communication system consists of a plurality of communication terminals 1, a branch unit 2 and a balanced two-wire cable C1 so that the communication terminals 1 can transmit and receive data signals with each other through the branch unit 1 and the balanced two-wire cable C1. The branch unit 2 is provided with a pair of feed terminal parts 2a and 2b for connecting the to the balanced two-wire cable C1, and a branch terminal part 2c for connecting branch unit 2 through the balanced two-wire cable C2 to the communication terminal 1, and a branch circuit part 2d. The branch circuit part 2d is configured to connect branch points with a high impedance so that the attenuation of a modulated wave signal transmitted from the other feed terminal is made smaller with respect to a modulated wave signal incoming to one of the feed terminal parts 2a and 2b, and that the impedance of the branch terminal part 2c can be made equal to the characteristic impedance of the transmission path of the modulated wave signal. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、データ信号の送受信を行う通信システムに関するものである。
【０００２】
【従来の技術】
図９は従来の一般的な通信システムの一構成例を示す図である。この図に示す通信システムは、複数の通信端末１００と、これらの各通信端末１００に分岐接続される平衡２線ケーブル（ペア線）Ｃとにより構成され、複数の通信端末１００が平衡２線ケーブルＣを介して相互にデータ信号を送受信するようになっている。
【０００３】
通信端末１００は、平衡２線ケーブルＣで当該通信端末１００を他の通信端末１００と接続するための端子部１００ｉと、データ信号の送信及び受信などの各種処理を実行するＣＰＵ部１００ｆと、このＣＰＵ部１００ｆからの送信するべきデータ信号から被変調波信号を生成し、これを端子部１００ｉから他の通信端末１００に送信する信号送信部１００ｂと、信号送信部１００ｂが送信した自らの被変調波信号を受信し、これを復調して得られるデータ信号を信号衝突検出部１００ｅに出力する送信信号受信部１００ｃと、端子部１００ｉに入来する平衡２線ケーブルＣからの被変調波信号を受信し、これを復調して得られるデータ信号をＣＰＵ部１００ｆおよび信号衝突検出部１００ｅに出力する伝送信号受信部１００ｄと、送信信号受信部１００ｃと伝送信号受信部１００ｄとが受信して得られた夫々のデータ信号を比較することにより平衡２線ケーブルＣ上のデータ信号の衝突を検出する信号衝突検出部と、信号送信部１００ｂの出力および伝送信号受信部１００ｄの入力と端子部１００ｉとの間に介設される２線４線変換回路１００ａと、交流電源の交流電力を直流電力に変換する電源部１００ｇと、この電源部１００ｇで変換された直流電力から駆動電力を生成して各部に供給する内部電源１００ｈとを備えている。
【０００４】
このような通信システムでは、通信端末１００の信号送信部１００ｂでデータ信号および搬送波信号から被変調波信号が生成され、２線４線変換回路１００ａを経由して平衡２線ケーブルＣ上に送信される。送信された被変調波信号は、別の通信端末１００に受信され、その伝送信号受信部１００ｄで復調され、元のデータ信号に復号される。
【０００５】
ここで、平衡２線ケーブルＣ上の伝送信号の周波数については、上りと下りとで同一の周波数帯域が使用される。配線形態は任意の箇所で分岐が可能なマルチドロップであり、分岐点では直接平衡２線ケーブルＣ同士が結ばれる。
【０００６】
このような通信方式の場合、複数の通信端末１００が同時に送信すると、平衡２線ケーブルＣに送信された信号が衝突し、何れの通信端末１００においても通信相手の信号を正常に受信することができなくなる。このため、一般的に、各通信端末１００は、送信前に、伝送信号受信部１００ｄで受信されるデータ信号を監視することにより、平衡２線ケーブルＣ上に送信中の信号が有るか無いかを検出することになっている。そして、平衡２線ケーブルＣ上に送信中の信号が有ることを検出した場合には、送信時点を延期し、再度検出を行って送信中の信号が無ければ送信を行うように送信タイミングの調整が行われるようになっている。
【０００７】
また、通信装置１００は、被変調波信号の送信中には、信号衝突検出部１００ｅにてデータ信号が正常に送信されているのか、他の通信装置１００から送信されたデータ信号と衝突していないのかを検出している。つまり、伝送信号受信部１００ｄと送信信号受信部１００ｃとのデータ信号が一致した場合には、平衡２線ケーブルＣ上に伝送されている信号は１つであり信号の衝突は起こっていないと判断し、一致しない場合には、平衡２線ケーブルＣ上に伝送されている信号は複数あり、信号の衝突が起こっていると判断する。データ信号の衝突を検出した場合には、送信中の被変調波信号を停止させ、時間をおいて再び被変調波信号の送信を試みる。
【０００８】
【発明が解決しようとする課題】
しかしながら、上記従来の通信システムでは、信号の衝突を回避しつつ信号の送受信を好適に行うことができるものの、平衡２線ケーブルＣの分岐点ｘでは、直接ケーブル同士が接続されるために、その分岐点ｘで平衡２線ケーブルのインピーダンスが低下してしまい、伝送信号である被変調波信号が減衰および反射するという問題があった。また、これにより、被変調波信号の振幅が小さくなり、被変調波信号が大きな歪みを持つようになると、データ信号の復調が不可能となり、伝送距離および分岐接続数の両最大値を増加することができない。
【０００９】
本発明は上記問題点に鑑みて為されたものであって、その目的とするところは、衝突検出機能を有した通信システムにおいて、伝送距離および分岐接続数の両最大値を増加することができる通信システムを提供することにある。
【００１０】
【課題を解決するための手段】
上記目的を達成するために、請求項１の発明は、複数の通信端末と、これらの各通信端末に接続される分岐器と、これらの各分岐器間に接続される平衡２線ケーブルとにより構成され、前記複数の通信端末が前記分岐器および前記平衡２線ケーブルを介して相互にデータ信号を送受信する通信システムであって、前記通信端末は、送信するべきデータ信号から被変調波信号を生成し前記平衡２線ケーブルに送信する信号送信部と、その信号送信部が送信した自らの被変調波信号を受信しこれを復調してデータ信号を得る送信信号受信部と、前記平衡２線ケーブルからの被変調波信号を受信しこれを復調してデータ信号を得る伝送信号受信部と、前記送信信号受信部と前記伝送信号受信部とが受信し復調して得られた夫々のデータ信号を比較することにより前記平衡２線ケーブル上のデータ信号の衝突を検出する信号衝突検出部とを備え、前記分岐器は、前記平衡２線ケーブルと接続するための一対の送り端子部と、当該分岐器を前記通信端末に接続するための分岐端子部と、分岐回路部を含み、前記分岐回路部は、前記一対の送り端子部間の両ラインと前記分岐端子部との間に介設され前記平衡２線ケーブルに対してハイインピーダンスとなる一対の抵抗と、これら一対の抵抗と前記分岐端子部との間に介設され前記平衡２線ケーブルとインピーダンス整合をとるためのトランスとにより構成されるものとした。
【００１１】
請求項２の発明は、請求項１記載の発明において、前記分岐器は、前記送り端子部からの被変調波信号を増幅する受信信号増幅器と、前記分岐端子部からの被変調波信号を増幅する送信信号増幅器と、第１の入出力端子から入力された被変調波信号を分配して第２，第３の入出力端子から出力し、第２，第３の入出力端子から入力された被変調波信号を混合して前記第１の入出力端子から出力する２つのハイブリッド回路とを有し、一方の前記ハイブリッド回路の第１の入出力端子を前記分岐回路部と前記分岐端子部との間で前記分岐回路部側に接続し、他方のハイブリッド回路の第１の入出力端子を前記分岐回路部と前記分岐端子部との間で前記分岐端子部側に接続し、２つの前記ハイブリッド回路の第２，第３の入出力端子間を、前記受信信号増幅器と前記送信信号増幅器とで接続したものとした。
【００１２】
請求項３の発明は、請求項１記載の発明において、前記通信端末は、第１の入出力端子から入力された被変調波信号を分配して第２，第３の入出力端子から出力し第２，第３の入出力端子から入力された被変調波信号を混合して前記第１の入出力端子から出力するハイブリッド回路を有し、前記ハイブリッド回路の第１の入出力端子を前記平衡２線ケーブルと接続し、前記ハイブリッド回路の第２の入出力端子と前記信号送信部との間に、前記信号送信部からの被変調波信号を増幅する送信信号増幅器を接続し、前記ハイブリッド回路の第３の入出力端子と前記伝送信号受信部との間に、前記平衡２線ケーブルからの被変調波信号を増幅する受信信号増幅器を接続して構成され、前記送信信号増幅器と前記受信信号増幅器は、合わせて、前記ハイブリッド回路における逆結合減衰量分だけ被変調波信号を増幅させるものとした。
【００１３】
請求項４の発明は、請求項１記載の発明において、前記通信端末は、第１の入出力端子から入力された被変調波信号を分配して第２，第３の入出力端子から出力し第２，第３の入出力端子から入力された被変調波信号を混合して前記第１の入出力端子から出力するハイブリッド回路を有し、前記ハイブリッド回路の第１の入出力端子を前記平衡２線ケーブルと接続し、前記ハイブリッド回路の第２の入出力端子と前記信号送信部との間に、前記信号送信部からの被変調波信号を増幅する送信信号増幅器を接続し、前記ハイブリッド回路の第３の入出力端子と前記伝送信号受信部とを接続して構成され、前記送信信号増幅器は、前記ハイブリッド回路における逆結合減衰量分だけ被変調波信号を増幅させるものとした。
【００１４】
【発明の実施の形態】
以下、本発明を実施形態１から実施形態４によって説明する。
（実施形態１）
図１は本発明に係る第１実施形態の通信システムの構成例を示す図、図２は同通信システムにおける通信端末の構成図、図３は同通信システムにおける分岐器の構成図である。
【００１５】
第１実施形態の通信システムは、図１に示すように、複数の通信端末１と、これらの各通信端末１に接続される分岐器２と、これらの各分岐器２間に接続される平衡２線ケーブルＣ１とにより構成され、複数の通信端末１が分岐器２および平衡２線ケーブルＣ１を介して相互にデータ信号を送受信するようになっている。
【００１６】
通信端末１は、図２に示すように、平衡２線ケーブルＣ２を介して直下の（当該通信端末１に接続される）分岐器２と接続される端子部１ｉと、データ信号の送信および受信などの各種処理を実行するＣＰＵ部１ｆと、このＣＰＵ部１ｆからの送信するべきデータ信号から被変調波信号を生成し、これを直下の分岐器２経由で他の通信端末１に送信する信号送信部１ｂと、信号送信部１ｂが送信した自らの被変調波信号を受信し、これを復調して得られるデータ信号を信号衝突検出部１ｅに出力する送信信号受信部１ｃと、端子部１ｉに入来する平衡２線ケーブルＣ１，Ｃ２からの被変調波信号を受信し、これを復調して得られるデータ信号をＣＰＵ部１ｆおよび信号衝突検出部１ｅに出力する伝送信号受信部１ｄと、送信信号受信部１ｃと伝送信号受信部１ｄとが受信し復調して得られた夫々のデータ信号を比較することにより平衡２線ケーブルＣ１，Ｃ２上のデータ信号の衝突を検出する信号衝突検出部１ｅと、信号送信部１ｂの出力および伝送信号受信部１ｄの入力と端子部１ｉとの間に介設される２線４線変換回路１ａと、交流電源の交流電力を直流電力に変換する電源部１ｇと、この電源部１ｇで変換された直流電力から駆動電力を生成して各部に供給する内部電源１ｈとを備えている。
【００１７】
分岐器２は、図３に示すように、平衡２線ケーブルＣ１と接続するための一対の送り端子部２ａ，２ｂと、平衡２線ケーブルＣ２を介して当該分岐器２を通信端末１に接続するための分岐端子部２ｃとを備えているほか、分岐回路部２ｄを備えている。
【００１８】
尚、送り端子部２ａの端子２０，２１および送り端子部２ｂの端子２２，２３は、それぞれ、分岐器２の内部で互いに電気的に接続されている。
【００１９】
分岐回路部２ｄは、一対の送り端子部２ａ，２ｂのうち一方の送り端子部に入来する被変調波信号に対して、他方の送り端子部から送出される被変調波信号の減衰が少なくなるように、分岐点を高インピーダンスで接続し、分岐端子部２ｃのインピーダンスが被変調波信号の伝送線路の特性インピーダンスに等しくなるように構成される。則ち、一対の送り端子部２ａ，２ｂ間の両ラインＬＮ１，ＬＮ２と分岐端子部２ｃとの間に介設され平衡２線ケーブルＣ１に対してハイインピーダンスとなる一対の抵抗Ｒ１，Ｒ２と、これらの抵抗Ｒ１，Ｒ２と両ラインＬＮ１，ＬＮ２との間に直列に介設される一対のコンデンサＣ１，Ｃ２と、一対の抵抗Ｒ１，Ｒ２と分岐端子部２ｃとの間に介設され平衡２線ケーブルＣ２とインピーダンス整合をとるためのトランスＴ１と、このトランスＴ１と分岐端子部２ｃとの間に介設される一対のコンデンサＣ３，Ｃ４とにより構成される。
【００２０】
コンデンサＣ１，Ｃ２，Ｃ３，Ｃ４は、低周波成分の通過を阻止するために設けられる。抵抗Ｒ１，Ｒ２は、平衡２線ケーブルＣ１の特性インピーダンスよりも十分に大きいインピーダンス値を有し、分岐点での平衡２線ケーブルＣ１の特性インピーダンスに影響を与えずに、被変調波信号を分岐端子部２ｃに伝達する役目を担う。トランスＴ１は、分岐端子部２ｃ側からみた特性インピーダンスが平衡２線ケーブルＣ１の特性インピーダンスと等しくなるように巻き数比が調整されている。尚、終端となる分岐器２における一方の送り端子部には、コンデンサおよび抵抗からなる終端部材Ｚが接続される。
【００２１】
このように構成される通信システムでは、通信端末１の信号送信部１ｂでデータ信号および搬送波信号から被変調波信号が生成され、２線４線変換回路１ａおよび平衡２線ケーブルＣ２を経由して分岐器２の分岐端子部２ｃに送信される。その送信された被変調波信号は、分岐回路部２ｄを介して一対の送り端子部２ａ，２ｂに伝達され、そこからそれぞれの平衡２線ケーブルＣ１上に送信されて、別の両分岐器２に伝送される。
【００２２】
別の両分岐器２の各々において、一方の送り端子部に入来した上記被変調波信号は、他方の送り端子部からさらに別の分岐器２に伝送されていく。このようにして上記被変調波信号が他の全ての分岐器２に伝送される。
【００２３】
これらの各分岐器２において、一方の送り端子部に入来した上記被変調波信号は、分岐回路部２ｄを介して分岐端子部２ｃに伝達され、そこからその平衡２線ケーブルＣ２上に送信されて、他の通信端末１に送られる。
【００２４】
他の通信端末１では、被変調波信号が伝送信号受信部１ｄで復調され、元のデータ信号に復号される。
【００２５】
要するに、各分岐器２において、分岐端子部２ｃに入った被変調波信号は、一対の送り端子部２ａ，２ｂの各々から出力し、一方の送り端子部に入った被変調波信号は、他方の送り端子部および分岐端子部２ｃから出力し、他方の送り端子部に入った被変調波信号は、一方の送り端子部および分岐端子部２ｃから出力するのである。
【００２６】
かかる通信システムによれば、分岐器２において平衡２線ケーブルＣ１のインピーダンス整合が保たれ、しかも高インピーダンスで被変調波信号が分岐されるので、被変調波信号の分岐点における挿入損失を低減することができ、伝送距離および分岐接続数の両最大値を増加することができる。
【００２７】
（実施形態２）
本実施形態における通信システムの基本構成は、実施形態１と同様であり、実施形態１と共通する部分については同一の符号を付して説明を省略し、本実施形態の特徴となる部分についてのみ詳細に説明する。
【００２８】
本実施形態の通信システムは、実施形態１の通信システムと比較して、通信端末１および分岐器２に代えて、図４および図５に夫々示した、通信端末１Ａおよび分岐器２Ａとを備えた点に特徴がある。
【００２９】
通信端末１Ａは、図４に示すように、２線４線変換回路１ａと、信号送信部１ｂと、送信信号受信部１ｃと、伝送信号受信部１ｄと、信号衝突検出部１ｅと、ＣＰＵ１ｆと、電源部１ｇと、内部電源１ｈと、端子部１ｉとを実施形態１の通信端末１と同様に備えているほか、通信端末１との相違点として、ＤＣ電源重畳部１ｊとを備えている。
【００３０】
ＤＣ電源重畳部１ｊは、２線４線変換回路１ａと端子部１ｉとの間に介設され、電源部１ｇから直流電力を得て、直下の分岐器２Ａ用にＤＣ電源を確保するための直流電力を端子部１ｉから出力するものである。
【００３１】
分岐器２Ａは、図５に示すように、送り端子部２ａ，２ｂと、分岐端子部２ｃと、分岐回路部２ｄとを実施形態１の分岐器２と同様に備えているほか、分岐器２との相違点として、第１のハイブリッド回路２ｅと、第２のハイブリッド回路２ｆと、受信信号増幅器２ｇと、送信信号増幅器２ｈと、ＤＣ電源分離部２ｉと、内部電源２ｊとを備えている。
【００３２】
第１，第２のハイブリッド回路２ｅ，２ｆは、夫々の第１の入出力端子部２４，２７から入力された被変調波信号を分配して夫々の第２の入出力端子部２５，２８と第３の入出力端子部２６，２９とから出力し、また夫々の第２，第３の入出力端子部から入力された被変調波信号を混合して夫々の第１の入出力端子部２４，２７から出力する。第１のハイブリッド回路２ｅの第１の入出力端子部２４は、分岐回路部２ｄと分岐端子部２ｃとの間の分岐回路部２ｄ側に接続され、第２のハイブリッド回路２ｆの第１の入出力端子部２７は、分岐回路部２ｄと分岐端子部２ｃとの間の分岐端子部２ｃ側に接続される。夫々のハイブリッド回路の第２の入出力端子部２５，２８間には、送信信号増幅器２ｈが接続され、第３の入出力端子部２６，２９間には、受信信号増幅器２ｇが接続される。
【００３３】
送信信号増幅器２ｈは、分岐端子部２ｃからの被変調波信号を増幅するためのものであり、受信信号増幅器２ｇは、送り端子部２ａ，２ｂからの被変調波信号を増幅するためのものである。
【００３４】
ＤＣ電源分離部２ｉは、第２のハイブリッド回路２ｆと分岐端子部２ｃとの間に接続され、通信端末１Ａからの被変調波信号および直流電力からそれぞれを分離し、被変調波信号を第２のハイブリッド回路２ｆに伝達する一方、直流電力を内部電源２ｊに供給するものである。
【００３５】
内部電源２ｊは、ＤＣ電源分離部２ｉから供給される直流電力により当該分岐器２Ａの各部に必要な電力を供給するものである。
【００３６】
ここで、図６を用いて第１，第２のハイブリッド回路についてさらに詳説する。第１のハイブリッド回路２ｅは、トランスＴ２〜５と抵抗Ｒ３，Ｒ４とからなり、第１の入出力端子部２４の各端子には、並列結合されたトランスＴ２，Ｔ３が接続されている。第２の入出力端子部２５の一方の端子は、トランスＴ４及び抵抗Ｒ３の一端と接続され、第２の入出力端子部２５の他方の端子は、トランスＴ５及び抵抗Ｒ４の一端と接続されている。第３の入出力端子部２６の一方の端子は、トランスＴ４及び抵抗Ｒ３の他端と接続され、第３の入出力端子２６の他方の端子は、トランスＴ５及び抵抗Ｒ４の他端と接続されている。
【００３７】
第２のハイブリッド回路２ｆも同様に、トランスＴ６〜９と抵抗Ｒ５，Ｒ６とからなり、第１の入出力端子部２７の各端子は、並列結合されたトランスＴ８，Ｔ９と接続され、第２の入出力端子部２８の一方の端子はトランスＴ６及び抵抗Ｒ５の一端と、第２の入出力端子部２８の他方の端子はトランスＴ７及び抵抗Ｒ６の一端と、第３の入出力端子部２９の一方の端子はトランスＴ７及び抵抗Ｒ６の他端と、第３の入出力端子部２９の他方の端子はトランスＴ６及び抵抗Ｒ５の他端と夫々接続されている。
【００３８】
ここで抵抗Ｒ３〜Ｒ６は増幅器接続側の出力インピーダンスを決定するための抵抗であると共に、アンバランス分の電力を吸収する。トランスＴ４〜Ｔ７は信号を２つに分配或いは２つの信号を１つに混合させる役割をしている。またトランスＴ２，Ｔ３は第１のハイブリッド回路２ｅの第１の入出力端子部２４の、トランスＴ８，Ｔ９は第２のハイブリッド回路２ｆの第１の入出力端子部２７のインピーダンス整合を取るためのものであり、整合が取れるように巻き数比を夫々調整している。
【００３９】
上記のように構成されたハイブリッド回路において、第１のハイブリッド回路２ｅの第１の入出力端子部２４から入力された被変調波信号は、等しく２つの信号成分に分配され、第２の入出力端子部２５と第３の入出力端子部２６へと出力される。
【００４０】
第３の入出力端子部２６へ出力された信号成分は、順方向に接続された受信信号増幅器２ｇの利得によって増幅され、第２のハイブリッド回路２ｆの第３の入出力端子部２９へ入力される。
【００４１】
一方、第２の入出力端子部２５には、逆方向に接続された送信信号増幅器２ｈが接続されているため、第２の入出力端子部２５から出力された信号成分は、第２のハイブリッド回路２ｆの第２の入出力端子部２８へ透過することはない。
【００４２】
第２のハイブリッド回路２ｆの第３の入出力端子部２９に入力された被変調波信号は、再び第２のハイブリッド回路２ｆを経由して第２のハイブリッド回路２ｆの第１の入出力端子２７から出力される。
【００４３】
この時、第２のハイブリッド回路２ｆの第３の入出力端子部２９と第２の入出力端子部２８との間には、逆結合減衰量が存在するため、第３の入出力端子部２９に入力された信号成分が第２の入出力端子部２８に漏れ出す量は極僅かとなる。ただし、信号の発振を防ぐために、ハイブリッド回路１つ当たりの逆結合減衰量が−Ａ［ｄＢ］の場合、受信信号増幅器２ｇと送信信号増幅器２ｈとの利得合計は２Ａ［ｄＢ］を越えてはならない。
【００４４】
同様に、第２のハイブリッド回路２ｆの第１の入出力端子部２７から入力された被変調波信号は、第２のハイブリッド回路２ｆによって分配され、第２の入出力端子部２８から出力した信号成分が送信信号増幅器２ｈの利得によって増幅された後、第１のハイブリッド回路２ｅの第１の入出力端子部２４から出力される。
【００４５】
かかる通信システムにおいては、分岐器２Ａ内で被変調波信号の双方向増幅が可能となり、通信端末１Ａから送信される被変調波信号を適切なレベルで他の通信端末１Ａに伝送することができると共に、他の通信端末１Ａからの被変調波信号を適切なレベルで受信することができ、実施形態１よりさらに通信システム全体の伝送距離および分岐接続数の両最大値を増加することができる。
【００４６】
（実施形態３）
本実施形態における通信システムの基本構成は、実施形態１又は実施形態２と同様であり、それらと共通する部分については同一の符号を付して説明を省略し、本実施形態の特徴となる部分についてのみ詳細に説明する。
【００４７】
本実施形態の通信システムは、実施形態１の通信端末１に代えて、図７に示した通信端末１Ｂを備えた点に特徴がある。分岐器２の構成は、実施形態１と同様である。
【００４８】
通信端末１Ｂは、信号送信部１ｂと、送信信号受信部１ｃと、伝送信号受信部１ｄと、信号衝突検出部１ｅと、ＣＰＵ１ｆと、電源部１ｇと、内部電源１ｈと、端子部１ｉとを実施形態１の通信端末１と同様に備えているほか、通信端末１との相違点として、２線４線変換回路１ａを省いて、ハイブリッド回路１ｋと、送信信号増幅器１ｌと、受信信号増幅器１ｍとを備えている。
【００４９】
ハイブリッド回路１ｋと、送信信号増幅器１ｌと、受信信号増幅器１ｍとは、夫々実施形態２のハイブリッド回路２ｅと送信信号増幅器２ｈと受信信号増幅器２ｇと同様のものであり、本実施形態は、実施形態２のハイブリッド回路２ｅと送信信号増幅器２ｈと受信信号増幅器２ｇとを、分岐器内部から通信端末内部へ移動させたものに相当する。
【００５０】
ハイブリッド回路１ｋの第１の入出力端子部１０は、端子部１ｉに接続され、第２の入出力端子部１１は、送信信号増幅器１ｌの出力端と接続され、第３の入出力端子部１２は、受信信号増幅器１ｍの入力端と接続される。
【００５１】
送信信号増幅器１ｌは、その入力端が抵抗Ｒを介して信号送信部１ｂと接続され、信号送信部１ｂからの被変調波信号を増幅する。受信信号増幅器１ｍは、その出力端が伝送信号受信部１ｄと接続され、端子部１ｉに入来した被変調波信号を増幅して伝送信号受信部１ｄへ入力する。
【００５２】
このように構成される通信システムでは、信号送信部１ｂから送信された被変調波信号は、送信信号増幅器１ｌによって増幅され、ハイブリッド回路１ｋを介して、端子部１ｉから平衡２線ケーブルＣ２上に送信される。
【００５３】
また、平衡２線ケーブルＣ２から端子部１ｉに入来した被変調波信号は、ハイブリッド回路１ｋによって、等しく２つの信号成分に分配され、第２，第３の入出力端子部１１，１２から出力される。第３の入出力端子部１２から出力された信号成分は、順方向に接続された受信信号増幅器１ｍによって増幅された後、伝送信号受信部１ｄへ入力される。一方、第２の入出力端子部１１には逆方向に接続された送信信号増幅器１ｌが接続されているため、第２の入出力端子部１１から出力された信号成分が信号送信部１ｂへ透過することはない。
【００５４】
ここで、送信信号増幅器１ｌと受信信号増幅器１ｍの利得について説明する。信号衝突検出部１ｅは、データ信号の送信中に伝送信号受信部１ｄが受信する信号と送信信号受信部１ｃが受信する自身の送信した信号とを比較し、一致した場合には、平衡２線ケーブルＣ上に伝送されている信号は１つであり信号の衝突は起こっていないと判断し、一致しない場合には、平衡２線ケーブルＣ上に伝送されている信号は複数あり、信号の衝突が起こっていると判断する。よって、衝突検出機能を正常に働かせるためには、送信信号受信部１ｃと伝送信号受信部１ｄとが受信する信号レベルが同一である必要がある。
【００５５】
ここで、信号送信部１ｂと送信信号増幅器１ｌとの間に設置された抵抗Ｒでの減衰量を−ｒ［ｄＢ］、送信信号増幅器１ｌの利得をα［ｄＢ］、受信信号増幅器１ｍの利得をβ［ｄＢ］、ハイブリッド回路１ｋの逆結合減衰量を−Ａ［ｄＢ］とすると、送信信号受信部１ｃが受信する信号のレベルは、信号送信部１ｂが送信した信号のレベルと同じ（０［ｄＢ］）であるが、伝送信号受信部１ｄが受信する信号のレベルは、信号送信部１ｂが送信した信号のレベルに対して利得が−ｒ＋α−Ａ＋β［ｄＢ］となっているため、送信信号受信部１ｃと伝送信号受信部１ｄとで受信する信号のレベルを同一にするためには、−ｒ＋α−Ａ＋β＝０、つまりα＋β＝Ａ＋ｒでなければならない。
【００５６】
則ち、送信信号受信部１ｃと伝送信号受信部１ｄとが受信する信号のレベルを同一にして信号衝突検出部１ｅの衝突検出機能を正常に働かせるためには、送信信号増幅器１ｌと受信信号増幅器１ｍとは、合わせて、ハイブリッド回路１ｋにおける逆結合減衰量分と抵抗Ｒにおける減衰量分だけ信号を増幅させればよい。
【００５７】
尚、抵抗Ｒが無ければ、送信信号増幅器１ｌと受信信号増幅器１ｍとはハイブリッド回路１ｋにおける逆結合減衰量分だけ信号を増幅させればよい。
【００５８】
また、受信信号増幅器１ｍと伝送信号受信部１ｄとの間にアッテネータ（減衰量：−Ｂ［ｄＢ］）を挿入すれば、伝送信号受信部１ｄが受信するデータ信号のレベルは、信号送信部１ｂが送信したデータ信号のレベルに対して利得が−ｒ＋α−Ａ＋β−Ｂ［ｄＢ］となり、α＋β＝ｒ＋Ａ＋Ｂが成り立つように、信号を増幅させればよい。
【００５９】
かかる通信システムにおいては、通信端末は信号衝突検出機能を失わずにデータ信号を増幅して送信することが可能となり、通信システム全体の伝送距離および分岐接続数の両最大値を増加することができる。また、ハイブリッド回路が２線４線変換回路の役割も兼ねることができるので、２線４線変換回路が不要となる。また、実施形態２と比較するとハイブリッド回路が１つで済み、分岐器へＤＣ電源を送信するためのＤＣ電源重畳部、ＤＣ電源とデータ信号とを分離させる電源分離回路も不要となるため、低コスト化を図ることができる。
【００６０】
（実施形態４）
本実施形態における通信システムの基本構成は実施形態３と共通するために共通する部分については同一の符号を付して説明を省略し、本実施形態の特徴となる部分についてのみ詳細に説明する。
【００６１】
本実施形態の通信システムは、実施形態３の通信端末１Ｂに代えて、図８に示した通信端末１Ｃを備えた点に特徴がある。
【００６２】
この通信端末１Ｃは、信号送信部１ｂと、送信信号受信部１ｃと、伝送信号受信部１ｄと、信号衝突検出部１ｅと、ＣＰＵ１ｆと、電源部１ｇと、内部電源１ｈと、端子部１ｉと、ハイブリッド回路１ｋと、送信信号増幅器１ｌとを実施形態３の通信端末１Ｂと同様に備えおり、通信端末１Ｂとの相違点として、受信信号増幅器１ｍを省いて、ハイブリッド回路１ｋの第３の入出力端子１２と伝送信号受信部１ｄとを直接接続した構成となっている。
【００６３】
ただし、本実施形態の送信信号増幅器１ｌの利得は、後述するように、実施形態３の送信信号増幅器１ｌの利得とは異なっている。
【００６４】
実施形態３で述べたように、通信端末の信号衝突検出部１ｅが正常に機能するには、送信信号受信部１ｃと伝送信号受信部１ｄとが受信する信号のレベルが同一である必要があった。よって、本実施形態の通信端末１Ｃでは、送信信号増幅器１ｌのみで、送信する信号をハイブリッド回路１ｋの逆結合減衰量分と抵抗Ｒにおける減衰量分だけ増幅させ、受信する信号は増幅せずに通過させる構成とし、送信信号受信部１ｃと伝送信号受信部１ｄとが受信する信号のレベルを同一に保って信号の衝突検出機能を働かせている。
【００６５】
かかる通信システムにおいては、通信端末は、信号衝突検出機能を失わずに、実施形態３で双方向の増幅器で実現していた利得を１台の送信方向の増幅器で実現したため、送信時に予めノイズに対してレベルの大きいデータ信号を送信することが可能となり、信号対ノイズ比（Ｓ／Ｎ比）が向上し、信頼性の高い高品位のシステムを実現することが可能となる。また、増幅器の数も削減できるため、さらなる低コスト化を図ることができる。
【００６６】
【発明の効果】
請求項１の発明は、複数の通信端末と、これらの各通信端末に接続される分岐器と、これらの各分岐器間に接続される平衡２線ケーブルとにより構成され、前記複数の通信端末が前記分岐器および前記平衡２線ケーブルを介して相互にデータ信号を送受信する通信システムであって、前記通信端末は、送信するべきデータ信号から被変調波信号を生成し前記平衡２線ケーブルに送信する信号送信部と、その信号送信部が送信した自らの被変調波信号を受信しこれを復調してデータ信号を得る送信信号受信部と、前記平衡２線ケーブルからの被変調波信号を受信しこれを復調してデータ信号を得る伝送信号受信部と、前記送信信号受信部と前記伝送信号受信部とが受信し復調して得られた夫々のデータ信号を比較することにより前記平衡２線ケーブル上のデータ信号の衝突を検出する信号衝突検出部とを備え、前記分岐器は、前記平衡２線ケーブルと接続するための一対の送り端子部と、当該分岐器を前記通信端末に接続するための分岐端子部と、分岐回路部を含み、前記分岐回路部は、前記一対の送り端子部間の両ラインと前記分岐端子部との間に介設され前記平衡２線ケーブルに対してハイインピーダンスとなる一対の抵抗と、これら一対の抵抗と前記分岐端子部との間に介設され前記平衡２線ケーブルとインピーダンス整合をとるためのトランスとにより構成されるので、分岐回路部により高インピーダンスで被変調波信号の分岐を行うことで、分岐点における挿入損失を低減することができ、またトランスを用いて分岐箇所での平衡２線ケーブルと分岐器とのインピーダンス整合を保つことで、平衡２線ケーブル上における被変調波信号の減衰を低減することができるので、被変調波信号の減衰ないしは反射の影響が減少され、衝突検出機能を有した通信システムにおいて、伝送距離および分岐接続数の両最大値を増加することができるという効果がある。
【００６７】
請求項２の発明は、請求項１記載の発明において、前記分岐器は、前記送り端子部からの被変調波信号を増幅する受信信号増幅器と、前記分岐端子部からの被変調波信号を増幅する送信信号増幅器と、第１の入出力端子から入力された被変調波信号を分配して第２，第３の入出力端子から出力し、第２，第３の入出力端子から入力された被変調波信号を混合して前記第１の入出力端子から出力する２つのハイブリッド回路とを有し、一方の前記ハイブリッド回路の第１の入出力端子を前記分岐回路部と前記分岐端子部との間で前記分岐回路部側に接続し、他方のハイブリッド回路の第１の入出力端子を前記分岐回路部と前記分岐端子部との間で前記分岐端子部側に接続し、２つの前記ハイブリッド回路の第２，第３の入出力端子間を、前記受信信号増幅器と前記送信信号増幅器とで接続したので、分岐器内でデータ信号の双方向増幅が可能となり、請求項１の発明よりさらに伝送距離および分岐接続数の両最大値を増加することができるという効果がある。
【００６８】
請求項３の発明は、請求項１記載の発明において、前記通信端末は、第１の入出力端子から入力された被変調波信号を分配して第２，第３の入出力端子から出力し第２，第３の入出力端子から入力された被変調波信号を混合して前記第１の入出力端子から出力するハイブリッド回路を有し、前記ハイブリッド回路の第１の入出力端子を前記平衡２線ケーブルと接続し、前記ハイブリッド回路の第２の入出力端子と前記信号送信部との間に、前記信号送信部からの被変調波信号を増幅する送信信号増幅器を接続し、前記ハイブリッド回路の第３の入出力端子と前記伝送信号受信部との間に、前記平衡２線ケーブルからの被変調波信号を増幅する受信信号増幅器を接続して構成され、前記送信信号増幅器と前記受信信号増幅器は、合わせて、前記ハイブリッド回路における逆結合減衰量分だけ被変調波信号を増幅させるので、通信端末は信号衝突検出機能を失わずにデータ信号を増幅して送信することが可能となり、衝突検出機能を有した通信システム全体の伝送距離および分岐接続数の両最大値を増加することができるという効果がある。
【００６９】
請求項４の発明は、請求項１記載の発明において、前記通信端末は、第１の入出力端子から入力された被変調波信号を分配して第２，第３の入出力端子から出力し第２，第３の入出力端子から入力された被変調波信号を混合して前記第１の入出力端子から出力するハイブリッド回路を有し、前記ハイブリッド回路の第１の入出力端子を前記平衡２線ケーブルと接続し、前記ハイブリッド回路の第２の入出力端子と前記信号送信部との間に、前記信号送信部からの被変調波信号を増幅する送信信号増幅器を接続し、前記ハイブリッド回路の第３の入出力端子と前記伝送信号受信部とを接続して構成され、前記送信信号増幅器は、前記ハイブリッド回路における逆結合減衰量分だけ被変調波信号を増幅させるので、信号衝突検出機能を失わずに、送信時に予めノイズに対してレベルの大きいデータ信号を送信でき、信号対ノイズ比（Ｓ／Ｎ比）を向上できるので、より信頼性の高い高品位の通信システムを実現することが可能となり、さらにデータ信号を増幅させる増幅器の台数も削減できるため、低コスト化も図ることができるという効果がある。
【図面の簡単な説明】
【図１】実施形態１の通信システムのシステム構成を示すブロック図である。
【図２】同上の通信端末の構成を示すブロック図である。
【図３】同上の分岐器の構成を示すブロック図である。
【図４】実施形態２の通信システムの通信端末の構成を示すブロック図である。
【図５】同上の分岐器の構成を示すブロック図である。
【図６】同上の要部を説明する説明図である。
【図７】実施形態３の通信システムの通信端末の構成を示すブロック図である。
【図８】実施形態４の通信システムの通信端末の構成を示すブロック図である。
【図９】従来の通信システムのシステム構成を示すブロック図である。
【符号の説明】
１　通信端末
１ａ　２線４線変換回路
１ｂ　信号送信部
１ｃ　送信信号受信部
１ｄ　伝送信号受信部
１ｅ　信号衝突検出部
１ｆ　ＣＰＵ部
１ｇ　電源部
１ｈ　内部電源
１ｉ　端子部
１ｊ　ＤＣ電源重畳部
１ｋ　ハイブリッド回路
１ｌ　送信信号増幅器
１ｍ　受信信号増幅器
２　分岐器
２ａ，２ｂ　送り端子部
２ｃ　分岐端子部
２ｄ　分岐回路部
２ｅ，２ｆ　ハイブリッド回路
２ｇ　受信信号増幅器
２ｈ　送信信号増幅器
２ｉ　ＤＣ電源分離部
２ｊ　内部電源
Ｃ１，Ｃ２　平衡２線ケーブル
Ｚ　終端部材[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a communication system for transmitting and receiving data signals.
[0002]
[Prior art]
FIG. 9 is a diagram showing a configuration example of a conventional general communication system. The communication system shown in FIG. 1 includes a plurality of communication terminals 100 and a balanced two-wire cable (pair wire) C branched and connected to each of the communication terminals 100. Data signals are mutually transmitted and received via C.
[0003]
The communication terminal 100 includes a terminal unit 100i for connecting the communication terminal 100 to another communication terminal 100 via a balanced two-wire cable C, a CPU unit 100f for executing various processes such as transmission and reception of a data signal, and A signal transmitting section 100b for generating a modulated wave signal from a data signal to be transmitted from the CPU section 100f and transmitting the modulated signal from the terminal section 100i to another communication terminal 100, and a modulated signal transmitted by the signal transmitting section 100b. And a modulated signal from the balanced two-wire cable C coming into the terminal unit 100i. The transmission signal receiving unit 100c receives a wave signal and outputs a data signal obtained by demodulating the signal to the signal collision detection unit 100e. A transmission signal receiving unit 100d that receives and demodulates the data signal and outputs the data signal to the CPU unit 100f and the signal collision detection unit 100e; A signal collision detection unit that detects a collision of data signals on the balanced two-wire cable C by comparing respective data signals obtained by the transmission unit 100c and the transmission signal reception unit 100d, and a signal transmission unit 100b , A two-wire / four-wire conversion circuit 100a interposed between the input of the output and transmission signal receiving part 100d and the terminal part 100i, a power supply part 100g for converting AC power of an AC power supply into DC power, And an internal power supply 100h that generates driving power from the DC power converted by 100g and supplies the driving power to each unit.
[0004]
In such a communication system, the modulated signal is generated from the data signal and the carrier signal by the signal transmission unit 100b of the communication terminal 100, and transmitted onto the balanced two-wire cable C via the two-wire / four-wire conversion circuit 100a. You. The transmitted modulated wave signal is received by another communication terminal 100, demodulated by the transmission signal receiving unit 100d, and decoded into the original data signal.
[0005]
Here, as for the frequency of the transmission signal on the balanced two-wire cable C, the same frequency band is used for the uplink and the downlink. The wiring form is a multi-drop which can be branched at any point, and the balanced two-wire cables C are directly connected at the branch point.
[0006]
In the case of such a communication method, if a plurality of communication terminals 100 transmit simultaneously, the signals transmitted to the balanced two-wire cable C collide, and any of the communication terminals 100 may normally receive the signal of the communication partner. become unable. Therefore, in general, each communication terminal 100 monitors the data signal received by the transmission signal receiving unit 100d before transmission to determine whether there is a signal being transmitted on the balanced two-wire cable C. Is to be detected. Then, when it is detected that there is a signal being transmitted on the balanced two-wire cable C, the transmission timing is postponed, the detection is performed again, and if there is no signal being transmitted, the transmission timing is adjusted so that transmission is performed. Is to be performed.
[0007]
In addition, during transmission of the modulated wave signal, the communication device 100 determines whether the data signal is normally transmitted by the signal collision detection unit 100e or collides with a data signal transmitted from another communication device 100. Has been detected. That is, when the data signals of the transmission signal receiving unit 100d and the transmission signal receiving unit 100c match, it is determined that the number of signals transmitted on the balanced two-wire cable C is one and no signal collision occurs. If they do not match, there are a plurality of signals transmitted on the balanced two-wire cable C, and it is determined that a signal collision has occurred. When the collision of the data signal is detected, the modulated wave signal being transmitted is stopped, and transmission of the modulated wave signal is tried again after a while.
[0008]
[Problems to be solved by the invention]
However, in the above-described conventional communication system, although transmission and reception of signals can be suitably performed while avoiding collision of signals, at the branch point x of the balanced two-wire cable C, the cables are directly connected to each other. At the branch point x, the impedance of the balanced two-wire cable decreases, and there is a problem that the modulated wave signal, which is the transmission signal, is attenuated and reflected. Also, when the amplitude of the modulated wave signal becomes small and the modulated wave signal has large distortion, demodulation of the data signal becomes impossible, and both the maximum value of the transmission distance and the number of branch connections increase. I can't.
[0009]
The present invention has been made in view of the above problems, and an object of the present invention is to increase both the maximum value of the transmission distance and the number of branch connections in a communication system having a collision detection function. A communication system is provided.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a plurality of communication terminals, a branch unit connected to each of these communication terminals, and a balanced two-wire cable connected between these branch units. A communication system, wherein the plurality of communication terminals mutually transmit and receive data signals via the branching device and the balanced two-wire cable, wherein the communication terminal converts a modulated wave signal from a data signal to be transmitted. A signal transmitting unit that generates and transmits the signal to the balanced two-wire cable, a transmission signal receiving unit that receives the own modulated wave signal transmitted by the signal transmitting unit, demodulates the signal, and obtains a data signal; A transmission signal receiving unit that receives a modulated wave signal from a cable and demodulates the signal to obtain a data signal; and a data signal obtained by receiving and demodulating the transmission signal receiving unit and the transmission signal receiving unit. Compare A signal collision detection unit for detecting a collision of a data signal on the balanced two-wire cable, wherein the branch unit includes a pair of feed terminal units for connecting to the balanced two-wire cable, and the branch unit. A branch terminal unit for connecting to the communication terminal; and a branch circuit unit, wherein the branch circuit unit is interposed between both lines between the pair of feed terminal units and the branch terminal unit, and is connected to the balanced terminal. A pair of resistors having a high impedance with respect to the line cable, and a transformer interposed between the pair of resistors and the branch terminal for impedance matching with the balanced two-wire cable. did.
[0011]
According to a second aspect of the present invention, in the first aspect of the present invention, the branching unit amplifies a modulated wave signal from the branch terminal unit with a reception signal amplifier for amplifying a modulated wave signal from the sending terminal unit. And the modulated signal input from the first input / output terminal is distributed and output from the second and third input / output terminals, and input from the second and third input / output terminals. And two hybrid circuits for mixing the modulated wave signal and outputting the mixed wave signal from the first input / output terminal, wherein the first input / output terminal of one of the hybrid circuits is connected to the branch circuit unit and the branch terminal unit. And the first input / output terminal of the other hybrid circuit is connected to the branch terminal portion between the branch circuit portion and the branch terminal portion, and the two hybrid circuits are connected to each other. Between the second and third input / output terminals of the circuit. It was obtained by connecting between the signal amplifier and the transmission signal amplifier.
[0012]
According to a third aspect of the present invention, in the first aspect, the communication terminal distributes the modulated wave signal input from the first input / output terminal and outputs the modulated wave signal from the second and third input / output terminals. A hybrid circuit that mixes the modulated wave signals input from the second and third input / output terminals and outputs the mixed signal from the first input / output terminal; A transmission signal amplifier for amplifying a modulated wave signal from the signal transmission unit between a second input / output terminal of the hybrid circuit and the signal transmission unit; A reception signal amplifier for amplifying a modulated wave signal from the balanced two-wire cable is connected between the third input / output terminal of the transmission signal reception section and the transmission signal reception section. The amplifier, together, Only antijoin attenuation amount in hybrid circuit was assumed to amplify the modulated wave signal.
[0013]
According to a fourth aspect of the present invention, in the first aspect, the communication terminal distributes the modulated wave signal input from the first input / output terminal and outputs the modulated wave signal from the second and third input / output terminals. A hybrid circuit that mixes the modulated wave signals input from the second and third input / output terminals and outputs the mixed signal from the first input / output terminal; A transmission signal amplifier for amplifying a modulated wave signal from the signal transmission unit between a second input / output terminal of the hybrid circuit and the signal transmission unit; The third input / output terminal is connected to the transmission signal receiving section, and the transmission signal amplifier amplifies the modulated wave signal by an amount of reverse coupling attenuation in the hybrid circuit.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to Embodiments 1 to 4.
(Embodiment 1)
FIG. 1 is a diagram illustrating a configuration example of a communication system according to a first embodiment of the present invention, FIG. 2 is a configuration diagram of a communication terminal in the communication system, and FIG. 3 is a configuration diagram of a branching device in the communication system.
[0015]
As shown in FIG. 1, the communication system according to the first embodiment includes a plurality of communication terminals 1, a branch unit 2 connected to each of the communication terminals 1, and a balance connected between each of the branch units 2. A plurality of communication terminals 1 are configured to transmit and receive data signals to and from each other via the splitter 2 and the balanced two-wire cable C1.
[0016]
As shown in FIG. 2, the communication terminal 1 includes a terminal unit 1i connected to a branch unit 2 (connected to the communication terminal 1) immediately below via a balanced two-wire cable C2, and transmission and reception of data signals. And a signal for generating a modulated wave signal from the data signal to be transmitted from the CPU unit 1f and transmitting the modulated wave signal to another communication terminal 1 via the branch unit 2 immediately below. A transmitting unit 1b, a transmitting signal receiving unit 1c that receives its own modulated wave signal transmitted by the signal transmitting unit 1b, and outputs a data signal obtained by demodulating the signal to a signal collision detecting unit 1e; A transmission signal receiving unit 1d for receiving a modulated wave signal from the balanced two-wire cables C1 and C2 coming into the CPU and outputting a data signal obtained by demodulating the modulated signal to the CPU unit 1f and the signal collision detection unit 1e; Transmission signal receiving unit 1c A signal collision detector 1e for detecting a collision of data signals on the balanced two-wire cables C1 and C2 by comparing respective data signals received and demodulated by the transmission signal receiver 1d, and a signal transmitter 1b, a two-wire / four-wire conversion circuit 1a interposed between the input of the transmission signal receiving part 1d and the terminal part 1i, a power supply part 1g for converting the AC power of the AC power supply into the DC power, An internal power supply 1h that generates drive power from the DC power converted by the unit 1g and supplies the drive power to each unit.
[0017]
As shown in FIG. 3, the branching device 2 connects the branching device 2 to the communication terminal 1 via a pair of feed terminals 2a and 2b for connecting to the balanced two-wire cable C1, and the balanced two-wire cable C2. And a branch circuit section 2d.
[0018]
The terminals 20 and 21 of the sending terminal 2a and the terminals 22 and 23 of the sending terminal 2b are electrically connected to each other inside the branching device 2.
[0019]
The branch circuit unit 2d has less attenuation of the modulated wave signal transmitted from one of the pair of feed terminal units 2a and 2b than the modulated wave signal transmitted from the other send terminal unit. Thus, the branch points are connected with high impedance, and the impedance of the branch terminal 2c is configured to be equal to the characteristic impedance of the transmission line of the modulated wave signal. That is, a pair of resistors R1 and R2, which are interposed between the two lines LN1 and LN2 between the pair of sending terminal portions 2a and 2b and the branch terminal portion 2c and have a high impedance with respect to the balanced two-wire cable C1, A pair of capacitors C1 and C2 provided in series between the resistors R1 and R2 and the two lines LN1 and LN2, and a pair of capacitors C1 and C2 provided between the pair of resistors R1 and R2 and the branch terminal 2c. It comprises a transformer T1 for impedance matching with the line cable C2, and a pair of capacitors C3 and C4 provided between the transformer T1 and the branch terminal 2c.
[0020]
Capacitors C1, C2, C3, and C4 are provided to block the passage of low frequency components. The resistors R1 and R2 have an impedance value sufficiently larger than the characteristic impedance of the balanced two-wire cable C1, and branch the modulated wave signal without affecting the characteristic impedance of the balanced two-wire cable C1 at the branch point. It plays a role of transmitting to the terminal portion 2c. The turns ratio of the transformer T1 is adjusted so that the characteristic impedance seen from the branch terminal 2c side is equal to the characteristic impedance of the balanced two-wire cable C1. In addition, a terminal member Z composed of a capacitor and a resistor is connected to one of the feed terminals of the branching device 2 serving as a terminal.
[0021]
In the communication system configured as described above, a modulated wave signal is generated from a data signal and a carrier wave signal by the signal transmission unit 1b of the communication terminal 1 and is transmitted via the two-wire / four-wire conversion circuit 1a and the balanced two-wire cable C2. The signal is transmitted to the branch terminal 2c of the branching device 2. The transmitted modulated wave signal is transmitted to a pair of sending terminal units 2a and 2b via a branch circuit unit 2d, and is transmitted from the transmission terminal units 2a and 2b to respective balanced two-wire cables C1. Transmitted to
[0022]
In each of the two splitters 2, the modulated wave signal that has entered one sending terminal is transmitted from the other sending terminal to another splitter 2. In this way, the modulated wave signal is transmitted to all the other splitters 2.
[0023]
In each of these branching devices 2, the modulated wave signal that has entered one of the sending terminal portions is transmitted to the branching terminal portion 2c via the branching circuit portion 2d, and transmitted therefrom onto the balanced two-wire cable C2. Then, it is sent to another communication terminal 1.
[0024]
In another communication terminal 1, the modulated wave signal is demodulated by the transmission signal receiving unit 1d and decoded into the original data signal.
[0025]
In short, in each splitter 2, the modulated wave signal that has entered the branch terminal portion 2c is output from each of the pair of sending terminal portions 2a and 2b, and the modulated wave signal that has entered one sending terminal portion is the other. The modulated wave signal output from the sending terminal portion and the branch terminal portion 2c and entering the other sending terminal portion is output from the one sending terminal portion and the branch terminal portion 2c.
[0026]
According to such a communication system, since the impedance matching of the balanced two-wire cable C1 is maintained in the splitter 2, and the modulated wave signal is branched with high impedance, the insertion loss at the branch point of the modulated wave signal is reduced. Therefore, both the maximum values of the transmission distance and the number of branch connections can be increased.
[0027]
(Embodiment 2)
The basic configuration of the communication system according to the present embodiment is the same as that of the first embodiment, and the same reference numerals are given to parts common to the first embodiment, and description thereof is omitted. This will be described in detail.
[0028]
The communication system according to the present embodiment includes a communication terminal 1A and a branch unit 2A shown in FIGS. 4 and 5, respectively, instead of the communication terminal 1 and the branch unit 2, as compared with the communication system according to the first embodiment. There is a characteristic in the point.
[0029]
As shown in FIG. 4, the communication terminal 1A includes a two-wire / four-wire conversion circuit 1a, a signal transmission unit 1b, a transmission signal reception unit 1c, a transmission signal reception unit 1d, a signal collision detection unit 1e, and a CPU 1f. , A power supply unit 1g, an internal power supply 1h, and a terminal unit 1i in the same manner as the communication terminal 1 of the first embodiment, and a difference from the communication terminal 1 is a DC power supply superimposition unit 1j. .
[0030]
The DC power supply superimposing unit 1j is interposed between the two-wire / four-wire conversion circuit 1a and the terminal unit 1i, obtains DC power from the power supply unit 1g, and secures DC power for the branch unit 2A immediately below. The DC power is output from the terminal 1i.
[0031]
As shown in FIG. 5, the branching device 2A includes feed terminals 2a and 2b, a branch terminal 2c, and a branch circuit 2d in the same manner as the branching device 2 of the first embodiment. As a difference from the first embodiment, a first hybrid circuit 2e, a second hybrid circuit 2f, a reception signal amplifier 2g, a transmission signal amplifier 2h, a DC power supply separation unit 2i, and an internal power supply 2j are provided.
[0032]
The first and second hybrid circuits 2e and 2f distribute the modulated wave signals input from the respective first input / output terminal units 24 and 27 to each of the second input / output terminal units 25 and 28 and The signals are output from the third input / output terminals 26 and 29, and the modulated wave signals input from the second and third input / output terminals are mixed to form the first input / output terminals 24. , 27. The first input / output terminal section 24 of the first hybrid circuit 2e is connected to the branch circuit section 2d between the branch circuit section 2d and the branch terminal section 2c, and the first input / output terminal section 24 of the second hybrid circuit 2f. The output terminal 27 is connected to the branch terminal 2c between the branch circuit 2d and the branch terminal 2c. A transmission signal amplifier 2h is connected between the second input / output terminals 25 and 28 of each hybrid circuit, and a reception signal amplifier 2g is connected between the third input / output terminals 26 and 29.
[0033]
The transmission signal amplifier 2h is for amplifying the modulated wave signal from the branch terminal 2c, and the reception signal amplifier 2g is for amplifying the modulated wave signal from the transmission terminals 2a and 2b. is there.
[0034]
The DC power separation section 2i is connected between the second hybrid circuit 2f and the branch terminal section 2c, separates the modulated wave signal and the DC power from the communication terminal 1A from each other, and separates the modulated wave signal into the second signal. , While supplying DC power to the internal power supply 2j.
[0035]
The internal power supply 2j supplies necessary power to each section of the branching device 2A by using DC power supplied from the DC power supply separation section 2i.
[0036]
Here, the first and second hybrid circuits will be described in more detail with reference to FIG. The first hybrid circuit 2e includes transformers T2 to T5 and resistors R3 and R4. Transformers T2 and T3 connected in parallel are connected to respective terminals of the first input / output terminal unit 24. One terminal of the second input / output terminal 25 is connected to one end of the transformer T4 and one end of the resistor R3, and the other terminal of the second input / output terminal 25 is connected to one end of the transformer T5 and one end of the resistor R4. I have. One terminal of the third input / output terminal 26 is connected to the other end of the transformer T4 and the resistor R3, and the other terminal of the third input / output terminal 26 is connected to the other end of the transformer T5 and the resistor R4. ing.
[0037]
Similarly, the second hybrid circuit 2f also includes transformers T6 to T9 and resistors R5 and R6, and each terminal of the first input / output terminal 27 is connected to the transformers T8 and T9 coupled in parallel. Of the transformer T6 and one end of the resistor R5, the other terminal of the second input / output terminal 28 is connected to one end of the transformer T7 and the resistor R6, and the third input / output terminal 29 Is connected to the other end of the transformer T7 and the resistor R6, and the other terminal of the third input / output terminal unit 29 is connected to the other end of the transformer T6 and the resistor R5.
[0038]
Here, the resistors R3 to R6 are resistors for determining the output impedance on the amplifier connection side, and also absorb the unbalanced power. The transformers T4 to T7 play a role of distributing a signal into two or mixing two signals into one. Transformers T2 and T3 are used for impedance matching of the first input / output terminal unit 24 of the first hybrid circuit 2e, and transformers T8 and T9 are used for impedance matching of the first input / output terminal unit 27 of the second hybrid circuit 2f. In this case, the turn ratio is adjusted to achieve matching.
[0039]
In the hybrid circuit configured as described above, the modulated wave signal input from the first input / output terminal unit 24 of the first hybrid circuit 2e is equally divided into two signal components, and the second input / output The signal is output to the terminal 25 and the third input / output terminal 26.
[0040]
The signal component output to the third input / output terminal 26 is amplified by the gain of the reception signal amplifier 2g connected in the forward direction, and input to the third input / output terminal 29 of the second hybrid circuit 2f. You.
[0041]
On the other hand, since the transmission signal amplifier 2h connected in the reverse direction is connected to the second input / output terminal unit 25, the signal component output from the second input / output terminal unit 25 There is no transmission to the second input / output terminal section 28 of the circuit 2f.
[0042]
The modulated wave signal input to the third input / output terminal unit 29 of the second hybrid circuit 2f passes again through the second hybrid circuit 2f to the first input / output terminal 27 of the second hybrid circuit 2f. Output from
[0043]
At this time, since there is a reverse coupling attenuation between the third input / output terminal unit 29 and the second input / output terminal unit 28 of the second hybrid circuit 2f, the third input / output terminal unit 29 The amount of the signal component input to the second input / output terminal unit 28 leaking to the second input / output terminal unit 28 is extremely small. However, in order to prevent signal oscillation, when the reverse coupling attenuation per hybrid circuit is -A [dB], the total gain of the reception signal amplifier 2g and the transmission signal amplifier 2h must not exceed 2A [dB]. No.
[0044]
Similarly, the modulated wave signal input from the first input / output terminal unit 27 of the second hybrid circuit 2f is distributed by the second hybrid circuit 2f and output from the second input / output terminal unit 28. After the component is amplified by the gain of the transmission signal amplifier 2h, it is output from the first input / output terminal 24 of the first hybrid circuit 2e.
[0045]
In such a communication system, the modulated wave signal can be bidirectionally amplified in the splitter 2A, and the modulated wave signal transmitted from the communication terminal 1A can be transmitted to another communication terminal 1A at an appropriate level. At the same time, a modulated wave signal from another communication terminal 1A can be received at an appropriate level, and both the maximum transmission distance and the maximum number of branch connections of the entire communication system can be further increased compared to the first embodiment.
[0046]
(Embodiment 3)
The basic configuration of the communication system according to the present embodiment is the same as that of the first embodiment or the second embodiment. Only will be described in detail.
[0047]
The communication system of the present embodiment is characterized in that a communication terminal 1B shown in FIG. 7 is provided instead of the communication terminal 1 of the first embodiment. The configuration of the branching device 2 is the same as that of the first embodiment.
[0048]
The communication terminal 1B includes a signal transmission unit 1b, a transmission signal reception unit 1c, a transmission signal reception unit 1d, a signal collision detection unit 1e, a CPU 1f, a power supply unit 1g, an internal power supply 1h, and a terminal unit 1i. In addition to being provided in the same manner as the communication terminal 1 of the first embodiment, the difference from the communication terminal 1 is that the two-wire / four-wire conversion circuit 1a is omitted, the hybrid circuit 1k, the transmission signal amplifier 11l, and the reception signal amplifier 1m And
[0049]
The hybrid circuit 1k, the transmission signal amplifier 11 and the reception signal amplifier 1m are the same as the hybrid circuit 2e, the transmission signal amplifier 2h and the reception signal amplifier 2g of the second embodiment, respectively. The second hybrid circuit 2e, the transmission signal amplifier 2h, and the reception signal amplifier 2g are equivalent to those obtained by moving from the inside of the branching unit to the inside of the communication terminal.
[0050]
The first input / output terminal 10 of the hybrid circuit 1k is connected to the terminal 1i, the second input / output terminal 11 is connected to the output end of the transmission signal amplifier 11 and the third input / output terminal 12 Is connected to the input terminal of the reception signal amplifier 1m.
[0051]
The input end of the transmission signal amplifier 11 is connected to the signal transmission unit 1b via the resistor R, and amplifies the modulated wave signal from the signal transmission unit 1b. The output end of the reception signal amplifier 1m is connected to the transmission signal reception unit 1d, amplifies the modulated wave signal that has entered the terminal unit 1i, and inputs the amplified signal to the transmission signal reception unit 1d.
[0052]
In the communication system configured as described above, the modulated wave signal transmitted from the signal transmission unit 1b is amplified by the transmission signal amplifier 11 and is transmitted from the terminal unit 1i to the balanced two-wire cable C2 via the hybrid circuit 1k. Sent.
[0053]
The modulated wave signal that has entered the terminal unit 1i from the balanced two-wire cable C2 is equally divided into two signal components by the hybrid circuit 1k, and is output from the second and third input / output terminal units 11 and 12. Is done. The signal component output from the third input / output terminal unit 12 is amplified by the reception signal amplifier 1m connected in the forward direction, and then input to the transmission signal reception unit 1d. On the other hand, since the transmission signal amplifier 11 connected in the opposite direction is connected to the second input / output terminal unit 11, the signal component output from the second input / output terminal unit 11 is transmitted to the signal transmission unit 1b. I will not.
[0054]
Here, the gains of the transmission signal amplifier 11 and the reception signal amplifier 1m will be described. The signal collision detection unit 1e compares a signal received by the transmission signal reception unit 1d during transmission of the data signal with a signal transmitted by the transmission signal reception unit 1c and transmits a balanced two-wire signal if they match. It is determined that there is only one signal transmitted on the cable C and no signal collision has occurred. If they do not match, there are a plurality of signals transmitted on the balanced two-wire cable C, and the signal collision occurs. Judge that is happening. Therefore, in order for the collision detection function to operate normally, the signal levels received by the transmission signal receiving unit 1c and the transmission signal receiving unit 1d need to be the same.
[0055]
Here, the amount of attenuation at the resistor R provided between the signal transmission unit 1b and the transmission signal amplifier 11 is -r [dB], the gain of the transmission signal amplifier 11 is α [dB], and the gain of the reception signal amplifier 1m is Is β [dB] and the reverse coupling attenuation of the hybrid circuit 1 k is −A [dB], the level of the signal received by the transmission signal receiving unit 1 c is the same as the level of the signal transmitted by the signal transmitting unit 1 b (0 [DB]), but the level of the signal received by the transmission signal receiving unit 1d is -r + α-A + β [dB] with respect to the level of the signal transmitted by the signal transmitting unit 1b. In order to make the levels of the signals received by the signal receiving unit 1c and the transmission signal receiving unit 1d the same, -r + α-A + β = 0, that is, α + β = A + r.
[0056]
That is, in order for the level of signals received by the transmission signal receiving unit 1c and the transmission signal receiving unit 1d to be the same and the collision detection function of the signal collision detection unit 1e to operate normally, the transmission signal amplifier 11 and the reception signal amplifier 11 In addition, the signal may be amplified by the amount corresponding to the amount of reverse coupling attenuation in the hybrid circuit 1k and the amount of attenuation in the resistor R together with 1m.
[0057]
If the resistor R is not provided, the transmission signal amplifier 11 and the reception signal amplifier 1m need only amplify the signal by the amount of reverse coupling attenuation in the hybrid circuit 1k.
[0058]
Also, if an attenuator (attenuation: -B [dB]) is inserted between the reception signal amplifier 1m and the transmission signal receiving unit 1d, the level of the data signal received by the transmission signal receiving unit 1d can be changed to the level of the signal transmitting unit 1b. It is sufficient to amplify the signal so that the gain becomes -r + [alpha] -A + [beta] -B [dB] with respect to the level of the transmitted data signal, and [alpha] + [beta] = r + A + B.
[0059]
In such a communication system, the communication terminal can amplify and transmit a data signal without losing the signal collision detection function, and can increase both the maximum transmission distance and the maximum number of branch connections of the entire communication system. . Further, since the hybrid circuit can also serve as a two-wire / four-wire conversion circuit, a two-wire / four-wire conversion circuit is not required. Further, as compared with the second embodiment, only one hybrid circuit is required, and a DC power supply superimposing unit for transmitting DC power to the branching unit and a power supply separation circuit for separating the DC power supply from the data signal are not required. Cost can be reduced.
[0060]
(Embodiment 4)
Since the basic configuration of the communication system according to the present embodiment is common to that of the third embodiment, the same reference numerals are given to the common parts, and the description thereof will be omitted. Only the features that are the features of the present embodiment will be described in detail.
[0061]
The communication system of the present embodiment is characterized in that a communication terminal 1C shown in FIG. 8 is provided instead of the communication terminal 1B of the third embodiment.
[0062]
The communication terminal 1C includes a signal transmission unit 1b, a transmission signal reception unit 1c, a transmission signal reception unit 1d, a signal collision detection unit 1e, a CPU 1f, a power supply unit 1g, an internal power supply 1h, a terminal unit 1i, , The hybrid circuit 1k and the transmission signal amplifier 11 are provided in the same manner as the communication terminal 1B of the third embodiment. The difference from the communication terminal 1B is that the reception signal amplifier 1m is omitted and the third input of the hybrid circuit 1k is omitted. In this configuration, the output terminal 12 and the transmission signal receiving unit 1d are directly connected.
[0063]
However, the gain of the transmission signal amplifier 11 of the present embodiment is different from the gain of the transmission signal amplifier 11 of the third embodiment, as described later.
[0064]
As described in the third embodiment, in order for the signal collision detection unit 1e of the communication terminal to function properly, the levels of the signals received by the transmission signal reception unit 1c and the transmission signal reception unit 1d need to be the same. Was. Therefore, in the communication terminal 1C of the present embodiment, the transmission signal is amplified only by the transmission signal amplifier 11 and the reverse coupling attenuation of the hybrid circuit 1k and the attenuation of the resistor R, and the received signal is not amplified. The transmission signal receiving section 1c and the transmission signal receiving section 1d operate at the same signal level while maintaining the same level of the signals received.
[0065]
In such a communication system, the communication terminal realizes the gain realized by the two-way amplifier in the third embodiment with one amplifier in the transmission direction without losing the signal collision detection function. On the other hand, a data signal having a higher level can be transmitted, the signal-to-noise ratio (S / N ratio) is improved, and a highly reliable, high-quality system can be realized. Further, since the number of amplifiers can be reduced, the cost can be further reduced.
[0066]
【The invention's effect】
The invention according to claim 1 comprises a plurality of communication terminals, a branch unit connected to each of the communication terminals, and a balanced two-wire cable connected between each of the branch units. Is a communication system for mutually transmitting and receiving data signals via the splitter and the balanced two-wire cable, wherein the communication terminal generates a modulated wave signal from a data signal to be transmitted and transmits the modulated wave signal to the balanced two-wire cable. A signal transmitting unit for transmitting, a transmission signal receiving unit for receiving the own modulated wave signal transmitted by the signal transmitting unit and demodulating the signal to obtain a data signal, and a modulated wave signal from the balanced two-wire cable. The transmission signal receiving unit for receiving and demodulating the data signal to obtain a data signal, and comparing the respective data signals received and demodulated by the transmission signal receiving unit and the transmission signal receiving unit to obtain the balanced 2 Line A signal collision detection unit that detects a collision of data signals on the cable, wherein the branch unit connects to the communication terminal with a pair of feed terminal units for connecting to the balanced two-wire cable. And a branch circuit unit, the branch circuit unit being interposed between both lines between the pair of feed terminal units and the branch terminal unit, and being high with respect to the balanced two-wire cable. It is composed of a pair of resistors serving as impedance and a transformer interposed between the pair of resistors and the branch terminal for matching impedance with the balanced two-wire cable. , The insertion loss at the branch point can be reduced, and the impedance between the balanced two-wire cable and the branch unit at the branch point using a transformer By keeping the matching, the attenuation of the modulated wave signal on the balanced two-wire cable can be reduced, so that the effect of the attenuation or reflection of the modulated wave signal is reduced, and in a communication system having a collision detection function, There is an effect that both the maximum values of the transmission distance and the number of branch connections can be increased.
[0067]
According to a second aspect of the present invention, in the first aspect of the present invention, the branching unit amplifies a modulated wave signal from the branch terminal unit with a reception signal amplifier for amplifying a modulated wave signal from the sending terminal unit. And the modulated signal input from the first input / output terminal is distributed and output from the second and third input / output terminals, and input from the second and third input / output terminals. And two hybrid circuits for mixing the modulated wave signal and outputting the mixed wave signal from the first input / output terminal, wherein the first input / output terminal of one of the hybrid circuits is connected to the branch circuit unit and the branch terminal unit. And the first input / output terminal of the other hybrid circuit is connected to the branch terminal portion between the branch circuit portion and the branch terminal portion, and the two hybrid circuits are connected to each other. Between the second and third input / output terminals of the circuit. Since the signal amplifier and the transmission signal amplifier are connected to each other, the data signal can be bidirectionally amplified in the branching device, and the maximum values of both the transmission distance and the number of branch connections can be further increased as compared with the first embodiment. This has the effect.
[0068]
According to a third aspect of the present invention, in the first aspect, the communication terminal distributes the modulated wave signal input from the first input / output terminal and outputs the modulated wave signal from the second and third input / output terminals. A hybrid circuit that mixes the modulated wave signals input from the second and third input / output terminals and outputs the mixed signal from the first input / output terminal; A transmission signal amplifier for amplifying a modulated wave signal from the signal transmission unit between a second input / output terminal of the hybrid circuit and the signal transmission unit; A reception signal amplifier for amplifying a modulated wave signal from the balanced two-wire cable is connected between the third input / output terminal of the transmission signal reception section and the transmission signal reception section. The amplifier, together, Since the modulated wave signal is amplified by the amount of reverse coupling attenuation in the hybrid circuit, the communication terminal can amplify and transmit the data signal without losing the signal collision detection function, and the communication system having the collision detection function There is an effect that both maximum values of the entire transmission distance and the number of branch connections can be increased.
[0069]
According to a fourth aspect of the present invention, in the first aspect, the communication terminal distributes the modulated wave signal input from the first input / output terminal and outputs the modulated wave signal from the second and third input / output terminals. A hybrid circuit that mixes the modulated wave signals input from the second and third input / output terminals and outputs the mixed signal from the first input / output terminal; A transmission signal amplifier for amplifying a modulated wave signal from the signal transmission unit between a second input / output terminal of the hybrid circuit and the signal transmission unit; And the transmission signal amplifier amplifies the modulated wave signal by the amount of reverse coupling attenuation in the hybrid circuit, so that a signal collision detection function is provided. Without losing Since a data signal having a high level with respect to noise can be transmitted before transmission and a signal-to-noise ratio (S / N ratio) can be improved, a more reliable and high-quality communication system can be realized. Since the number of amplifiers for amplifying the data signal can be reduced, the cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a system configuration of a communication system according to a first embodiment.
FIG. 2 is a block diagram illustrating a configuration of a communication terminal according to the first embodiment.
FIG. 3 is a block diagram showing a configuration of a branching device of the above.
FIG. 4 is a block diagram illustrating a configuration of a communication terminal of a communication system according to a second embodiment.
FIG. 5 is a block diagram showing a configuration of a branching device of the above.
FIG. 6 is an explanatory diagram for explaining a main part of the above.
FIG. 7 is a block diagram illustrating a configuration of a communication terminal of a communication system according to a third embodiment.
FIG. 8 is a block diagram illustrating a configuration of a communication terminal of a communication system according to a fourth embodiment.
FIG. 9 is a block diagram showing a system configuration of a conventional communication system.
[Explanation of symbols]
1 communication terminal
1a 2-wire 4-wire conversion circuit
1b Signal transmission unit
1c Transmission signal receiving unit
1d transmission signal receiver
1e Signal collision detector
1f CPU unit
1g power supply
1h internal power supply
1i terminal
1j DC power supply superposition section
1k hybrid circuit
1l transmission signal amplifier
1m receive signal amplifier
2 Switch
2a, 2b feed terminal
2c Branch terminal
2d branch circuit
2e, 2f hybrid circuit
2g Receive signal amplifier
2h transmission signal amplifier
2i DC power separation unit
2j Internal power supply
C1, C2 balanced 2-wire cable
Z terminal member

Claims

A plurality of communication terminals, a branch unit connected to each of the communication terminals, and a balanced two-wire cable connected between the branch units; A communication system for mutually transmitting and receiving data signals via a two-wire cable, wherein the communication terminal generates a modulated wave signal from a data signal to be transmitted and transmits the modulated wave signal to the balanced two-wire cable; A transmission signal receiving section that receives the own modulated wave signal transmitted by the signal transmitting section and demodulates the modulated signal to obtain a data signal, and receives a modulated wave signal from the balanced two-wire cable and demodulates the same. A transmission signal receiving unit for obtaining a data signal, and a data signal on the balanced two-wire cable are compared by comparing respective data signals received and demodulated by the transmission signal receiving unit and the transmission signal receiving unit. A signal collision detection unit for detecting a collision of the transmission line, wherein the branch unit includes a pair of feed terminal units for connecting to the balanced two-wire cable, and a branch terminal unit for connecting the branch unit to the communication terminal. And a branch circuit portion, wherein the branch circuit portion is provided between the two lines between the pair of feed terminal portions and the branch terminal portion and has a pair of high impedance with respect to the balanced two-wire cable. A communication system comprising: a resistor; and a transformer interposed between the pair of resistors and the branch terminal for matching impedance with the balanced two-wire cable.

The branching unit is a reception signal amplifier that amplifies a modulated wave signal from the sending terminal unit, a transmission signal amplifier that amplifies a modulated wave signal from the branch terminal unit, and input from a first input / output terminal. The modulated wave signal is distributed and output from the second and third input / output terminals, and the modulated wave signals input from the second and third input / output terminals are mixed to form the first input / output terminal. , And a first input / output terminal of one of the hybrid circuits is connected to the branch circuit unit side between the branch circuit unit and the branch terminal unit, and the other hybrid circuit is connected to the other hybrid circuit. A first input / output terminal of a circuit is connected to the branch terminal between the branch circuit and the branch terminal, and a second input / output terminal of the two hybrid circuits is connected to the second input / output terminal of the hybrid circuit. The connection between the reception signal amplifier and the transmission signal amplifier Communication system according to claim 1, wherein.

The communication terminal distributes the modulated wave signal input from the first input / output terminal, outputs the modulated wave signal from the second and third input / output terminals, and outputs the modulated wave signal input from the second and third input / output terminals. A hybrid circuit that mixes a wave signal and outputs the mixed signal from the first input / output terminal. The first input / output terminal of the hybrid circuit is connected to the balanced two-wire cable. A transmission signal amplifier for amplifying the modulated wave signal from the signal transmission unit is connected between the output terminal and the signal transmission unit, and a third input / output terminal of the hybrid circuit and the transmission signal reception unit are connected to each other. A reception signal amplifier for amplifying the modulated wave signal from the balanced two-wire cable, and the transmission signal amplifier and the reception signal amplifier collectively have a reverse coupling attenuation amount in the hybrid circuit. Only mutated Communication system according to claim 1, wherein the amplifying the wave signal.

The communication terminal distributes the modulated wave signal input from the first input / output terminal, outputs the modulated wave signal from the second and third input / output terminals, and outputs the modulated wave signal input from the second and third input / output terminals. A hybrid circuit that mixes a wave signal and outputs the mixed signal from the first input / output terminal. The first input / output terminal of the hybrid circuit is connected to the balanced two-wire cable. A transmission signal amplifier that amplifies a modulated wave signal from the signal transmission unit is connected between an output terminal and the signal transmission unit, and a third input / output terminal of the hybrid circuit and the transmission signal reception unit are connected. The communication system according to claim 1, wherein the communication signal amplifier is configured to be connected, and the transmission signal amplifier amplifies the modulated wave signal by an amount of reverse coupling attenuation in the hybrid circuit.