JP2004128629A

JP2004128629A - Signaling circuit

Info

Publication number: JP2004128629A
Application number: JP2002286616A
Authority: JP
Inventors: Kazutomo Souma; 相馬　一等
Original assignee: NEC Engineering Ltd
Current assignee: NEC Engineering Ltd
Priority date: 2002-09-30
Filing date: 2002-09-30
Publication date: 2004-04-22

Abstract

<P>PROBLEM TO BE SOLVED: To provide a signaling circuit in which the output from a receiving circuit is prevented from unsettling. <P>SOLUTION: The signaling circuit comprises a cable 50 including a signal line for transmitting a balanced signal 101 and a signal line for transmitting an omission monitor signal 107, a terminal board 11-1 for connecting the cable 50 on the transmission circuit side, a driver 10 for receiving an unbalanced signal 100 and outputting the balanced signal 101 to the terminal board 11-1, a short-circuit line 12-1 for sending back the omission monitor signal 107, a terminal board 21-1 for connecting the cable 50 on the receiving circuit side, a receiver 20 for receiving the balanced signal 101 and outputting an unbalanced signal 102, and a current loop detection circuit 105 for connecting a signal line 22-1 with the signal line of the omission monitor signal 107 through a terminal board 21-1 in order to monitor connection of the transmitting circuit side with the cable 50 through the signal line 22-1 and inputting a control signal 106 to the gate terminal of the receiver 20. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は信号伝送回路に関し、特に平衡伝送路による信号を送受信する送信回路と受信回路とで構成される信号伝送回路に関する。
【０００２】
【従来の技術】
この種の従来の技術について特許文献を基に説明する。
【０００３】
第１の従来の信号伝送回路は、ＥＣＬ信号をバランス方式で出力するドライバＩＣと、この出力信号を入力するレシーバＩＣとの間で、ドライバＩＣ側が電源断となった時レシーバＩＣをハイレベルに固定することにより、レシーバＩＣの出力信号が不安定になることを防止する構成になっている（特許文献１参照）。
【０００４】
第２の従来例の信号伝送回路は、受信回路の平衡信号の終端方法として、差動入力端子間に一定のオフセット電位を印加することにより、インタフェースの障害時に対して、受信回路の不平衡信号の出力電位を一定電位に確定させるようにしたオフセット電位印加手段を具備したフェール・セーフ回路の構成になっている（特許文献２参照）。
【０００５】
【特許文献１】
特開平５−３３５９３２号公報（第２頁〜第３頁、図１）
【特許文献２】
特開昭５６−１５２３５７号公報（第２頁〜第３頁。第２図、第３図）
【０００６】
【発明が解決しようとする課題】
近年、信号伝送路に対する信号伝送回路においては、伝送速度の高速化、低消費電力化、不要波雑音放射レベルの低減面から、従来から使用されてきた＋５Ｖ駆動、＋３．３Ｖ駆動のＲＳ−４２２規格に適合したデバイスで構成した送信回路、受信回路は採用できない状態になってきた。
【０００７】
このため、近年の高速信号伝送のために開発されたＴＩＡ／ＥＩＡ−６４４で規格化されたデータ伝送方式のＬＶＤＳ（Ｌｏｗ　Ｖｏｌｔａｇｅ　Ｄｉｆｆｅｒｅｎｔｉａｌ　Ｓｉｇｎａｌｉｎｇ）デバイスで送信回路、受信回路を構成する必要が出てきた。このデバイスを採用することで、高速信号伝送と消費電力、不要波雑音放射レベルの低減が実現できる。
【０００８】
ＬＶＤＳデバイスの例としては、例えばＤＳ９０ＬＶ０３２ＡＴＭ（／／ｗｗｗ・ｎａｔｉｏｎａｌ．ｃｏｍ／ａｄｓ−ｃｇｉ／ｖｉｅｗｅｒ．ｐｌ／ＪＰＮ／ｄｓ／ＤＳ／ＤＳ９０ＬＶ０３２．ｐｄｆ）があり、これは、２００ｍＶ〜８００ｍＶの低振幅で２５０ＭＨｚ程度の高速信号を伝送できるデバイスである。現在では更に高速動作（１ＧＨｚを超える）するデバイスも開発されている。
【０００９】
ＬＶＤＳは理想的は環境下では、低振幅の電圧変化の差動信号で高速なデータを伝送でき、差動モードを維持すれば外部からのノイズに強いが、実際は周辺の＋５Ｖや＋３．３Ｖの信号と隣接する影響によるコモンモードノイズを十分除去できない場合があり、この場合に信号伝送誤りが発生する。このため、送信回路、受信回路のみならず、伝送ラインの信号パターン配線や、ケーブル接続上の信号グルーピングや、デバイス供給電源の分離などの配慮が必須であった。
【００１０】
そこで、上記第１及び第２の従来例に信号を伝送できる低振幅の差動信号を使用するＬＶＤＳデバイスを送受信回路に適用した場合に、上記伝送ラインの信号パターン配線や、ケーブル接続上の信号グルーピング、デバイス供給電源の分離等の十分に配慮できた理想的な環境ならば、前記第２の従来例のフェール・セーフ機能により送信回路側の電源断になったときや、受信側でケーブルが未接続になった場合には、受信回路の不平衡信号を一定電位に確定して、出力信号が不安定になることを防止することができるが、現実には電源やグラウンド（ＧＮＤ）からの雑音が前記差動信号へ異なった位相、レベルで影響することにより受信回路の出力が不安定な状態になる場合がある。
【００１１】
さらに、送信回路側でケーブルが未接続になった場合には、ケーブルがアンテナの役割となり、他からの干渉信号の影響を受けて、低振幅の差動電位差で動作する受信回路の出力が固定できない不具合が生じる。
【００１２】
また、前記送受信信号以外の別の信号が同一ケーブルで共に伝送されている場合には、送信回路が未接続になった場合でも、別の信号がケーブル上を伝送されており、この信号からの影響で前記受信回路の出力が固定できない不安定な状態が生じる。
【００１３】
［発明の目的］
本発明の目的は、ＬＶＤＳ等の低振幅で高速信号伝送を可能とする平衡伝送路の信号伝送回路を提供すると共に更に、低減振幅差動信号を装置間伝送に採用された場合に、送信回路がケーブルから外れた場合や、ケーブルが開放した場合を監視して、受信回路の不平衡信号出力が不安定になることを防止し、更にまた、低消費電力化、不要波雑音放射レベルが低減された信号伝送回路を提供することにある。
【００１４】
【課題を解決するための手段】
本発明の信号伝送回路は、不平衡信号を受信して平衡信号に変換し、１対の信号線を介して前記平衡信号を送出する送信号回路と、前記１対の信号線からの前記平衡信号を伝送するケーブルと、前記ケーブルからの前記平衡信号を終端し、前記不平衡信号に変換して出力する受信回路とを備える信号伝送回路において、前記送信回路側の前記１対の信号線が前記ケーブルに接続されたかを監視する監視信号を前記受信回路側から前記ケーブルの監視信号線を介して前記送信回路側と前記受信回路側とを接続して監視信号を送出して検出し、その検出結果に基づく制御信号によって前記受信回路から前記不平衡信号の送出を可能にし、前記接続監視手段は、前記受信回路側に前記接続の監視のための前記監視信号の電流を前記ケーブルの１対の前記監視信号線へ送出して前記送信回路からの折り返しの前記監視信号の電流を検出すると前記制御信号を送出する監視電流ループ検出回路と、前記送信回路側に、前記平衡信号を送出する前記１対の信号線が前記平衡信号を伝送する前記ケーブルに接続されたときに、前記ケーブル内の前記１対の監視信号線に接続して前記送信回路内で短絡させる短絡線とを有し、又は、前記接続監視手段は、前記送信回路側と前記受信回路側との間に、前記平衡信号を送出する前記１対の信号線が前記平衡信号を伝送する前記ケーブルに接続されたときに、前記ケーブル内の前記の監視信号線に接続して前記送信回路内で接地させる接地線と、前記受信回路内に前記ケーブルの前記接地された前記監視信号線に接続して地気の前記制御信号を前記受信回路へ送出する第１の信号線とを有し、又は、前記接続監視手段は、前記送信回路側と前記受信回路側との間に、前記平衡信号を送出する前記１対の信号線が前期平衡信号を伝送する前記ケーブルに接続された時に、前記ケーブル内の前記監視信号線に接続して前記送信回路内で接地させる第１の接地線と、前記受信回路内に前記ケーブルの第１の前記接地させた第１の前記監視信号線に接続して、第１の前記信号線を前記受信回路へ送出する第１の制御信号により受信デバイスの平衡信号の出力を制御する。また、前記受信回路内で接地させる第２の接地線と、前記受信回路内に前記ケーブルの第２の前記接地させた第２の前記監視信号線に接続して第２の前記信号線を前記送信回路へ送出する第２の制御信号により送信デバイスの平衡信号の出力を制御する。さらに、前記受信回路は前記制御信号の入力を可能にする制御信号入力端子付きの平衡−不平衡変換Ｌｏｗ　Ｖｏｌｔａｇｅ　Ｄｉｆｆｅｒｅｎｔｉａｌ　Ｓｉｇｎａｌｉｎｇ　デバイスで構成され、前記送信号回路は前記第２の制御信号の入力を可能にする制御信号入力端子付不平衡−平衡変換Ｌｏｗ　Ｖｏｌｔａｇｅ　Ｄｉｆｆｅｒｅｎｔｉａｌ　Ｓｉｇｎａｌｉｎｇ　デバイスで構成されている。
【００１５】
本発明の信号伝送回路は、不平衡信号を受信して平衡信号に変換し１対の信号線を介して前記平衡信号を送出す送信回路と、前記１対の信号線からの前記平衡信号を伝送するケーブルと、前記ケーブルからの前記平衡信号を終端し、前記不平衡信号に変換して出力する受信回路とを備える信号伝送回路において、
前記受信回路側に、前記送信回路側の前記１対の信号線が前記ケーブルに接続したか未接続かまたは前記１対の信号線を使用するか未使用かの情報を基に人為的に制御信号の送出を設定する設定手段を有し、前記制御信号の入力の有無によって前記受信回路の送出信号の有効か無効かを決定させ、前記設定手段は前記送信回路側の前記１対の信号線が前記ケーブルに接続して前記制御信号を送出する時間帯を予め設定できるタイマを有し、前記受信回路は前記制御信号の入力を可能にする制御信号入力端子付きの平衡−不平衡変換Ｌｏｗ　Ｖｏｌｔａｇｅ　Ｄｉｆｆｅｒｅｎｔｉａｌ　Ｓｉｇｎａｌｉｎｇ　デバイスで構成され、前記送信回路は前記第２の制御信号の入力を可能にする制御信号入力端子付不平衡−平衡変換Ｌｏｗ　Ｖｏｌｔａｇｅ　Ｄｉｆｆｅｒｅｎｔｉａｌ　Ｓｉｇｎａｌｉｎｇデバイスで構成されている。
【００１６】
【発明の実施の形態】
次に、本発明について図面を参照して説明する。
【００１７】
図１は本発明の第１の実施の形態の信号伝送回路の構成を示すブロック図である。
【００１８】
図１において、本第１の実施の形態の信号伝送回路は、平衡信号１０１を伝送する二本の信号線および抜け監視信号１０７を伝送する二本の信号線を含んだケーブル５０と、送信回路側のケーブル５０を接続する端子盤１１−１と、不平衡信号１００を受信して端子盤１１−１に平衡信号１０１を出力するドライバ１０と、端子盤１１−１内の二つの端子を短絡させて抜け監視信号１０７を返送させる短絡線１２−１と、受信回路側のケーブル５０を接続する端子盤２１−１と、端子盤２１−１から平衡信号１０１を伝送する信号線２２−２の前記正極信号（＋）と負極信号（−）を終端する終端抵抗１０３と、平衡信号１０１を受信して不平衡信号１０２を出力するレシーバ２０と、不平衡信号１０２の信号線をプルアップさせる抵抗１０４と、信号線２２−１を抜け監視信号１０７の信号線に端子盤１２−１を介して接続して送信回路側がケーブル５０に接続されているか又は抜けているか、信号線２２−１を介して監視し、監視結果を制御信号１０６としてレシーバ２０のゲート端子に入力する電流ループ検出回路１０５とを有している。
【００１９】
この第１の実施の形態におけるレシーバ２０は、ドライバ１０からのケーブル５０を介して平衡信号１０１を不平衡信号１０２に変換し、そのレシーバ２０の出力の不平衡信号１０２を電流ループ検出回路１０５からの制御信号１０６によって、ハイインピーダンスに制御できる制御信号入力端子付きのＬＶＤＳデバイスが用いられている。
【００２０】
次に、本第１の実施の形態の動作について図１を参照して説明する。
【００２１】
予め、平衡信号１０１および抜け監視信号１０７を伝送するそれぞれが一対になっている回線を有するケーブル５０が、送信回路側及び受信回路側のそれぞれの端子盤１１−１，１２−１に、例えばコネクタを介して接続されているものとする。
【００２２】
また、受信回路側においてもレシーバ２０の入力側から平衡信号１０１を受信するための信号線２２−２と、電流ループ検出回路１０５からの信号線２２−１とが一緒になっているケーブルのコネクタを介して、端子盤２１−１でケーブル５０のコネクタに接続されている。
【００２３】
送信回路側においては、ドライバ１０の出力側から正極信号（＋）及び負極信号（−）を有した平衡信号１０１の１対の信号線１２−２と、抜け監視信号１０７を折り返すための短絡線１２−１とが一緒になっているケーブルのコネクタを介して端子盤１１−１でケーブル５０のコネクタに接続できる構成になっている。
【００２４】
即ち、本第１の実施の形態の信号伝送回路においては。送信回路側では端子盤１１−１でケーブル５０のコネクタとドライバ１０の出力の信号線１２−２及び短絡線１２−１を有しているケーブルのコネクタとが接続されるので、ドライバ１０の出力信号線１２−２と短絡線１２−１とが必ず同時に接続される構成になっている。
【００２５】
従って、送信回路側で、ドライバ１０の出力の信号線１２−２が端子盤１１−１でコネクタを介してケーブル５０に接続されると、同時に短絡線１２−１もケーブル５０が接続され、電流ループ検出回路１０５からのドライバ１０の出力がケーブル５０との接続外れがないかを監視する抜け監視信号１０７の電流が短絡線１２−１の折り返しによって流れ、例えば、ホトカプラ等のデバイスで構成された電流ループ監視回路１０５は、その折り返しの電流を検出することによって、ケーブル５０が端子盤１１−１、２１−１間で正常に接続されてレシーバ２０で受信する平衡信号は有効と判定することができる。
【００２６】
有効と判定した時、電流ループ検出回路１０５出力である制御信号１０６の電位はロー　Ｌ　になり、レシーバ２０は入力した平衡信号１０１を不平衡信号１０２に変換して出力する。
【００２７】
もし、無効と判定した時には、電流ループ検出回路１０５の出力である制御信号１０６の電位はハイ（Ｈ）として、レシーバ２０の出力をハイインピーダンスに制御し、平衡信号１０１の入力を無効にする。レシーバ２０がハイインピーダンスに制御されたときには、出力端子に接続されている抵抗１０４がレシーバ２０の電源電圧であるＶｃｃにプルアップされている構成であるため、不平衡信号１０２の出力電位をハイ（Ｈ）の電位に確定する。例えば、平衡信号１０１の入力が同一ケーブル内の他信号からの雑音の影響を受けていても、雑音による影響を遮断し、レシーバ２０の出力電圧をハイ（Ｈ）固定にしたことにより無効とされる。
【００２８】
もし、レシーバ２０がハイインピーダンスに制御されたときに、不平衡信号１０２をロー（Ｌ）電位に固定したい場合には、抵抗１０４を接地（ＧＮＤに接続）することで実現できる
次に、本発明の第２の実施の形態の信号伝送回路について説明する。
【００２９】
図２は本発明の第２の実施の形態の信号伝送回路の構成を示すブロック図である。
【００３０】
本第２の実施の形態の信号伝送回路においては図１に示した第１の実施の形態の信号伝送回路と相違する場合のみについて説明する。
【００３１】
図２において、本第２の実施の形態の信号伝送回路は、ドライバ１０の入力信号の不平衡信号１００が平衡信号１０１に変換されてケーブル５０を経由してレシーバ２０で受信され、不平衡信号１０２に再び変換される系統のシステム構成は第１の実施の形態と同じであり、ドライバ１０及びレシーバ２０のそれぞれのデバイスも第１の実施の形態の場合と同じである。
【００３２】
異なる部分は、平衡信号１０１が伝送される信号線２２−２が接続されているコネクタ２１−２で、レシーバ２０の制御信号入力端子に接続する抵抗１０９がレシーバ２０の電源電圧であるＶｃｃにプルアップされた信号線２３がケーブル５０内の抜け監視信号１０８伝送用の信号線に接続している点である。
【００３３】
本発明の第１の実施形態と第２の実施形態の相違点は、図１では受信回路への入力電流による有効、無効判定であったのに対して、図２は受信回路への入力電圧による有効，無効判定である。
【００３４】
また、送信回路側においては、信号線１２−２が接続されているコネクタに、ケーブル５０内の抜け監視信号１０８を共に接続し、そこに送信回路側内で接地ＧＮＤ　された接続線１３が接続されている。
【００３５】
次に、本第２の実施の形態の信号伝送回路の受信回路側における受信信号の有効，無効の判定動作について図２を参照して説明する。
【００３６】
図２において、第１の実施の形態の場合と同様に、送信回路側で、ドライバ１０の出力の信号線１２−２が端子盤１１−２でコネクタを介してケーブル５０に接続されると、同時に接地線１３がケーブル５０内の抜け監視信号１０８の伝送線に接続される。
【００３７】
その結果、送信回路で接地された接続線１３はケーブル５０内の抜け監視信号１０８伝送用信号線を介して受信回路側の信号線２３に接続され、接地信号は制御信号１０６としてロー　Ｌ　の信号をレシーバ２０の制御信号入力端子に入力され、レシーバ２０で受信する平衡信号は有効だと判定することができる。
【００３８】
もし、送信回路側で信号線１２−２及び接地線１３を含んだケーブルが端子盤１１−２に接続されない場合には、信号線２３に対して抵抗１０９がレシーバ２０の電源電圧であるＶｃｃへプルアップした構成であるため、制御線１０６はハイ（Ｈ）電位に固定されることで、第１の実施の形態の場合と同様に無効だと判定する。
【００３９】
次に、本発明の第３の実施の形態の信号伝送回路について説明する。
【００４０】
図３は、本発明の第３の実施の形態の信号伝送回路の構成を示すブロック図である。
【００４１】
本第３の実施の形態の信号伝送回路においては、図１，図２に示した第１，第２の実施の形態の信号伝送回路と相違する部分のみについて説明する。
【００４２】
図３において、本第３の実施の形態の信号伝送回路は、ケーブル５０を介してドライバ１０と制御信号入力端子付きのレシーバ２０とが平衡信号１０１を介して接続されたシステム系統は第１，第２の実施の形態と同じである。
【００４３】
異なる部分は、レシーバ２０の出力信号の使用，未使用の制御機能を人為的に設定することができる機能を有した使用，未使用判定回路１３０を有し、その出力が制御信号１０６としてレシーバ２０の制御信号入力端子に入力する構成になっている。
【００４４】
この第３の実施の形態の信号伝送回路においては、例えば、送信回路側を保守する場合に、ドライバ１０の出力の信号線１２−２を有するコネクタを端子盤１１−３から外す前に、受信回路側に連絡して人為的に予め使用・未使用判定回路１３０を未使用の制御信号１０６を出力するように設定することにより、未使用を制御するハイ（Ｈ）電位の制御信号１０６によって、レシーバ２０の出力をハイインピーダンスに制御することができる。これにより、レシーバ２０の出力端子に抵抗１０４がレシーバ２０の電源電圧であるＶｃｃへプルアップした構成から不平衡信号１０２はハイ（Ｈ）電位に固定でき、ドライバ１０の接続外れによるレシーバ２０の受信信号の再生誤りによる後続回路の誤動作を防止することができる。
【００４５】
また、保守以外の場合においても、この送信、受信回路を将来使用する可能性があるものの現時点では使用しない場合で、不平衡信号１００に不定のデータが伝送されてきた状態においても、使用・未使用判定回路１３０を未使用に人為的に設定することで、レシーバ２０の出力を固定することができるため後続の回路の誤動作を防止することができる。
【００４６】
この他に、使用・未使用判定回路１０３内にタイマを備え、この信号伝送回路全体の使用時間帯又は未使用時間帯を人為的に設定することによっても、レシーバ２０の有効無効を設定することができる。さらに、この信号伝送回路が複数である場合には、各信号伝送回路の使用・未使用判定回路１３０を同期制御することで使用時間帯を制御することで伝送ルートの時分割切替制御が可能になる。
【００４７】
次に、本発明の第４の実施の形態の信号伝送回路について説明する。
【００４８】
図４は本発明の第４の実施の形態の信号伝送回路の構成を示すブロック図である。
【００４９】
本第４の実施の形態の信号伝送回路においては、図２に示した第２の実施の形態の信号伝送回路と相違する部分のみについて説明する。
【００５０】
図４において、本第４の実施の形態の信号伝送回路は、図２に示す第２の実施の形態の信号伝送回路と比較した場合に、送信回路側において信号線１２−２及び接地線１３有するケーブルのコネクタが端子盤１１−４に接続すると共に、ドライバ３０の出力制御端子に接続した制御線１１６を抵抗１１９でドライバ３０の電源電圧であるＶｃｃにプルアップした信号線１４を端子盤１１−４へ接続する。端子盤１１−４を介して信号線１４は抜け監視信号１１８と接続される。また抜け監視信号１１８は平衡信号１０１や抜け監視信号１０８とともにケーブル５０に含まれている。抜け監視信号１１８はケーブル５０により受信回路側の接地（ＧＮＤ）情報に接続され、また、受信回路側においては、接地信号線２４が接地（ＧＮＤ）されてコネクタに接続されていると共に、信号線２２−２及び信号線２３を有するケーブルのコネクタが端子盤２１−４に接続する。このように、受信回路側の接地情報により、送信回路側内のドライバ３０の使用・未使用が制御できる構成である。受信回路側が未実装の場合には、信号線１２−２を送信する必要がないことができる機能を有した使用，未使用判定回路１３０を有し、その出力が制御信号１０６としてレシーバ２０の制御信号入力端子に入力する構成になっている。
【００５１】
即ち、第２、第４の実施の形態の相違点は、送信回路側及び受信回路側のそれぞれのコネクタが端子盤１１−４、２１−４を介してケーブル５０に接続されると、レシーバ２０の制御信号入力端子に、第２の実施の形態の場合と同様に送信回路側の接地信号　ＧＮＤ　が抜け監視信号１０８となり、それが制御信号１０６として入力されると同時に、本第４の実施の形態の場合においては、受信回路側の接地信号　ＧＮＤ　が抜け監視信号１１８となり、それが制御信号１１６としてドライバ３０の制御入力端子に入力される。
【００５２】
この結果、第２の実施の形態の信号伝送回路におけるレシーバ２０と同様に、レシーバ２０の出力の不平衡振動１０２は有効信号として出力される。
【００５３】
このように、本第４の実施の形態では、入力された不平衡信号１００を平衡信号１０１へ変換するドライバ３０に平衡出力信号をハイインピーダンスに制御できる制御機能付きの不平衡−平衡変換デバイスを用い、抜け監視信号１１８によりレシーバ２０がケーブル５０に接続されて、かつ送信回路側に接続している時に信号出力を有効と判定して制御信号１１６によって平衡信号１０１を出力する。
【００５４】
また、レシーバ２０がケーブル５０に接続されていない時や、ケーブル５０が送信回路側の端子盤１１−４に接続されていない時には、受信信号は無効となると共に、送信信号も無効となるため、本信号伝送は無効と判定することになる。したがって、必要な平衡信号１０１をドライバ３０から出力しないように、抵抗１１９をドライバ３０の電源電圧であるＶｃｃにプルアップすることでドライバ３０の制御機能でハイインピーダンスに制御し、不要な信号をケーブル５０から送出しないことでＥＭＩ放射レベルを低減できる機能を有することができる。
【００５５】
尚、上記第１〜第４の実施の形態のそれぞれにおいて、送信回路側のドライバ１０，３０を含む回路と受信回路側のレシーバ２０と電流検出回路１０５を含む回路とはそれぞれ１枚のプリント配線基板内で構成され、端子盤１１−１，２１−１はそれぞれこれらのプリント配線基板が挿抜できるコネクタと考え、このコネクタに予めケーブル５０が接続されているものと考えてもよい。この場合、送信回路側又は受信回路側のプリント配線基板がコネクタとの挿抜によってケーブルとの接，不接を考えることができる。この場合、プリンが配線基板がコネクタから抜ければ、抜け監視信号１０７，１０８，１１８により、本信号伝送は無効と判定されることになる。
【００５６】
【発明の効果】
以上説明したように本発明は不平衡信号を受信して平衡信号に変換し、１対の信号線を介して前記平衡信号を送信する送信回路と、１対の信号線からの平衡信号を伝送するケーブルとケーブルからの平衡信号を終端し、不平衡信号に変換して出力する受信回路とを備える信号伝送回路において、送信回路側の１対の信号線がケーブルに接続されたかを監視する監視信号を受信回路側からケーブル監視信号線を介して、送信回路側へ送信し、ケーブルとの接続を検出するとその検出結果に基づく制御信号によって、受信回路から不平衡信号の送出を可能なせる接続監視手段を有することにより以下に示す効果がある。
【００５７】
第１に、送信回路側がケーブルに接続されるのを監視しているので、受信回路の出力として有効無効を判定して信号を送出できる効果がある。
【００５８】
第２に、送信回路がケーブルに接続されていない場合や、ケーブルの開放時に受信回路の出力が不安定になることを防止できる効果がある。
【００５９】
第３に、受信回路との接続を監視することで、不要な信号をケーブルから送出しないことでＥＭＩ放射レベルを低減できる効果がある。
【００６０】
第４は、高速信号伝送を実現するＬＶＤＳデバイスで、より高速に信号を伝送するための低振幅差動平衡信号を伝送するとき、第１から第３の効果を伴う高速信号伝送が可能となり、受信回路の出力の不安定を防止する効果がある。
【００６１】
第５は、送信回路及び受信回路に低振幅差動信号（ＬＶＤＳ）を伝送するデバイスを採用することにより、低消費電力化や不要な波雑音放射レベルを低減させることが効果がある。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態の信号伝送回路の構成を示すブロック図である。
【図２】本発明の第２の実施の形態の信号伝送回路の構成を示すブロック図である。
【図３】本発明の第３の実施の形態の信号伝送回路の構成を示すブロック図である。
【図４】本発明の第４の実施の形態の信号伝送回路の構成を示すブロック図である。
【符号の説明】
１０，３０　　ドライバ
２０　　レシーバ
１１−１、１１−２、１１−３、１１−４、２１−１、２１−２、２１−３、２１−４　　端子盤
５０　　ケーブル
１０３　　終端抵抗
１０４、１０９、１１９　　抵抗
１００、１０２　　不平衡信号
１０１　　平衡信号
１０５　　電流ループ検出回路
１０６、１１６　　制御信号
１０７、１０８、１１８　　抜け監視信号
１３０　　使用・未使用判定回路[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a signal transmission circuit, and more particularly to a signal transmission circuit including a transmission circuit and a reception circuit for transmitting and receiving a signal through a balanced transmission path.
[0002]
[Prior art]
This type of conventional technology will be described based on patent documents.
[0003]
A first conventional signal transmission circuit sets a receiver IC between a driver IC that outputs an ECL signal in a balanced manner and a receiver IC that inputs the output signal when the driver IC is turned off. By fixing, the output signal of the receiver IC is prevented from becoming unstable (see Patent Document 1).
[0004]
The signal transmission circuit according to the second prior art applies a constant offset potential between the differential input terminals as a method of terminating the balanced signal of the receiving circuit. A fail-safe circuit is provided with an offset potential applying means for fixing the output potential of the circuit to a constant potential (see Patent Document 2).
[0005]
[Patent Document 1]
JP-A-5-335932 (pages 2 to 3, FIG. 1)
[Patent Document 2]
JP-A-56-152357 (pages 2 to 3; FIGS. 2 and 3)
[0006]
[Problems to be solved by the invention]
In recent years, in a signal transmission circuit for a signal transmission line, RS-422 of +5 V drive and +3.3 V drive conventionally used from the viewpoint of increasing transmission speed, reducing power consumption, and reducing unnecessary wave noise emission level. Transmitter circuits and receiver circuits composed of devices conforming to the standard have become unable to be adopted.
[0007]
For this reason, it has become necessary to configure a transmission circuit and a reception circuit with an LVDS (Low Voltage Differential Signaling) device of a data transmission method standardized by TIA / EIA-644 developed for recent high-speed signal transmission. . By adopting this device, high-speed signal transmission, power consumption, and reduction of unnecessary wave noise emission level can be realized.
[0008]
An example of an LVDS device is, for example, DS90LV032 ATM (//www.national.com/ads-cgi/viewer.pl/JPN/ds/DS/DS90LV032.pdf), which has a low amplitude of 200 mV to 800 mV and 250 MHz. It is a device that can transmit high-speed signals of the order. At present, devices that operate at higher speeds (over 1 GHz) are also being developed.
[0009]
In an ideal environment, the LVDS can transmit high-speed data with a differential signal having a low-amplitude voltage change and is resistant to external noise if the differential mode is maintained. However, in reality, the surrounding + 5V or + 3.3V In some cases, common mode noise due to the influence adjacent to the signal cannot be sufficiently removed. In this case, a signal transmission error occurs. For this reason, not only the transmission circuit and the reception circuit but also the signal pattern wiring of the transmission line, the signal grouping on the cable connection, the separation of the device power supply, and the like have been indispensable.
[0010]
Therefore, when an LVDS device using a low-amplitude differential signal capable of transmitting a signal is applied to the transmitting and receiving circuit in the first and second conventional examples, the signal pattern wiring of the transmission line and the signal on the cable connection are used. In an ideal environment where sufficient considerations such as grouping and separation of device supply power can be made, when the power is cut off on the transmission circuit side by the fail safe function of the second conventional example, or when the cable is When the connection is not established, the unbalanced signal of the receiving circuit is fixed at a constant potential to prevent the output signal from becoming unstable. However, in reality, the output signal from the power supply or the ground (GND) can be prevented. When the noise affects the differential signal in different phases and levels, the output of the receiving circuit may become unstable.
[0011]
Furthermore, if the cable is disconnected on the transmitting circuit side, the cable acts as an antenna, and the output of the receiving circuit that operates with a low-amplitude differential potential difference is fixed under the influence of interference signals from other sources. Unavailable trouble occurs.
[0012]
Further, when another signal other than the transmission / reception signal is transmitted together on the same cable, another signal is transmitted on the cable even when the transmission circuit is disconnected. Due to the influence, an unstable state occurs in which the output of the receiving circuit cannot be fixed.
[0013]
[Object of the invention]
An object of the present invention is to provide a signal transmission circuit of a balanced transmission line that enables high-speed signal transmission with low amplitude such as LVDS, and furthermore, a transmission circuit when a reduced-amplitude differential signal is adopted for inter-device transmission. Monitors when the cable is disconnected from the cable or when the cable is opened to prevent the output of the unbalanced signal from the receiving circuit from becoming unstable, further reducing power consumption and reducing unnecessary noise radiation levels. To provide a signal transmission circuit.
[0014]
[Means for Solving the Problems]
The signal transmission circuit according to the present invention includes a signal transmission circuit that receives an unbalanced signal, converts the unbalanced signal into a balanced signal, and sends the balanced signal through a pair of signal lines, and the balanced signal from the pair of signal lines. In a signal transmission circuit including a cable for transmitting a signal, and a reception circuit for terminating the balanced signal from the cable, converting the signal into the unbalanced signal, and outputting the signal, the pair of signal lines on the transmission circuit side includes: A monitoring signal for monitoring whether or not the cable is connected is connected to the transmitting circuit side and the receiving circuit side from the receiving circuit side via a monitoring signal line of the cable, and a monitoring signal is transmitted and detected. The receiving circuit enables the unbalanced signal to be transmitted by a control signal based on the detection result, and the connection monitoring means supplies the receiving circuit with a current of the monitoring signal for monitoring the connection by a pair of cables. of A monitoring current loop detection circuit for transmitting the control signal when detecting the current of the monitoring signal returned from the transmission circuit by transmitting the monitoring signal line to the monitoring signal line; and transmitting the balanced signal to the transmission circuit side. A short-circuit line connected to the pair of monitoring signal lines in the cable to short-circuit in the transmission circuit when the pair of signal lines is connected to the cable transmitting the balanced signal; or The connection monitoring means, between the transmission circuit side and the reception circuit side, when the pair of signal lines for transmitting the balanced signal is connected to the cable for transmitting the balanced signal, A ground line connected to the monitoring signal line in the cable and grounded in the transmission circuit, and a ground signal connected to the grounded monitoring signal line of the cable in the reception circuit to control the ground control signal. The receiving times Or a first signal line for transmitting the balanced signal between the transmitting circuit side and the receiving circuit side. A first ground line connected to the monitoring signal line in the cable and grounded in the transmission circuit when connected to the cable for transmitting a signal, and a first ground line of the cable in the reception circuit. The output of the balanced signal of the receiving device is controlled by a first control signal that is connected to the grounded first monitoring signal line and sends the first signal line to the receiving circuit. A second ground line grounded in the receiving circuit; and a second signal line connected to the second grounded second monitoring signal line of the cable in the receiving circuit. The output of the balanced signal of the transmitting device is controlled by the second control signal transmitted to the transmitting circuit. Further, the receiving circuit is constituted by a balanced-unbalanced conversion Low Voltage Differential Signaling device having a control signal input terminal capable of inputting the control signal, and the transmitting signal circuit is capable of inputting the second control signal. And an unbalanced-balanced conversion Low Voltage Differential Signaling device with a control signal input terminal.
[0015]
A signal transmission circuit according to the present invention includes a transmission circuit that receives an unbalanced signal, converts the unbalanced signal into a balanced signal, and sends the balanced signal through a pair of signal lines, and the balanced signal from the pair of signal lines. A signal transmission circuit including a cable to be transmitted and a receiving circuit that terminates the balanced signal from the cable and converts the signal into the unbalanced signal and outputs the signal.
On the receiving circuit side, the pair of signal lines on the transmitting circuit side is artificially controlled based on information on whether the pair of signal lines is connected or not connected to the cable or whether the pair of signal lines is used or not used. Setting means for setting signal transmission, and determining whether the transmission signal of the receiving circuit is valid or invalid based on the presence or absence of the input of the control signal, wherein the setting means sets the pair of signal lines on the transmission circuit side Has a timer that can set a time zone for transmitting the control signal by connecting to the cable, and the receiving circuit has a balanced-unbalanced conversion Low Voltage with a control signal input terminal that enables input of the control signal. A differential signaling device, wherein the transmission circuit has an unbalanced-balanced conversion Low Voltage with a control signal input terminal that enables input of the second control signal. It is composed of a ifferential Signaling device.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a block diagram showing the configuration of the signal transmission circuit according to the first embodiment of the present invention.
[0018]
In FIG. 1, a signal transmission circuit according to the first embodiment includes a cable 50 including two signal lines transmitting a balanced signal 101 and two signal lines transmitting a disconnection monitoring signal 107; Board 11-1 that connects the cable 50 on the side, the driver 10 that receives the unbalanced signal 100 and outputs the balanced signal 101 to the terminal board 11-1, and two terminals in the terminal board 11-1 are short-circuited. The short-circuit line 12-1 for returning the disconnection monitoring signal 107, the terminal board 21-1 for connecting the cable 50 on the receiving circuit side, and the signal line 22-2 for transmitting the balanced signal 101 from the terminal board 21-1. A terminating resistor 103 for terminating the positive signal (+) and the negative signal (-), a receiver 20 for receiving the balanced signal 101 and outputting an unbalanced signal 102, and a resistor for pulling up the signal line of the unbalanced signal 102 10 Through the signal line 22-1 and to the signal line of the monitoring signal 107 via the terminal board 12-1 and whether the transmission circuit side is connected to or disconnected from the cable 50 or via the signal line 22-1. And a current loop detection circuit 105 for monitoring and inputting the monitoring result as a control signal 106 to the gate terminal of the receiver 20.
[0019]
The receiver 20 according to the first embodiment converts the balanced signal 101 into an unbalanced signal 102 via the cable 50 from the driver 10, and converts the unbalanced signal 102 output from the receiver 20 from the current loop detection circuit 105. An LVDS device with a control signal input terminal that can be controlled to a high impedance by the control signal 106 is used.
[0020]
Next, the operation of the first embodiment will be described with reference to FIG.
[0021]
In advance, a cable 50 having a pair of lines for transmitting the balanced signal 101 and the disconnection monitoring signal 107 is connected to the terminal boards 11-1 and 12-1 on the transmission circuit side and the reception circuit side, for example, by using a connector. It is assumed that they are connected via
[0022]
Also, on the receiving circuit side, a signal line 22-2 for receiving the balanced signal 101 from the input side of the receiver 20 and a signal line 22-1 from the current loop detecting circuit 105 are connected together. Through the terminal board 21-1 to the connector of the cable 50.
[0023]
On the transmission circuit side, a pair of signal lines 12-2 of a balanced signal 101 having a positive signal (+) and a negative signal (−) from the output side of the driver 10, and a short-circuit line for returning the disconnection monitoring signal 107 The terminal board 11-1 can be connected to the connector of the cable 50 via the connector of the cable with which the cable 12-1 is connected.
[0024]
That is, in the signal transmission circuit according to the first embodiment. On the transmission circuit side, the terminal board 11-1 connects the connector of the cable 50 to the connector of the cable having the signal line 12-2 and the short-circuit line 12-1 of the driver 10 output. The signal line 12-2 and the short-circuit line 12-1 are always connected at the same time.
[0025]
Therefore, on the transmission circuit side, when the signal line 12-2 of the output of the driver 10 is connected to the cable 50 via the connector at the terminal board 11-1, the short-circuit line 12-1 is also connected to the cable 50 at the same time. The output of the driver 10 from the loop detection circuit 105 monitors whether there is a disconnection with the cable 50, and the current of the disconnection monitoring signal 107 flows due to the return of the short-circuit line 12-1, and is constituted by a device such as a photocoupler. The current loop monitoring circuit 105 determines that the balanced signal received by the receiver 20 when the cable 50 is normally connected between the terminal boards 11-1 and 21-1 is valid by detecting the return current. it can.
[0026]
When it is determined that the signal is valid, the potential of the control signal 106, which is the output of the current loop detection circuit 105, becomes low L, and the receiver 20 converts the input balanced signal 101 into an unbalanced signal 102 and outputs it.
[0027]
If it is determined to be invalid, the potential of the control signal 106, which is the output of the current loop detection circuit 105, is set to high (H), the output of the receiver 20 is controlled to high impedance, and the input of the balanced signal 101 is invalidated. When the receiver 20 is controlled to have a high impedance, the resistor 104 connected to the output terminal is pulled up to Vcc, which is the power supply voltage of the receiver 20, so that the output potential of the unbalanced signal 102 is set to high ( H) is determined. For example, even if the input of the balanced signal 101 is affected by noise from another signal in the same cable, the influence of the noise is cut off and the output voltage of the receiver 20 is fixed to high (H), and thus invalidated. You.
[0028]
If it is desired to fix the unbalanced signal 102 to a low (L) potential when the receiver 20 is controlled to high impedance, this can be realized by connecting the resistor 104 to ground (connected to GND). A signal transmission circuit according to the second embodiment will be described.
[0029]
FIG. 2 is a block diagram showing the configuration of the signal transmission circuit according to the second embodiment of the present invention.
[0030]
In the signal transmission circuit according to the second embodiment, only the case where the signal transmission circuit differs from the signal transmission circuit according to the first embodiment shown in FIG. 1 will be described.
[0031]
In FIG. 2, the signal transmission circuit according to the second embodiment is configured such that an unbalanced signal 100 of an input signal of a driver 10 is converted into a balanced signal 101 and received by a receiver 20 via a cable 50. The system configuration of the system that is converted again into 102 is the same as that of the first embodiment, and the respective devices of the driver 10 and the receiver 20 are also the same as those of the first embodiment.
[0032]
The different part is a connector 21-2 to which a signal line 22-2 for transmitting the balanced signal 101 is connected. A resistor 109 connected to a control signal input terminal of the receiver 20 is pulled to Vcc which is a power supply voltage of the receiver 20. The point that the signal line 23 that has been raised is connected to the signal line for transmitting the disconnection monitoring signal 108 in the cable 50.
[0033]
The difference between the first embodiment and the second embodiment of the present invention is that in FIG. 1 the validity / invalidity is determined by the input current to the receiving circuit, whereas FIG. 2 shows the input voltage to the receiving circuit. Is valid / invalid.
[0034]
On the transmitting circuit side, the disconnection monitoring signal 108 in the cable 50 is connected to the connector to which the signal line 12-2 is connected, and the connection line 13 that is grounded in the transmitting circuit side is connected thereto. Have been.
[0035]
Next, an operation of determining whether a received signal is valid or invalid on the receiving circuit side of the signal transmission circuit according to the second embodiment will be described with reference to FIG.
[0036]
In FIG. 2, when the signal line 12-2 of the output of the driver 10 is connected to the cable 50 via the connector at the terminal board 11-2 on the transmission circuit side, as in the case of the first embodiment, At the same time, the ground line 13 is connected to the transmission line of the disconnection monitoring signal 108 in the cable 50.
[0037]
As a result, the connection line 13 grounded in the transmission circuit is connected to the signal line 23 on the reception circuit side via the disconnection monitoring signal 108 transmission signal line in the cable 50, and the ground signal is used as the control signal 106 as a low L signal. Is input to the control signal input terminal of the receiver 20, and the balanced signal received by the receiver 20 can be determined to be valid.
[0038]
If the cable including the signal line 12-2 and the ground line 13 is not connected to the terminal board 11-2 on the transmission circuit side, the resistor 109 is connected to the signal line 23 to the power supply voltage Vcc of the receiver 20. Since the control line 106 is pulled up, the control line 106 is fixed to a high (H) potential, and thus it is determined that the control line 106 is invalid as in the case of the first embodiment.
[0039]
Next, a signal transmission circuit according to a third embodiment of the present invention will be described.
[0040]
FIG. 3 is a block diagram showing a configuration of the signal transmission circuit according to the third embodiment of the present invention.
[0041]
In the signal transmission circuit according to the third embodiment, only portions different from the signal transmission circuits according to the first and second embodiments shown in FIGS. 1 and 2 will be described.
[0042]
In FIG. 3, the signal transmission circuit according to the third embodiment has a system system in which a driver 10 and a receiver 20 having a control signal input terminal are connected via a cable 50 via a balanced signal 101. This is the same as the second embodiment.
[0043]
The different part has a use / non-use determination circuit 130 having a function of artificially setting a control function of using and not using an output signal of the receiver 20, and an output of which is used as a control signal 106 as a control signal 106. Are input to the control signal input terminal.
[0044]
In the signal transmission circuit according to the third embodiment, for example, when the transmission circuit side is maintained, before removing the connector having the signal line 12-2 of the output of the driver 10 from the terminal board 11-3, the reception is performed. By setting the used / unused determining circuit 130 to output the unused control signal 106 in advance artificially by contacting the circuit side, the high (H) potential control signal 106 for controlling the unused state is used. The output of the receiver 20 can be controlled to high impedance. Thus, the unbalanced signal 102 can be fixed at a high (H) potential from the configuration in which the resistor 104 is pulled up to Vcc, which is the power supply voltage of the receiver 20, at the output terminal of the receiver 20, and the reception of the receiver 20 due to disconnection of the driver 10 Malfunction of the subsequent circuit due to signal reproduction error can be prevented.
[0045]
Further, even in cases other than maintenance, the transmission and reception circuits may be used in the future, but are not used at the present time. By artificially setting the use determining circuit 130 to be unused, the output of the receiver 20 can be fixed, so that malfunction of the subsequent circuit can be prevented.
[0046]
In addition, the validity / invalidity of the receiver 20 can be set by providing a timer in the use / unused determination circuit 103 and artificially setting the use time zone or the unused time zone of the entire signal transmission circuit. Can be. Furthermore, when there are a plurality of signal transmission circuits, time-division switching control of the transmission route is possible by controlling the use time zone by synchronously controlling the use / non-use determination circuit 130 of each signal transmission circuit. Become.
[0047]
Next, a signal transmission circuit according to a fourth embodiment of the present invention will be described.
[0048]
FIG. 4 is a block diagram illustrating a configuration of a signal transmission circuit according to a fourth embodiment of the present invention.
[0049]
In the signal transmission circuit according to the fourth embodiment, only portions different from the signal transmission circuit according to the second embodiment shown in FIG. 2 will be described.
[0050]
In FIG. 4, the signal transmission circuit of the fourth embodiment has a signal line 12-2 and a ground line 13 on the transmission circuit side when compared with the signal transmission circuit of the second embodiment shown in FIG. The connector of the cable is connected to the terminal board 11-4, and the control line 116 connected to the output control terminal of the driver 30 is pulled up to Vcc which is the power supply voltage of the driver 30 by the resistor 119. -4. The signal line 14 is connected to the disconnection monitoring signal 118 via the terminal board 11-4. The disconnection monitoring signal 118 is included in the cable 50 together with the balance signal 101 and the disconnection monitoring signal 108. The disconnection monitoring signal 118 is connected to ground (GND) information on the receiving circuit side by a cable 50. On the receiving circuit side, the ground signal line 24 is grounded (GND) and connected to the connector, and the signal line is connected. The connector of the cable having the signal line 22-2 and the signal line 23 connects to the terminal board 21-4. In this manner, the use / non-use of the driver 30 in the transmission circuit side can be controlled by the ground information on the reception circuit side. If the receiving circuit is not mounted, a use / non-use judging circuit 130 having a function capable of eliminating the need to transmit the signal line 12-2 is provided. It is configured to input to the signal input terminal.
[0051]
That is, the difference between the second and fourth embodiments is that when the respective connectors on the transmission circuit side and the reception circuit side are connected to the cable 50 via the terminal boards 11-4 and 21-4, the receiver 20 is not used. In the same manner as in the second embodiment, the ground signal GND on the transmission circuit side becomes the missing monitoring signal 108, and is input as the control signal 106 to the control signal input terminal of the fourth embodiment. In the case of the mode, the ground signal GND on the receiving circuit side becomes a missing monitoring signal 118, which is input to the control input terminal of the driver 30 as a control signal 116.
[0052]
As a result, similarly to the receiver 20 in the signal transmission circuit according to the second embodiment, the unbalanced vibration 102 of the output of the receiver 20 is output as a valid signal.
[0053]
As described above, in the fourth embodiment, the driver 30 for converting the input unbalanced signal 100 into the balanced signal 101 is provided with the unbalanced-balanced conversion device having the control function capable of controlling the balanced output signal to high impedance. When the receiver 20 is connected to the cable 50 by the disconnection monitoring signal 118 and connected to the transmission circuit side, the signal output is determined to be valid, and the balance signal 101 is output by the control signal 116.
[0054]
Also, when the receiver 20 is not connected to the cable 50 or when the cable 50 is not connected to the terminal board 11-4 on the transmission circuit side, the reception signal becomes invalid and the transmission signal becomes invalid, This signal transmission is determined to be invalid. Accordingly, the resistor 119 is pulled up to Vcc which is the power supply voltage of the driver 30 so that the necessary balanced signal 101 is not output from the driver 30, so that the control function of the driver 30 controls the impedance to a high impedance, and unnecessary signals are transmitted to the cable. By not transmitting the EMI radiation from the EMI, the EMI radiation level can be reduced.
[0055]
In each of the first to fourth embodiments, the circuit including the drivers 10 and 30 on the transmission circuit side and the circuit including the receiver 20 and the current detection circuit 105 on the reception circuit side are each one printed wiring. The terminal boards 11-1 and 21-1 are configured in a board, and each of the terminal boards 11-1 and 21-1 may be considered as a connector into which these printed wiring boards can be inserted and removed, and the cable 50 may be considered to be connected to this connector in advance. In this case, it is possible to consider whether the printed circuit board on the transmission circuit side or the reception circuit side is connected to or disconnected from the cable by inserting and removing the connector. In this case, if the pudding disconnects from the connector, the signal transmission is determined to be invalid by the disconnection monitoring signals 107, 108, and 118.
[0056]
【The invention's effect】
As described above, the present invention receives an unbalanced signal, converts the unbalanced signal into a balanced signal, and transmits the balanced signal through a pair of signal lines, and transmits a balanced signal from the pair of signal lines. And a receiving circuit that terminates a balanced signal from the cable, converts the converted signal into an unbalanced signal, and outputs the unbalanced signal, and monitors whether a pair of signal lines on the transmitting circuit side are connected to the cable. A signal is transmitted from the receiving circuit side to the transmitting circuit side via the cable monitoring signal line, and when a connection with the cable is detected, a control signal based on the detection result allows the receiving circuit to transmit an unbalanced signal. Providing the monitoring means has the following effects.
[0057]
First, since the transmission circuit monitors the connection to the cable, it is possible to determine whether the output of the reception circuit is valid or invalid and to transmit a signal.
[0058]
Second, there is an effect that the output of the receiving circuit can be prevented from becoming unstable when the transmitting circuit is not connected to the cable or when the cable is opened.
[0059]
Third, by monitoring the connection with the receiving circuit, there is an effect that unnecessary signals are not transmitted from the cable, thereby reducing the EMI radiation level.
[0060]
Fourth, an LVDS device that realizes high-speed signal transmission. When transmitting a low-amplitude differential balanced signal for transmitting a signal at a higher speed, high-speed signal transmission with the first to third effects becomes possible. This has the effect of preventing the output of the receiving circuit from becoming unstable.
[0061]
Fifth, the adoption of a device that transmits a low-amplitude differential signal (LVDS) to the transmission circuit and the reception circuit has the effect of reducing power consumption and reducing unnecessary wave noise radiation levels.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a signal transmission circuit according to a first embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration of a signal transmission circuit according to a second embodiment of the present invention.
FIG. 3 is a block diagram illustrating a configuration of a signal transmission circuit according to a third embodiment of the present invention.
FIG. 4 is a block diagram illustrating a configuration of a signal transmission circuit according to a fourth embodiment of the present invention.
[Explanation of symbols]
10, 30 Driver 20 Receiver 11-1, 11-2, 11-3, 11-4, 21-1, 21-2, 21-3, 21-4 Terminal board 50 Cable 103 Termination resistance 104, 109, 119 Resistance 100, 102 Unbalanced signal 101 Balanced signal 105 Current loop detection circuit 106, 116 Control signal 107, 108, 118 Missing monitoring signal 130 Use / unused determination circuit

Claims

A transmission circuit that receives the unbalanced signal, converts the unbalanced signal into a balanced signal, and sends the balanced signal through a pair of signal lines; a cable that transmits the balanced signal from the pair of signal lines; A receiving circuit that terminates the balanced signal from the cable and converts the signal into the unbalanced signal and outputs the signal.
A monitoring signal for monitoring whether the pair of signal lines on the transmitting circuit side is connected to the cable is connected to the transmitting circuit side and the receiving circuit side via a monitoring signal line of the cable to generate a monitoring signal. A signal transmission circuit comprising connection monitoring means for transmitting and detecting the signal, and enabling the receiving circuit to transmit the unbalanced signal by a control signal based on the detection result.

The connection monitoring means sends a current of the monitoring signal for monitoring the connection to the receiving circuit side to the pair of monitoring signal lines of the cable and returns a current of the monitoring signal from the transmission circuit. When detecting the monitoring current loop detection circuit that sends out the control signal, and on the transmission circuit side, when the pair of signal lines that send out the balanced signal is connected to the cable that transmits the balanced signal, The signal transmission circuit according to claim 1, further comprising: a short-circuit line connected to the pair of monitoring signal lines in the cable and short-circuited in the transmission circuit.

The connection monitoring means, when the pair of signal lines for transmitting the balanced signal is connected to the cable for transmitting the balanced signal, between the transmitting circuit side and the receiving circuit side, A first ground line connected to the monitoring signal line in the transmission circuit and grounded in the transmission circuit; and a first ground line connected to the grounded first monitoring signal line of the cable in the reception circuit in the first circuit. 2. The signal transmission circuit according to claim 1, further comprising a first control signal for transmitting the signal line to the reception circuit.

The connection monitoring means, when the pair of signal lines for transmitting the balanced signal is connected to the cable for transmitting the balanced signal, between the transmitting circuit side and the receiving circuit side, A first ground line connected to the monitor signal line in the transmission circuit and grounded in the transmission circuit; and a first grounded first monitor signal line of the cable in the reception circuit connected to the first monitor signal line. A first control signal for sending the ground first signal line to the receiving circuit, a second ground line for grounding in the receiving circuit, and a second grounding of the cable in the receiving circuit 2. The signal according to claim 1, wherein the signal is connected to the second monitoring signal line, and the second signal line is transmitted to the transmission circuit, and the balanced signal can be transmitted by a second control signal. Transmission circuit.

A transmission circuit that receives the unbalanced signal, converts the unbalanced signal into a balanced signal, and sends the balanced signal through a pair of signal lines; a cable that transmits the balanced signal from the pair of signal lines; A receiving circuit that terminates the balanced signal of the above and converts the signal into the unbalanced signal and outputs the signal.
On the receiving circuit side, the pair of signal lines on the transmitting circuit side is connected or not connected to the cable, or artificially based on information on whether the pair of signal lines is used or unused. A signal transmission circuit, comprising setting means for setting transmission of a control signal, and determining whether the transmission signal of the receiving circuit is valid or invalid according to the presence or absence of the input of the control signal.

6. The signal transmission circuit according to claim 5, wherein said setting means includes a timer capable of presetting a time zone in which said pair of signal lines on said transmission circuit side are connected to said cable and said control signal is transmitted. .

6. The device according to claim 1, wherein the receiving circuit comprises a balanced-to-unbalanced conversion Low Voltage Differential Signaling device having a control signal input terminal for enabling input of the control signal. 7. The signal transmission circuit according to claim 6,

5. The device according to claim 1, wherein the transmission circuit is configured by an unbalanced-balanced conversion Low Voltage Differential Signaling device with a control signal input terminal that enables input of the second control signal. , 5 and 6.