JP4327279B2

JP4327279B2 - Bidirectional CATV system relay amplifier

Info

Publication number: JP4327279B2
Application number: JP32223598A
Authority: JP
Inventors: 晴彦稲吉
Original assignee: Maspro Denkoh Corp
Current assignee: Maspro Denkoh Corp
Priority date: 1998-11-12
Filing date: 1998-11-12
Publication date: 2009-09-09
Anticipated expiration: 2018-11-12
Also published as: JP2000151477A

Description

【０００１】
【発明の属する技術分野】
本発明は、センタ装置から端末側に至る信号伝送用の伝送線上に設けられて、この伝送線を双方向に流れる信号を各々増幅する双方向ＣＡＴＶシステムの中継増幅器に関する。
【０００２】
【従来の技術】
従来より、双方向ＣＡＴＶシステムにおいて、センタ装置に接続された幹線や幹線から分岐した分岐線に設けられて、これらの伝送線を双方向に流れる信号を各々増幅する中継増幅器（具体的には、幹線増幅器，幹線分岐増幅器，幹線から分岐した分岐線に設けられる中継増幅器や分岐増幅器等）には、センタ装置から端末側に伝送される下り信号を増幅する下り信号増幅回路と、端末側からセンタ装置側に伝送される上り信号を増幅する上り信号増幅回路とが内蔵されている。
【０００３】
また最近では、端末側からセンタ装置側に伝送可能な情報量を多くするために、上り信号の伝送周波数帯として、下り信号の周波数帯（例えば、７０ＭＨｚ〜５５０ＭＨｚ帯）よりも低い従来の周波数帯（例えば、１０ＭＨｚ〜５５ＭＨｚ帯）だけでなく、下り信号の周波数帯よりも高い周波数帯（例えば、６５０ＭＨｚ〜７７０ＭＨｚ帯）をも設定し、これら各伝送周波数帯を使って、より多くの上り信号を伝送できるようにした双方向ＣＡＴＶシステムも提案されている。
【０００４】
そして、この種のシステムにおいて使用される中継増幅器では、各周波数帯の上り信号を増幅する必要があるため、例えば、特開平３−４２９１９号公報に記載のように、端末側伝送線に接続される中継増幅器の出力端子側にて、端末側から伝送されてきた上り信号を、低周波数帯の上り信号（以下、上りＬ信号という）と、高周波数帯の上り信号（以下、上りＨ信号という）とに分波し、その分波後の各上り信号（上りＬ信号及び上りＨ信号）を夫々専用の増幅回路にて増幅し、更に、センタ装置側伝送線に接続される中継増幅器の入力端子側にて、増幅後の各上り信号を混合して、センタ装置側伝送線に出力するようにしている。
【０００５】
【発明が解決しようとする課題】
しかし、このように構成された中継増幅器では、上りＬ信号と上りＨ信号とを夫々専用の増幅回路にて増幅することから、下り信号増幅用の増幅回路を含めると、中継増幅器には３種類の増幅回路を設けなければならず、中継増幅器のコストアップを招くという問題があった。
【０００６】
また、これら３種類の増幅回路は、夫々、対応する信号を所定レベルまで増幅する必要があるため、中継増幅器全体の消費電力が増加し、特に、何台もの中継増幅器を使用する大規模ＣＡＴＶシステムでは、省エネ化の妨げになるという問題もある。
【０００７】
また、中継増幅器の消費電力が大きくなるということは、発熱量も大きくなることから、ヒートシンクや放熱ファン等、中継増幅器に収納する発熱対策用の部品も大きくなり、中継増幅器の大型化を招くという問題もある。
本発明は、こうした問題に鑑みなされたものであり、双方向ＣＡＴＶシステムの伝送線を流れる下り信号，上りＬ信号及び上りＨ信号を夫々増幅する中継増幅器において、これら各信号を増幅する増幅回路の構成を簡単にし、中継増幅器の小型化及び省エネ化を図ることを目的とする。
【０００８】
【課題を解決するための手段及び発明の効果】
かかる目的を達成するためになされた本発明（請求項１、２に記載）の双方向ＣＡＴＶシステムの中継増幅器においては、センタ装置側より伝送線を介して入力される下り信号が、第１フィルタ回路が設けられた下り信号入力経路を介して、下り信号増幅回路に入力される。すると、下り信号増幅回路は、その入力された下り信号を増幅し、端末側に出力する。また、この下り信号増幅回路から出力された、増幅後の下り信号は、第１フィルタ回路が設けられた下り信号出力経路を介して、端末側伝送線上に出力される。
【０００９】
また、中継増幅器が設けられる伝送線には、端末側からセンタ装置側への上り信号として、下り信号よりも低い周波数帯の上りＬ信号と、下り信号よりも高い周波数帯の上りＨ信号との２種類の上り信号が流れるが、本発明の中継増幅器では、このように端末側より伝送されてくる２種類の上り信号（上りＬ信号，上りＨ信号）の内、周波数が高い上りＨ信号は、第２フィルタ回路が設けられた上り信号入力経路を介して上り信号増幅回路に入力され、周波数が低い上りＬ信号は、第３フィルタ回路が設けられた上り信号入力経路を介して上り信号増幅回路に入力される。この結果、上り信号増幅回路には、これら各上り信号が混合して入力され、上り信号増幅回路は、各上り信号を同時に増幅する。
【００１０】
そして、この上り信号増幅回路による増幅後の上り信号の内、上りＨ信号は、第２フィルタ回路が設けられた上り信号出力経路を介して、センタ装置側伝送線上に出力され、上りＬ信号は、第３フィルタ回路が設けられた上り信号出力経路を介して、センタ装置側伝送線路上に出力される。
【００１１】
このように、本発明の中継増幅器においては、上りＨ信号及び上りＬ信号を夫々増幅するために、専用の増幅回路を設けるのではなく、これら各信号を混合した上り信号を増幅する、各上り信号共通の上り信号増幅回路を設け、この上り信号増幅回路にて、上りＨ信号及び上りＬ信号を同時に増幅するようにしている。
【００１３】
ところで、双方向ＣＡＴＶシステムの中継増幅器は、下り・上りの各信号が伝送線（幹線や分岐線）を通過する際に生じる減衰量を補うために、その伝送線の途中で各信号をその減衰量に見合った分だけ増幅するものであることから、上記各増幅回路の増幅特性は、各信号の伝送線上での減衰特性に対応して、周波数が高いほど利得が大きくなるように、周波数に対して傾斜した所謂チルト特性に設定する必要がある。
【００１４】
そして、本発明の中継増幅器では、周波数が高い上りＨ信号と周波数が低い上りＬ信号とを共通の上り信号増幅回路にて増幅するが、これら両上り信号を一つの増幅回路だけで増幅するには、その増幅特性を極めて広い周波数範囲（例えば、既述したように上りＨ信号が６５０ＭＨｚ〜７７０ＭＨｚで、下りＬ信号が１０ＭＨｚ〜５５ＭＨｚである場合には、１０ＭＨｚ〜７７０ＭＨｚの周波数範囲内）で、適正なチルト特性にしなければならない。しかし、現実問題として、こうした広い周波数範囲で、増幅回路の増幅特性を周波数に対して一定の傾きで変化するチルト特性にすることは難しく、特に、上りＨ信号側の高い周波数領域で利得を確保するのは難しい。
【００１５】
そこで、本発明では、２系統の上り信号入力経路及び上り信号出力経路の内、第２フィルタ回路が設けられる上り信号入力経路及び上り信号出力経路の一方にだけ、上りＨ信号を増幅する補助増幅回路を設けている。
【００１６】
従って、本発明の中継増幅器によれば、補助増幅回路と上り信号増幅回路とで上りＨ信号を増幅することができ、上り信号増幅回路単体で上りＨ信号を増幅するのに必要な利得が得られない場合であっても、上りＨ信号を所望のレベルまで増幅することができる。
【００１７】
このように、本発明では、上り信号増幅用の増幅回路として、上り信号増幅回路と補助増幅回路との２種類の増幅回路を使用する。しかし、補助増幅回路は、上り信号増幅回路にて上りＨ信号を増幅できない分を増幅すればよいので、上りＨ信号増幅用の増幅回路を単体で用いる場合に比べて、その利得を小さくし、消費電力を抑制できる。また上り信号増幅回路の利得も小さくすることができ、その消費電力を抑制できる。
よって、本発明の中継増幅器によれば、上りＨ信号と上りＬ信号とを夫々専用の増幅回路を用いて増幅する従来装置に比べ、消費電力を抑制して、省エネ化を図ることができる。また、消費電力の低減に伴い、中継増幅器での発熱量を抑制することができ、延いては、発熱対策用部品（ヒートシンクや放熱ファン等）を小型にして、中継増幅器の小型・軽量化を図ることができる。
【００１８】
また、本発明（請求項１、２）の中継増幅器の内、特に、請求項１に記載の中継増幅器においては、２系統の上り信号入力経路に、それぞれ、当該中継増幅器による上りＨ信号及び上りＬ信号の増幅特性が、周波数が高いほど利得が大きいチルト特性となるよう、上りＨ信号及び上りＬ信号をレベル調整するイコライザが設けられている。そして、補助増幅回路は、第２フィルタ回路が設けられる上り信号入力経路に、イコライザと直列になるよう接続されている。
【００１９】
このため、請求項１に記載の中継増幅器によれば、イコライザ及び補助増幅回路によって、上り信号の増幅特性を、伝送線で生じる上り信号の減衰特性に対応したチルト特性に設定することができる。
【００２０】
一方、請求項２に記載の中継増幅器においては、２系統の上り信号出力経路に、それぞれ、上りＨ信号及び上りＬ信号を、伝送線での各上り信号の減衰特性に合わせて減衰させる出力レベル調整部が設けられており、補助増幅回路は、第２フィルタ回路が設けられる上り信号出力経路に、出力レベル調整部と直列になるよう接続されている。
【００２１】
このため、請求項２に記載の中継増幅器によれば、センタ装置側伝送線の線路長が設定値よりも短く、この伝送線で生じる下り信号の減衰量が小さい場合に、各上り信号の信号レベルを、その伝送線での各上り信号の減衰特性に合わせて減衰させて、センタ装置側伝送線上に設けられた前段の伝送機器（或いはセンタ装置）への上り信号の入力レベルを、一定レベルにすることができる。
【００２３】
【発明の実施の形態】
以下に本発明の実施例を図面と共に説明する。
図１は、本発明が適用された実施例の中継増幅器の概略構成を表すブロック図である。
【００２４】
本実施例の中継増幅器は、センタ装置から端末側に、所定周波数帯（例えば、７０ＭＨｚ〜５５０ＭＨｚ帯）の下り信号（図１に点線矢印で示す）を伝送し、端末側からセンタ装置側には、下り信号よりも周波数の低い所定周波数帯（例えば、１０ＭＨｚ〜５５ＭＨｚ帯）の上りＬ信号（図１に実線矢印で示す）と、下り信号よりも周波数の高い所定周波数帯（例えば、６５０ＭＨｚ〜７７０ＭＨｚ帯）の上りＨ信号（図１に一点鎖線矢印で示す）とを伝送するように構成された双方向ＣＡＴＶシステムにおいて、これら各信号を幹線や分岐線等の伝送線上で双方向に増幅するのに使用されるものである。
【００２５】
そして、この中継増幅器は、図１に示すように、センタ装置側伝送線に接続される入力端子Ｔinと、カットオフ周波数７０ＭＨｚのハイパスフィルタ（以下、ＨＰＦと記載する）１２と、カットオフ周波数５５０ＭＨｚのローパスフィルタ（以下、ＬＰＦと記載する）１４とからなる下り信号入力経路を介して、センタ装置側から伝送されてきた下り信号を取り込み、その取り込んだ下り信号の信号レベルを、入力レベル調整部１６にて所定レベルに調整した後、下り信号増幅回路１８にて増幅し、その増幅後の下り信号を、カットオフ周波数５５０ＭＨｚのＬＰＦ２０と、カットオフ周波数７０ＭＨｚのＨＰＦ２２と、端末側伝送線に接続される出力端子Ｔout とからなる下り信号出力経路を介して、端末側伝送線上に出力するよう構成されている。
【００２６】
ここで、入力レベル調整部１６は、入力端子Ｔinに接続されるセンタ装置側伝送線の線路長が設定値よりも短く、この伝送線で生じる下り信号の減衰量が小さい場合に、下り信号を、伝送線での下り信号の減衰特性に合わせて、設定レベルまで減衰させることにより、下り信号増幅回路１８への下り信号の入力レベルを予め設定された一定レベルに調整するためのもの（擬似線路；所謂ＢＯＮ回路）である。
【００２７】
また、下り信号増幅回路１８は、端末側伝送線が所定の長さであると仮定して設定した減衰特性に対応する増幅特性（チルト特性）で下り信号を増幅するためのものであり、前後二段の増幅回路１８ａ，１８ｂと、その間に設けられて、下り信号増幅回路１８の増幅特性が所望のチルト特性となるように下り信号をレベル調整するイコライザ１８ｃとから構成されている。
【００２８】
また、下り信号入力経路を構成するＨＰＦ１２及びＬＰＦ１４、下り信号出力経路を構成するＬＰＦ２０及びＨＰＦ２２は、夫々、これら各経路を通過する信号を、下り信号の周波数帯（７０ＭＨｚ〜５５０ＭＨｚ）の信号成分に規制するバンドパスフィルタを構成しており、請求項１記載の第１フィルタ回路として機能する。
【００２９】
次に、中継増幅器には、上記各上り信号を増幅するために、上りＬ信号から上りＨ信号までの周波数帯域（１０ＭＨｚ〜７７０ＭＨｚ）で所定の増幅特性を有する上り信号増幅回路２４が備えられる。
そして、端末側から伝送されてきた上りＨ信号は、出力端子Ｔout と、ＨＰＦ２２と、カットオフ周波数６５０ＭＨｚのＨＰＦ２６と、同じくカットオフ周波数６５０ＭＨｚのＨＰＦ２８とからなる上りＨ信号入力経路を介して、上り信号増幅回路２４に入力される。また、端末側から伝送されてきた上りＬ信号は、出力端子Ｔout と、カットオフ周波数５５ＭＨｚのＬＰＦ３０と、同じくカットオフ周波数５５ＭＨｚのＬＰＦ３２とからなる上りＬ信号入力経路を介して、上り信号増幅回路２４に入力される。
【００３０】
この結果、上り信号増幅回路２４には、ＨＰＦ２８及びＬＰＦ３２を介して、上りＨ信号と上りＬ信号とを混合した上り信号が入力され、上り信号増幅回路２４は、これら各信号を所定レベルまで増幅して出力することになる。
また、上りＨ信号入力経路を構成するＨＰＦ２６とＨＰＦ２８との間には、上りＨ信号を所定レベルまで増幅する補助増幅回路３４、及び、補助増幅回路３４と上り信号増幅回路２４とによる上りＨ信号の増幅特性が所定のチルト特性（図２参照）となるように、上りＨ信号をレベル調整するイコライザ３６が設けられている。また、上りＬ信号入力経路を構成するＬＰＦ３０とＬＰＦ３２との間には、上り信号増幅回路２４による上りＬ信号の増幅特性が所定のチルト特性（図２参照）となるように、上りＬ信号をレベル調整するイコライザ３８が設けられている。
【００３１】
そして、上り信号増幅回路２４により増幅された上り信号の内、上りＨ信号は、カットオフ周波数６５０ＭＨｚのＨＰＦ４０と、上りＨ信号の出力レベルを調整する出力レベル調整部４２と、カットオフ周波数６５０ＭＨｚのＨＰＦ４４と、上述のＨＰＦ１２と、入力端子Ｔinとからなる上りＨ信号出力経路を介して、センタ装置側伝送線上に出力される。また、上りＬ信号は、カットオフ周波数５５ＭＨｚのＬＰＦ４６と、上りＬ信号の出力レベルを調整する出力レベル調整部４８と、カットオフ周波数５５ＭＨｚのＬＰＦ５０と、入力端子Ｔinとからなる上りＬ信号出力経路を介して、センタ装置側伝送線上に出力される。
【００３２】
尚、出力レベル調整部４２，４８は、夫々、入力端子Ｔinに接続されるセンタ装置側伝送線の線路長が設定値よりも短く、この伝送線で生じる下り信号の減衰量が小さい場合に、各上り信号の信号レベルを、伝送線での各上り信号の減衰特性に合わせて減衰させることにより、センタ装置側伝送線上に設けられた前段の伝送機器（或いはセンタ装置）への上り信号の入力レベルを、予め設定された一定レベルにするためのもの（擬似線路；所謂ＢＯＮ回路）である。
【００３３】
従って、入力端子Ｔinからセンタ装置側伝送線上には、図２に示すように、その伝送線での減衰特性に対応して各上り信号を増幅した上り信号が出力されることになり、センタ装置側伝送線に設けられた前段の伝送機器（或いはセンタ装置）には、各上り信号が一定レベルで入力されることになる。
【００３４】
尚、図２は、入力端子Ｔinが接続されたセンタ装置側伝送線の線路長が設計時に設定された所定長さであるとき（換言すれば出力レベル調整部４２，４８を動作させないとき）に、入力端子Ｔinからセンタ装置側伝送線に出力する各上り信号の具体例を表しており、中継増幅器は、例えば、入力端子Ｔinから出力する上りＬ信号が、１０ＭＨｚで８７．６ｄＢμ、５５ＭＨｚで９８．７ｄＢμとなり、上りＨ信号が、６５０ＭＨｚで９４．５ｄＢμ、７７０ＭＨｚで９５．８ｄＢμとなるように、各上り信号を増幅する。
【００３５】
ここで、上りＨ信号入力経路上のＨＰＦ２２，２６，２８、及び、上りＨ信号出力経路上のＨＰＦ４０，４４，１２は、当該中継増幅器が設けられる伝送線上を流れる信号の内、上りＨ信号のみを選択的に通過させるためのものであり、請求項１記載の第２フィルタ回路に相当する。また、上りＬ信号入力経路上のＬＰＦ３０，３２、及び、上りＬ信号出力経路上のＬＰＦ４６，５０は、当該中継増幅器が設けられる伝送線上を流れる信号の内、上りＬ信号のみを選択的に通過させるためのものであり、請求項１記載の第３フィルタ回路に相当する。
【００３６】
また、本実施例の中継増幅器においては、入力端子ＴinとＨＰＦ１２，ＬＰＦ５０との間、及び、出力端子Ｔout とＨＰＦ２２，ＬＰＦ３０との間に、夫々、当該中継増幅器が設けられる伝送線に落雷等によって誘起される高電圧から内部回路を保護するための耐雷フィルタ５２，５４が設けられている。
【００３７】
以上説明したように、本実施例の中継増幅器においては、端末側から伝送されてきた上りＨ信号を、ＨＰＦ２２及びＨＰＦ２６を介して補助増幅回路３４に入力することにより、上りＨ信号を補助増幅回路３４にて所定レベルまで増幅した後、イコライザ３６，ＨＰＦ２８を介して、上り信号増幅回路２４に入力すると共に、端末側から伝送されてきた上りＬ信号を、ＬＰＦ２２，イコライザ３８，ＬＰＦ３２を介して、上り信号増幅回路２４に入力し、上り信号増幅回路２４にて、上りＨ信号と上りＬ信号とを同時に増幅するようにされている。
【００３８】
このため、本実施例の中継増幅器によれば、上りＨ信号と上りＬ信号とを夫々専用の増幅回路を用いて増幅する従来装置に比べて、上り信号増幅用の回路構成を簡単にし、消費電力を低減できる。従って、本実施例の中継増幅器を用いて双方向ＣＡＴＶシステムを構築すれば、システム全体で省エネ化を図ることができる。また、消費電力の低減に伴い、中継増幅器での発熱量も抑制できることから、中継増幅器の発熱対策のために設ける発熱対策用部品（ヒートシンクや放熱ファン等）を小型にすることができ、これによっても、中継増幅器の小型・軽量化を図ることができる。
【００３９】
また、本実施例では、上りＨ信号を所望レベルまで増幅するために、上りＨ信号を、一旦、補助増幅回路３４にて増幅した後、上り信号増幅回路２４に入力するよう構成されていることから、上りＨ信号と上りＬ信号とを上り信号増幅回路２４だけで増幅するようにした場合に比べて、上り信号増幅回路２４の利得を小さくすることができる。
【００４０】
つまり、上り信号増幅回路２４だけで、図２に示したチルト特性の上り信号を得るには、上り信号増幅回路２４の利得を、上りＨ信号を最大周波数（７７０ＭＨｚ）で９５．８ｄＢμまで増幅できるように設定しなければならず、このためには、上り信号増幅回路２４を構成する増幅素子（トランジスタ）の数を増やしたり、各増幅素子に増幅率の大きな高価なトランジスタを使用しなければならなくなる。
【００４１】
しかし、本実施例では、上りＨ信号を補助増幅回路３４にて増幅するようにしていることから、例えば、上り信号増幅回路２４の利得を、上りＬ信号を最大周波数（５５ＭＨｚ）で８９．７ｄＢμまで増幅できる程度に設定し、上りＬ信号を所望レベルまで増幅するのに必要な利得の不足分を、補助増幅回路３４で補うようにすることができる。
【００４２】
従って、本実施例によれば、上りＬ信号と上りＨ信号とを上り信号増幅回路２４だけで増幅するようにした場合に比べて、上り信号増幅回路２４の利得を小さくすることができる。よって、本実施例によれば、上り信号増幅回路２４の構成を簡単にして、より安価に実現することができると共に、上り信号増幅回路２４の利得を小さくすることにより、消費電力を抑え、発熱量も小さくできる。
【００４３】
以上、本発明の一実施例について説明したが、本発明は、上記実施例に限定されるものではなく、種々の態様を採ることができる。
例えば、上記実施例では、端末側から伝送されてきた上りＨ信号を補助増幅回路３４にて増幅した後、その増幅後の上りＨ信号と端末側から伝送されてきた上りＬ信号とを、共通の上り信号増幅回路２４にて増幅し、センタ装置側から伝送されてきた下り信号は、下り信号増幅回路１８にて増幅するものとして説明したが、センタ装置及び端末側から、周囲温度等の使用環境変化によって生じる伝送線の減衰特性の変化に伴う各伝送信号のレベル変動を防止するためのパイロット信号（利得調整用信号）が伝送されてくる双方向ＣＡＴＶシステムであれば、図３に示す如く、下り信号増幅回路１８及び上り信号増幅回路２４に対して、夫々、下り信号及び上り信号の出力レベルを調整する利得調整回路６４，７４を設けるようにすればよい。
【００４４】
即ち、図３に示す中継増幅器は、図１に示した中継増幅器に対して、更に、
(1) 下り信号増幅回路１８から出力される下り信号の一部を分岐する分岐回路６２。
(2) 下り信号増幅回路１８内の前段の増幅回路１８ａと後段の増幅回路１８ｂとの間に設けられ、下り信号増幅回路１８からの下り信号の出力レベルの傾斜特性を微調整するための減衰器６６。
【００４５】
(3) 分岐回路６２にて分岐された下り信号の中から、センタ装置側より送信されてきた下り利得調整用のパイロット信号を抽出して、その信号レベルが予め設定された設定レベルとなるように減衰器６６の減衰量を調整することにより、下り信号増幅回路１８全体の利得を調整する利得調整回路６４。
【００４６】
(4) ＨＰＦ４０から出力レベル調整部４２に至る上りＨ信号出力経路に設けられて、上り信号増幅回路２４から出力された上りＨ信号の一部を分岐する分岐回路７２。
(5) ＨＰＦ２８及びＬＰＦ３２から上り信号増幅回路２４に至る、各上り信号共通の入力経路に設けられて、上り信号増幅回路２４からの上り信号（詳しくは上りＨ信号及び上りＬ信号）の出力レベルの傾斜特性を微調整するための減衰器７６。
【００４７】
(6) 分岐回路７２にて分岐された上りＨ信号の中から、端末側より送信されてきた上り利得調整用のパイロット信号を抽出して、その信号レベルが予め設定された設定レベルとなるように減衰器７６の減衰量を調整することにより、下り信号増幅回路２４の利得を調整する利得調整回路７４。
【００４８】
を設けたものであり、他の構成は図１に示した中継増幅器と全く同様であり、上記実施例と同様に動作する。
そして、下り利得調整用の減衰器６６は、下り信号増幅回路１８の利得が適正値にあるとき、下り信号の全周波数領域で一定の減衰量（基準減衰量）となるように設定されており、利得調整回路６４が下り信号増幅回路１８の利得を上げるために減衰量を減少させる指令を出力すると、基準減衰量に対して周波数が高い程減衰量が大きく低下し、利得調整回路６４が下り信号増幅回路１８の利得を下げるために減衰量を増加させる指令を出力すると、基準減衰量に対して周波数が高い程減衰量が大きく増加するようにされている。
【００４９】
また、上り利得調整用の減衰器７６は、上り信号増幅回路２４の利得が適正値にあるとき、上りＬ信号から上りＨ信号までの全周波数領域で一定の減衰量（基準減衰量）となるように設定されており、利得調整回路７４が上り信号増幅回路２４の利得を上げるために減衰量を減少させる指令を出力すると、基準減衰量に対して周波数が高い程減衰量が大きく低下し、利得調整回路７４が上り信号増幅回路２６の利得を下げるために減衰量を増加させる指令を出力すると、基準減衰量に対して周波数が高い程減衰量が大きく増加するようにされている（図４参照）。
【００５０】
尚、これは、伝送線の温度変化に伴に伴う伝送線での減衰量の増減特性に対応して、各増幅回路１８，２４の利得を調整するためである。
このように構成された図３の中継増幅器においては、利得調整回路６４及び７４が、夫々、センタ装置及び端末側より伝送されてきたパイロット信号に基づき、減衰器６６及び７６の減衰特性を調整することにより、下り信号増幅回路１８及び上り信号増幅回路２４の利得を調整し、各増幅回路１８及び２４からの信号の出力レベルを最適レベルに設定することから、下り信号を伝送してくるセンタ装置側伝送線や上り信号を伝送してくる端末側伝送線の減衰特性が温度等の使用環境によって変化しても、各信号を最適レベルで出力することが可能になる。
【００５１】
また上りＬ信号と上りＨ信号は、各信号共通の上り信号増幅器２４の利得調整を行うだけで最適レベルに設定され、これら各上り信号のレベル調整のために、専用の利得調整回路を設ける必要がないため、各上り信号を専用の増幅回路で増幅するようにした従来装置に比べて、利得調整用の回路を簡素化することができ、中継増幅器の小型化及びコスト低減を図ることができる。
【００５２】
一方、上記実施例では、本発明を、双方向ＣＡＴＶシステムの幹線や分岐線に流れる各信号を単に増幅するだけの中継増幅器に適用した場合について説明したが、本発明は、上記構成に加えて、下り信号増幅回路１８により増幅された下り信号を下位の伝送線（分岐線）に分岐させる分岐回路と、その分岐線を介して端末側から伝送されてきた各上り信号を、出力端子Ｔout から入力された各上り信号と混合させて、上りＨ信号入力経路及び上りＬ信号入力経路に入力する混合回路とを備えた中継増幅器（所謂分岐増幅器）に適用することもできる。そして、このような中継増幅器（分岐増幅器）においても、上記実施例と同様の効果を得ることができる。
【００５３】
また例えば、上記実施例では、上りＨ信号を補助的に増幅する補助増幅回路３４を、上りＨ信号入力経路に設け、補助増幅回路３４により増幅した上りＨ信号を上り信号増幅回路２４に入力するものとして説明したが、例えば、補助増幅回路３４を上りＨ信号出力経路（より具体的には、ＨＰＦ４０と出力レベル調整部４２との間）に設け、上り信号増幅回路２４から出力される上りＨ信号を補助増幅回路３４にて増幅するようにしてもよい。
【図面の簡単な説明】
【図１】実施例の双方向ＣＡＴＶシステム用の中継増幅器の構成を表すブロック図である。
【図２】中継増幅器の入力端子Ｔinからセンタ装置側に出力される上り信号を表す説明図である。
【図３】利得調整回路を備えた双方向ＣＡＴＶシステム用の中継増幅器の構成を表すブロック図である。
【図４】図３に示す利得調整用の減衰器の減衰特性を説明する説明図である。
【符号の説明】
１６…入力レベル調整部、１８…下り信号増幅回路、２４…上り信号増幅回路、３４…補助増幅回路、１８ｃ，３６，３８…イコライザ、４２，４８…出力レベル調整部、５２，５４…耐雷フィルタ、１２，２２，２６，２８，４０，４４…ＨＰＦ（ハイパスフィルタ）、１４，２０，３０，３２，４６，５０…ＬＰＦ（ローパスフィルタ）、Ｔin…入力端子、Ｔout …出力端子、６２，７２…分岐回路、６４，７４…利得調整回路、６６，７６…減衰器。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a relay amplifier for a bidirectional CATV system, which is provided on a transmission line for signal transmission from a center device to a terminal side and amplifies signals flowing in both directions on the transmission line.
[0002]
[Prior art]
Conventionally, in a bidirectional CATV system, a trunk amplifier connected to a center device or a branch line branched from the trunk line, and a relay amplifier (specifically, amplifying each of the signals flowing bidirectionally through these transmission lines) A trunk amplifier, a trunk branch amplifier, a relay amplifier and a branch amplifier provided on a branch line branched from the trunk line), a downlink signal amplifier circuit for amplifying a downlink signal transmitted from the center apparatus to the terminal side, and a center from the terminal side An upstream signal amplifying circuit for amplifying the upstream signal transmitted to the device side is incorporated.
[0003]
Recently, in order to increase the amount of information that can be transmitted from the terminal side to the center device side, the conventional frequency band lower than the frequency band of the downstream signal (for example, 70 MHz to 550 MHz) as the transmission frequency band of the upstream signal. (For example, 10 MHz to 55 MHz band) as well as a frequency band higher than the downlink signal frequency band (for example, 650 MHz to 770 MHz band) is set, and using each of these transmission frequency bands, more upstream signals are transmitted. A bidirectional CATV system that enables transmission is also proposed.
[0004]
In the relay amplifier used in this type of system, it is necessary to amplify the upstream signal in each frequency band. For example, as described in JP-A-3-42919, it is connected to the terminal side transmission line. On the output terminal side of the relay amplifier, the upstream signal transmitted from the terminal side is divided into a low frequency band upstream signal (hereinafter referred to as upstream L signal) and a high frequency band upstream signal (hereinafter referred to as upstream H signal). ), And each upstream signal (upstream L signal and upstream H signal) after the separation is amplified by a dedicated amplifier circuit, and further input to a relay amplifier connected to the transmission line on the center device side On the terminal side, the amplified upstream signals are mixed and output to the center apparatus side transmission line.
[0005]
[Problems to be solved by the invention]
However, in the relay amplifier configured as described above, the upstream L signal and the upstream H signal are amplified by dedicated amplifier circuits. Therefore, when the amplifier circuit for downstream signal amplification is included, the relay amplifier includes three types. Therefore, there is a problem in that the cost of the relay amplifier is increased.
[0006]
In addition, since these three types of amplifier circuits each need to amplify the corresponding signal to a predetermined level, the power consumption of the entire relay amplifier increases, and in particular, a large-scale CATV system using a number of relay amplifiers. Then, there is a problem that it becomes an obstacle to energy saving.
[0007]
In addition, since the power consumption of the relay amplifier increases, the amount of heat generated also increases, so heat sinks, heat dissipation fans, and other parts for heat generation stored in the relay amplifier also increase, leading to an increase in the size of the relay amplifier. There is also a problem.
The present invention has been made in view of such problems, and in a relay amplifier that amplifies a downstream signal, an upstream L signal, and an upstream H signal flowing through a transmission line of a bidirectional CATV system, an amplifier circuit that amplifies each of these signals is provided. The purpose is to simplify the configuration and to reduce the size and energy of the relay amplifier.
[0008]
[Means for Solving the Problems and Effects of the Invention]
  Made to achieve this goalThe present invention (described in claims 1 and 2)In the relay amplifier of the bidirectional CATV system, the downstream signal input from the center device side via the transmission line is input to the downstream signal amplifier circuit via the downstream signal input path provided with the first filter circuit. The Then, the downlink signal amplifier circuit amplifies the input downlink signal and outputs it to the terminal side. Further, the amplified downlink signal output from the downlink signal amplifier circuit is output on the terminal side transmission line via the downlink signal output path provided with the first filter circuit.
[0009]
The transmission line provided with the relay amplifier includes an upstream L signal in a frequency band lower than the downstream signal and an upstream H signal in a frequency band higher than the downstream signal as upstream signals from the terminal side to the center apparatus side. Although two types of upstream signals flow, in the relay amplifier of the present invention, among the two types of upstream signals (upstream L signal and upstream H signal) transmitted from the terminal side in this way, an upstream H signal having a high frequency is The upstream L signal having a low frequency is input to the upstream signal amplifier circuit via the upstream signal input path provided with the second filter circuit, and the upstream signal amplification is performed via the upstream signal input path provided with the third filter circuit. Input to the circuit. As a result, these upstream signals are mixed and input to the upstream signal amplifier circuit, and the upstream signal amplifier circuit simultaneously amplifies the upstream signals.
[0010]
Of the upstream signals amplified by the upstream signal amplifier circuit, the upstream H signal is output on the transmission line on the center device side through the upstream signal output path provided with the second filter circuit, and the upstream L signal is The signal is output onto the transmission line on the center device side through the upstream signal output path provided with the third filter circuit.
[0011]
As described above, in the relay amplifier of the present invention, in order to amplify the upstream H signal and the upstream L signal, a dedicated amplifier circuit is not provided, but each upstream signal obtained by mixing these signals is amplified. An upstream signal amplifier circuit common to the signals is provided, and the upstream signal amplifier circuit simultaneously amplifies the upstream H signal and the upstream L signal.
[0013]
By the way, the relay amplifier of the bidirectional CATV system is adapted to attenuate each signal in the middle of the transmission line in order to compensate for the amount of attenuation that occurs when each downstream / upstream signal passes through the transmission line (trunk line or branch line). The amplification characteristic of each amplification circuit is in accordance with the attenuation characteristic of each signal on the transmission line, so that the gain becomes larger as the frequency is higher. On the other hand, it is necessary to set so-called tilt characteristics that are inclined.
[0014]
In the relay amplifier according to the present invention, the upstream H signal having a high frequency and the upstream L signal having a low frequency are amplified by a common upstream signal amplifier circuit, and these upstream signals are amplified by only one amplifier circuit. Has an amplification characteristic in a very wide frequency range (for example, as described above, when the upstream H signal is 650 MHz to 770 MHz and the downstream L signal is 10 MHz to 55 MHz, within the frequency range of 10 MHz to 770 MHz), It must have proper tilt characteristics. However, as a practical problem, it is difficult to make the amplification characteristic of the amplification circuit change with a constant inclination with respect to the frequency in such a wide frequency range, and in particular, gain is secured in the high frequency region on the upstream H signal side. Difficult to do.
[0015]
  Therefore, in the present invention,Of the two upstream signal input paths and upstream signal output paths,Upstream signal input path provided with the second filter circuitas well asUpstream signal output pathOnly on one side,An auxiliary amplifier circuit is provided to amplify the upstream H signal.ing.
[0016]
Therefore, according to the relay amplifier of the present invention,Even when the auxiliary amplifier circuit and the upstream signal amplifier circuit can amplify the upstream H signal and the gain required to amplify the upstream H signal by the upstream signal amplifier circuit alone cannot be obtained, the upstream H signal Can be amplified to the desired levelit can.
[0017]
Thus, in the present invention,As an amplification circuit for upstream signal amplificationAndTwo types of amplifier circuits, upstream signal amplifier circuit and auxiliary amplifier circuitIs used. But,If the auxiliary amplifier circuit amplifies the amount that the upstream signal amplification circuit cannot amplify the upstream H signal,So goodThe gain can be reduced and the power consumption can be suppressed as compared with the case where the amplifier circuit for amplifying the upstream H signal is used alone. Also, the gain of the upstream signal amplifier circuit can be reduced, and the power consumption can be suppressed.
  Therefore,According to the relay amplifier of the present invention, the upstream H signal and the upstream L signal are amplified using the dedicated amplifier circuits, respectively.Compared to conventional devices, it can reduce power consumption and save energy.it can. Also, along with the reduction in power consumption, the amount of heat generated in the relay amplifier can be suppressed,Heat generation countermeasure parts(Heatsink, heat dissipation fan, etc.)The relay amplifier can be made smaller and lighter.
[0018]
Further, among the relay amplifiers of the present invention (Claims 1 and 2), in particular, Claim 1In the relay amplifier described in the above, the upstream H signal and the upstream L signal amplification characteristics of the upstream amplifier input path of the two systems are respectively set to the upstream H signal so that the higher the frequency, the higher the gain characteristic. An equalizer for adjusting the level of the signal and the upstream L signal is provided. The auxiliary amplifier circuit is connected in series with the equalizer to the upstream signal input path in which the second filter circuit is provided.
[0019]
  For this reason,Claim 1According to the relay amplifier described in (1), the amplification characteristic of the uplink signal can be set to the tilt characteristic corresponding to the attenuation characteristic of the uplink signal generated in the transmission line by the equalizer and the auxiliary amplifier circuit.
[0020]
  On the other hand, claim 2In the relay amplifier described in (2), an output level adjustment unit for attenuating the upstream H signal and the upstream L signal in accordance with the attenuation characteristics of each upstream signal on the transmission line is provided in each of the two upstream signal output paths. The auxiliary amplifier circuit is connected in series with the output level adjustment unit to the upstream signal output path in which the second filter circuit is provided.
[0021]
  For this reason,Claim 2According to the described relay amplifier, when the line length of the transmission line on the center device side is shorter than the set value and the amount of attenuation of the downlink signal generated on this transmission line is small, the signal level of each uplink signal is Thus, the input level of the upstream signal to the upstream transmission device (or the center device) provided on the transmission line on the center device side can be set to a constant level.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of a relay amplifier according to an embodiment to which the present invention is applied.
[0024]
The relay amplifier of this embodiment transmits a downstream signal (indicated by a dotted arrow in FIG. 1) in a predetermined frequency band (for example, 70 MHz to 550 MHz band) from the center device to the terminal side, and from the terminal side to the center device side. , An upstream L signal (indicated by a solid arrow in FIG. 1) having a predetermined frequency band (for example, 10 MHz to 55 MHz band) having a frequency lower than that of the downstream signal, and a predetermined frequency band (for example, 650 MHz to 770 MHz) having a higher frequency than the downstream signal. In a bidirectional CATV system configured to transmit an upstream H signal (indicated by an alternate long and short dash line in FIG. 1), these signals are bidirectionally amplified on a transmission line such as a trunk line or a branch line. Is used.
[0025]
As shown in FIG. 1, the relay amplifier includes an input terminal Tin connected to the transmission line on the center apparatus side, a high-pass filter (hereinafter referred to as HPF) 12 having a cutoff frequency of 70 MHz, and a cutoff frequency of 550 MHz. The downstream signal transmitted from the center apparatus side is taken in via a downstream signal input path composed of a low-pass filter (hereinafter referred to as LPF) 14, and the signal level of the captured downstream signal is set as an input level adjustment unit. 16 is adjusted to a predetermined level, and then amplified by the downstream signal amplification circuit 18, and the downstream signal after the amplification is connected to the LPF 20 having a cutoff frequency of 550 MHz, the HPF 22 having a cutoff frequency of 70 MHz, and the terminal-side transmission line. Output on the terminal-side transmission line via the downstream signal output path composed of the output terminal Tout. There.
[0026]
Here, the input level adjustment unit 16 determines the downlink signal when the line length of the transmission line on the center device side connected to the input terminal Tin is shorter than the set value and the attenuation amount of the downlink signal generated on the transmission line is small. In order to adjust the input level of the downstream signal to the downstream signal amplification circuit 18 to a predetermined constant level by attenuating to the set level in accordance with the attenuation characteristic of the downstream signal on the transmission line (pseudo line) A so-called BON circuit).
[0027]
The downlink signal amplification circuit 18 is for amplifying the downlink signal with an amplification characteristic (tilt characteristic) corresponding to the attenuation characteristic set on the assumption that the terminal-side transmission line has a predetermined length. A two-stage amplifier circuit 18a, 18b, and an equalizer 18c, which is provided between them, and adjusts the level of the downstream signal so that the amplification characteristic of the downstream signal amplifier circuit 18 has a desired tilt characteristic.
[0028]
Further, the HPF 12 and LPF 14 constituting the downstream signal input path, and the LPF 20 and HPF 22 constituting the downstream signal output path, respectively, use the signals passing through these paths as signal components in the downstream signal frequency band (70 MHz to 550 MHz). A band-pass filter to be regulated is configured and functions as a first filter circuit according to claim 1.
[0029]
Next, the relay amplifier is provided with an upstream signal amplification circuit 24 having a predetermined amplification characteristic in a frequency band (10 MHz to 770 MHz) from the upstream L signal to the upstream H signal in order to amplify each upstream signal.
The uplink H signal transmitted from the terminal side is transmitted via an uplink H signal input path including an output terminal Tout, an HPF 22, an HPF 26 having a cutoff frequency of 650 MHz, and an HPF 28 having a cutoff frequency of 650 MHz. The signal is input to the signal amplifier circuit 24. Further, the uplink L signal transmitted from the terminal side is transmitted through an uplink L signal input path including an output terminal Tout, an LPF 30 having a cutoff frequency of 55 MHz, and an LPF 32 having a cutoff frequency of 55 MHz. 24.
[0030]
As a result, the upstream signal amplification circuit 24 receives an upstream signal obtained by mixing the upstream H signal and the upstream L signal via the HPF 28 and the LPF 32, and the upstream signal amplification circuit 24 amplifies each signal to a predetermined level. Will be output.
Further, between the HPF 26 and the HPF 28 constituting the upstream H signal input path, an auxiliary amplifier circuit 34 that amplifies the upstream H signal to a predetermined level, and an upstream H signal by the auxiliary amplifier circuit 34 and the upstream signal amplifier circuit 24. An equalizer 36 for adjusting the level of the upstream H signal is provided so that the amplification characteristic becomes a predetermined tilt characteristic (see FIG. 2). Further, between the LPF 30 and the LPF 32 constituting the uplink L signal input path, the uplink L signal is transmitted so that the amplification characteristic of the uplink L signal by the uplink signal amplification circuit 24 becomes a predetermined tilt characteristic (see FIG. 2). An equalizer 38 for adjusting the level is provided.
[0031]
Among the upstream signals amplified by the upstream signal amplification circuit 24, the upstream H signal includes an HPF 40 having a cutoff frequency of 650 MHz, an output level adjusting unit 42 for adjusting the output level of the upstream H signal, and a cutoff frequency of 650 MHz. The signal is output on the transmission line on the center apparatus side through an upstream H signal output path including the HPF 44, the above-described HPF 12, and the input terminal Tin. The upstream L signal is an upstream L signal output path including an LPF 46 with a cutoff frequency of 55 MHz, an output level adjusting unit 48 that adjusts the output level of the upstream L signal, an LPF 50 with a cutoff frequency of 55 MHz, and an input terminal Tin. Is output on the transmission line on the center device side.
[0032]
The output level adjusters 42 and 48 are respectively configured when the transmission line length of the center device side transmission line connected to the input terminal Tin is shorter than the set value and the amount of attenuation of the downstream signal generated in the transmission line is small. Input of the upstream signal to the upstream transmission device (or center device) provided on the center device side transmission line by attenuating the signal level of each upstream signal in accordance with the attenuation characteristic of each upstream signal on the transmission line The level is set to a predetermined constant level (pseudo line; so-called BON circuit).
[0033]
Therefore, as shown in FIG. 2, an upstream signal obtained by amplifying each upstream signal corresponding to the attenuation characteristic of the transmission line is output from the input terminal Tin to the center device side transmission line. Each upstream signal is input at a constant level to the preceding transmission device (or center device) provided on the side transmission line.
[0034]
2 shows a case where the line length of the transmission line on the center apparatus side to which the input terminal Tin is connected is a predetermined length set at the time of design (in other words, when the output level adjusting units 42 and 48 are not operated). , A specific example of each uplink signal output from the input terminal Tin to the transmission line on the center apparatus side is shown. For example, the relay amplifier has an uplink L signal output from the input terminal Tin of 87.6 dBμ at 10 MHz and 98 at 55 MHz. Each upstream signal is amplified so that the upstream H signal becomes 94.5 dBμ at 650 MHz and 95.8 dBμ at 770 MHz.
[0035]
Here, the HPFs 22, 26, 28 on the upstream H signal input path and the HPFs 40, 44, 12 on the upstream H signal output path are only upstream H signals among the signals flowing on the transmission line provided with the relay amplifier. Is selectively passed, and corresponds to the second filter circuit according to claim 1. The LPFs 30 and 32 on the upstream L signal input path and the LPFs 46 and 50 on the upstream L signal output path selectively pass only the upstream L signal among the signals flowing on the transmission line provided with the relay amplifier. And corresponds to the third filter circuit according to claim 1.
[0036]
Further, in the relay amplifier of the present embodiment, lightning strikes or the like occur on the transmission line provided with the relay amplifier between the input terminal Tin and the HPF 12 and LPF 50 and between the output terminal Tout and the HPF 22 and LPF 30, respectively. Lightning protection filters 52 and 54 are provided to protect the internal circuit from the induced high voltage.
[0037]
As described above, in the relay amplifier of this embodiment, the uplink H signal transmitted from the terminal side is input to the auxiliary amplifier circuit 34 via the HPF 22 and the HPF 26, whereby the uplink H signal is converted into the auxiliary amplifier circuit. 34, the signal is input to the upstream signal amplifier circuit 24 via the equalizer 36 and the HPF 28, and the upstream L signal transmitted from the terminal side is passed through the LPF 22, the equalizer 38, and the LPF 32. The signal is input to the upstream signal amplification circuit 24, and the upstream signal amplification circuit 24 amplifies the upstream H signal and the upstream L signal simultaneously.
[0038]
For this reason, according to the relay amplifier of this embodiment, the circuit configuration for upstream signal amplification is simplified and consumed compared to the conventional device that amplifies the upstream H signal and the upstream L signal by using dedicated amplifier circuits, respectively. Electric power can be reduced. Therefore, if a bidirectional CATV system is constructed using the relay amplifier of this embodiment, energy saving can be achieved in the entire system. In addition, since the amount of heat generated by the relay amplifier can be reduced along with the reduction in power consumption, the heat generation countermeasure parts (heat sink, heat dissipation fan, etc.) provided for countermeasures against the heat generation of the relay amplifier can be reduced in size. In addition, the relay amplifier can be reduced in size and weight.
[0039]
In this embodiment, in order to amplify the upstream H signal to a desired level, the upstream H signal is once amplified by the auxiliary amplifier circuit 34 and then input to the upstream signal amplifier circuit 24. Therefore, the gain of the upstream signal amplification circuit 24 can be reduced as compared with the case where the upstream H signal and the upstream L signal are amplified only by the upstream signal amplification circuit 24.
[0040]
That is, in order to obtain the upstream signal having the tilt characteristic shown in FIG. 2 using only the upstream signal amplifier circuit 24, the gain of the upstream signal amplifier circuit 24 can be amplified up to 95.8 dBμ at the maximum frequency (770 MHz). For this purpose, it is necessary to increase the number of amplifying elements (transistors) constituting the upstream signal amplifying circuit 24 or use an expensive transistor having a large amplification factor for each amplifying element. Disappear.
[0041]
However, in this embodiment, since the upstream H signal is amplified by the auxiliary amplifier circuit 34, for example, the gain of the upstream signal amplifier circuit 24 is set to 89.7 dBμ at the maximum frequency (55 MHz) of the upstream L signal. The auxiliary amplifier circuit 34 can compensate for the shortage of gain necessary to amplify the upstream L signal to a desired level.
[0042]
Therefore, according to the present embodiment, the gain of the upstream signal amplifying circuit 24 can be reduced as compared with the case where the upstream L signal and the upstream H signal are amplified only by the upstream signal amplifier circuit 24. Therefore, according to the present embodiment, the configuration of the upstream signal amplifier circuit 24 can be simplified and realized at a lower cost, and the power consumption can be reduced and the heat generation can be reduced by reducing the gain of the upstream signal amplifier circuit 24. The amount can be reduced.
[0043]
As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, A various aspect can be taken.
For example, in the above embodiment, the uplink H signal transmitted from the terminal side is amplified by the auxiliary amplifier circuit 34, and then the amplified uplink H signal and the uplink L signal transmitted from the terminal side are shared. Although the downstream signal amplified by the upstream signal amplifier circuit 24 and transmitted from the center device side has been described as being amplified by the downstream signal amplifier circuit 18, the ambient temperature and the like are used from the center device and terminal side. As shown in FIG. 3, in the case of a bidirectional CATV system in which a pilot signal (gain adjustment signal) for preventing level fluctuation of each transmission signal accompanying a change in attenuation characteristics of a transmission line caused by an environmental change is transmitted. The gain adjustment circuits 64 and 74 for adjusting the output levels of the downlink signal and the uplink signal may be provided for the downlink signal amplification circuit 18 and the uplink signal amplification circuit 24, respectively.
[0044]
That is, the relay amplifier shown in FIG. 3 is further different from the relay amplifier shown in FIG.
(1) A branch circuit 62 that branches a part of the downlink signal output from the downlink signal amplifier circuit 18.
(2) Attenuation for finely adjusting the slope characteristic of the output level of the downstream signal from the downstream signal amplifier circuit 18 provided between the upstream amplifier circuit 18a and the downstream amplifier circuit 18b in the downstream signal amplifier circuit 18. Instrument 66.
[0045]
(3) A downlink gain adjustment pilot signal transmitted from the center apparatus side is extracted from the downlink signals branched by the branch circuit 62 so that the signal level becomes a preset setting level. A gain adjustment circuit 64 that adjusts the gain of the entire downstream signal amplification circuit 18 by adjusting the attenuation amount of the attenuator 66.
[0046]
(4) A branch circuit 72 that is provided in an upstream H signal output path from the HPF 40 to the output level adjustment unit 42 and branches a part of the upstream H signal output from the upstream signal amplifier circuit 24.
(5) An output level of an upstream signal (specifically, an upstream H signal and an upstream L signal) from the upstream signal amplifier circuit 24 provided in an input path common to each upstream signal from the HPF 28 and the LPF 32 to the upstream signal amplifier circuit 24. An attenuator 76 for finely adjusting the inclination characteristics of
[0047]
(6) The uplink gain adjustment pilot signal transmitted from the terminal side is extracted from the uplink H signal branched by the branch circuit 72 so that the signal level becomes a preset setting level. A gain adjustment circuit 74 that adjusts the gain of the downstream signal amplification circuit 24 by adjusting the attenuation amount of the attenuator 76.
[0048]
The other configuration is exactly the same as that of the relay amplifier shown in FIG. 1, and operates in the same manner as the above embodiment.
The attenuator 66 for adjusting the downstream gain is set to have a constant attenuation amount (reference attenuation amount) in the entire frequency region of the downstream signal when the gain of the downstream signal amplification circuit 18 is an appropriate value. When the gain adjustment circuit 64 outputs a command to decrease the attenuation amount in order to increase the gain of the downstream signal amplification circuit 18, the attenuation amount is greatly decreased as the frequency is higher than the reference attenuation amount. When a command for increasing the amount of attenuation is output in order to reduce the gain of the signal amplifier circuit 18, the amount of attenuation increases greatly as the frequency is higher than the reference amount of attenuation.
[0049]
Further, the uplink gain adjusting attenuator 76 has a constant attenuation amount (reference attenuation amount) in the entire frequency region from the upstream L signal to the upstream H signal when the gain of the upstream signal amplification circuit 24 is at an appropriate value. When the gain adjustment circuit 74 outputs a command to decrease the attenuation amount in order to increase the gain of the upstream signal amplification circuit 24, the attenuation amount greatly decreases as the frequency is higher than the reference attenuation amount. When the gain adjustment circuit 74 outputs a command to increase the attenuation amount in order to decrease the gain of the upstream signal amplification circuit 26, the attenuation amount is greatly increased as the frequency is higher than the reference attenuation amount (FIG. 4). reference).
[0050]
This is because the gain of each of the amplifier circuits 18 and 24 is adjusted in accordance with the increase / decrease characteristic of the attenuation amount in the transmission line accompanying the temperature change of the transmission line.
In the relay amplifier of FIG. 3 configured as described above, the gain adjustment circuits 64 and 74 adjust the attenuation characteristics of the attenuators 66 and 76 based on the pilot signals transmitted from the center device and the terminal side, respectively. Thus, the gain of the downstream signal amplifier circuit 18 and upstream signal amplifier circuit 24 is adjusted, and the output level of the signal from each amplifier circuit 18 and 24 is set to the optimum level, so that the center device that transmits the downstream signal Even if the attenuation characteristics of the terminal-side transmission line and the terminal-side transmission line that transmits the upstream signal change depending on the usage environment such as temperature, it is possible to output each signal at an optimum level.
[0051]
Further, the upstream L signal and the upstream H signal are set to the optimum levels simply by adjusting the gain of the upstream signal amplifier 24 common to each signal, and it is necessary to provide a dedicated gain adjusting circuit for adjusting the level of each upstream signal. Therefore, the gain adjustment circuit can be simplified and the relay amplifier can be reduced in size and cost can be reduced as compared with the conventional apparatus in which each upstream signal is amplified by a dedicated amplifier circuit. .
[0052]
On the other hand, in the above-described embodiment, the case where the present invention is applied to a relay amplifier that simply amplifies each signal flowing in the trunk line or branch line of the bidirectional CATV system has been described. A branch circuit for branching the downstream signal amplified by the downstream signal amplifier circuit 18 to a lower transmission line (branch line), and each upstream signal transmitted from the terminal side via the branch line from the output terminal Tout The present invention can also be applied to a relay amplifier (so-called branch amplifier) provided with a mixing circuit that mixes with each input upstream signal and inputs to the upstream H signal input path and the upstream L signal input path. In such a relay amplifier (branch amplifier), the same effect as in the above embodiment can be obtained.
[0053]
Further, for example, in the above embodiment, the auxiliary amplifier circuit 34 that amplifies the upstream H signal is provided in the upstream H signal input path, and the upstream H signal amplified by the auxiliary amplifier circuit 34 is input to the upstream signal amplifier circuit 24. As described above, for example, the auxiliary amplifier circuit 34 is provided in the upstream H signal output path (more specifically, between the HPF 40 and the output level adjustment unit 42), and the upstream H signal output from the upstream signal amplifier circuit 24 is provided. The signal may be amplified by the auxiliary amplifier circuit 34.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a relay amplifier for a bidirectional CATV system according to an embodiment.
FIG. 2 is an explanatory diagram showing an upstream signal output from the input terminal Tin of the relay amplifier to the center device side.
FIG. 3 is a block diagram showing a configuration of a relay amplifier for a bidirectional CATV system including a gain adjustment circuit.
4 is an explanatory diagram for explaining attenuation characteristics of the gain adjusting attenuator shown in FIG. 3; FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 16 ... Input level adjustment part, 18 ... Downstream signal amplification circuit, 24 ... Upstream signal amplification circuit, 34 ... Auxiliary amplification circuit, 18c, 36, 38 ... Equalizer, 42, 48 ... Output level adjustment part, 52, 54 ... Lightning protection filter 12, 22, 26, 28, 40, 44... HPF (high pass filter), 14, 20, 30, 32, 46, 50... LPF (low pass filter), Tin... Input terminal, Tout. ... Branch circuit, 64, 74 ... Gain adjustment circuit, 66,76 ... Attenuator.

Claims

Than a downlink signal of a predetermined frequency band that is provided on a transmission line for signal transmission from the center device to the terminal side of the bidirectional CATV system and flows from the center device to the terminal side, and the downlink signal that flows from the terminal side to the center device side A bidirectional CATV system relay amplifier that amplifies an upstream L signal in a low frequency band and an upstream H signal in a frequency band higher than the downstream signal flowing from the terminal side to the center device side,
A downlink signal amplification circuit that amplifies the downlink signal transmitted from the center device side and outputs the amplified signal to the terminal side;
A signal in a downstream signal input path from the center apparatus side transmission line to the downstream signal amplifier circuit and a downstream signal output path from the downstream signal amplifier circuit to the terminal side transmission line, respectively, in the downstream signal frequency band A first filter circuit that selectively passes only components;
An upstream signal amplification circuit common to the upstream signals, amplifying an upstream signal obtained by mixing the upstream L signal and the upstream H signal transmitted from the terminal side, and outputting the amplified upstream signal to the center device side;
With
The upstream signal input path from the terminal side transmission line to the upstream signal amplifier circuit, and the upstream signal output path from the upstream signal amplifier circuit to the center apparatus side transmission line are each in two systems,
In each of the upstream signal input path and the upstream signal output path, a second filter circuit that selectively passes a signal component in the frequency band of the upstream H signal is provided.
The other upstream signal input path and upstream signal output path are each provided with a third filter circuit that selectively allows signal components in the frequency band of the upstream L signal to pass through,
In the two upstream signal input paths, the upstream H signal and upstream L signal are leveled so that the amplification characteristics of the upstream H signal and upstream L signal by the relay amplifier have a higher gain as the frequency becomes higher. Provide an equalizer to adjust,
Further, the upstream signal input path in which the second filter circuit is provided is provided with an auxiliary amplifier circuit for amplifying the upstream H signal so as to be in series with the equalizer. .

  Than a downlink signal of a predetermined frequency band that is provided on a transmission line for signal transmission from the center device to the terminal side of the bidirectional CATV system and flows from the center device to the terminal side, and the downlink signal that flows from the terminal side to the center device side A bidirectional CATV system relay amplifier that amplifies an upstream L signal in a low frequency band and an upstream H signal in a frequency band higher than the downstream signal flowing from the terminal side to the center device side,
  A downlink signal amplification circuit that amplifies the downlink signal transmitted from the center device side and outputs the amplified signal to the terminal side;
  A signal in a downstream signal input path from the center apparatus side transmission line to the downstream signal amplifier circuit and a downstream signal output path from the downstream signal amplifier circuit to the terminal side transmission line, respectively, in the downstream signal frequency band A first filter circuit that selectively passes only components;
  An upstream signal amplification circuit common to the upstream signals, amplifying an upstream signal obtained by mixing the upstream L signal and the upstream H signal transmitted from the terminal side, and outputting the amplified upstream signal to the center device side;
  With
  The upstream signal input path from the terminal side transmission line to the upstream signal amplifier circuit, and the upstream signal output path from the upstream signal amplifier circuit to the center apparatus side transmission line are each in two systems,
  In each of the upstream signal input path and the upstream signal output path, a second filter circuit that selectively passes a signal component in the frequency band of the upstream H signal is provided.
  The other upstream signal input path and upstream signal output path are each provided with a third filter circuit that selectively passes the signal component in the frequency band of the upstream L signal,
  The upstream signal output paths of the two systems are each provided with an output level adjustment unit that attenuates the upstream H signal and the upstream L signal in accordance with the attenuation characteristics of each upstream signal on the transmission line,
  The bidirectional CATV system further comprises an auxiliary amplifier circuit for amplifying the upstream H signal so that the upstream signal output path in which the second filter circuit is provided is in series with the output level adjustment unit. Relay amplifier.