JP5300703B2 - Video signal receiving apparatus and video transmission system - Google Patents

Video signal receiving apparatus and video transmission system Download PDF

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JP5300703B2
JP5300703B2 JP2009276082A JP2009276082A JP5300703B2 JP 5300703 B2 JP5300703 B2 JP 5300703B2 JP 2009276082 A JP2009276082 A JP 2009276082A JP 2009276082 A JP2009276082 A JP 2009276082A JP 5300703 B2 JP5300703 B2 JP 5300703B2
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JP2011120035A (en
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健志 登坂
佳伸 森田
徹 加沢
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本発明は、映像信号受信装置及び映像伝送システムに係り、特に、PON(Passive Optical Network)を用いたシステム等において、アナログ映像信号を伝送する映像信号受信装置及び映像伝送システムに関する。   The present invention relates to a video signal receiving apparatus and a video transmission system, and more particularly to a video signal receiving apparatus and a video transmission system for transmitting an analog video signal in a system using a PON (Passive Optical Network) or the like.

現在地上波、衛星放送、同軸ケーブルによるケーブルテレビなどで配信されているＴＶ信号を、光ファイバを用いて各家庭まで配信するシステムの導入が開始されている。既にＰＯＮ(Ｐａｓｓｉｖｅ Ｏｐｔｉｃａｌ Ｎｅｔｗｏｒｋ)を用いて構築されたＦＴＴＨ（Ｆｉｂｅｒ ｔｏ ｔｈｅ Ｈｏｍｅ）システムでは、例えば、電話局から家庭へのデータ伝送に１４９０ｎｍの波長を用い、家庭から電話局へのデータ伝送に１３１０ｎｍの波長を用い、この２つの波長を波長多重して１本のファイバで双方向のデータ通信を実現している。上記映像信号を１５５０ｎｍの波長の光信号に変換し、上記ファイバにさらに波長多重することで、既に設置された光ファイバを用いてテレビ向けのアナログ信号を伝送することが可能となっている。   Introduction of a system that distributes TV signals currently distributed by terrestrial, satellite broadcasting, cable television using a coaxial cable, etc. to homes using optical fibers has been started. In an FTTH (Fiber to the Home) system already built using PON (Passive Optical Network), for example, a wavelength of 1490 nm is used for data transmission from a telephone station to a home, and 1310 nm is used for data transmission from the home to the telephone station. These two wavelengths are wavelength-multiplexed to realize bidirectional data communication using a single fiber. By converting the video signal into an optical signal having a wavelength of 1550 nm and further wavelength-multiplexing the optical signal, it is possible to transmit an analog signal for television using an already installed optical fiber.

通常、テレビプログラムはテレビチャネル毎に異なる周波数の搬送波を用いてアナログ変調され、変調後の信号は例えば、６ＭＨｚ間隔で周波数多重されて送信されている。この信号をさらに電気信号から上記光信号に変換することで、光ファイバを用いた伝送が可能となっている。このように複数の搬送波を束ねて伝送する方法は、ＳＣＭ（Ｓｕｂ Ｃａｒｒｉｅｒ Ｍｕｌｔｉｐｌｅｘｉｎｇ）と呼ばれている。   Usually, a television program is analog-modulated using a carrier wave having a different frequency for each television channel, and the modulated signal is frequency-multiplexed and transmitted at intervals of 6 MHz, for example. By further converting this signal from an electrical signal to the optical signal, transmission using an optical fiber is possible. Such a method of bundling and transmitting a plurality of carrier waves is called SCM (Sub Carrier Multiplexing).

品質の良好な映像信号は、例えば、５０ｄＢ程度のＣ／Ｎ（キャリア／ノイズ比）を保ったまま伝送される必要があるが、光ファイバ伝送においてはファイバの接続点による光反射などの影響で、上記Ｃ／Ｎが３０ｄＢ程度まで悪化してしまうことがある。この状況でも映像信号の品質を保つため、振幅歪に強い耐性を持つＦＭ変調技術を応用し、上記ＳＣＭ信号を一括してＦＭ変調して伝送するＦＭ一括変調技術が実用化されている。そして、上記技術によって伝送された映像信号は、家庭内に設置された受信器であるＶ−ＯＮＵ(Ｖｉｄｅｏ Ｏｐｔｉｃａｌ Ｎｅｔｗｏｒｋ Ｕｎｉｔ)内で光−電気変換された後にＦＭ一括復調され、家庭内の同軸ケーブルを用いてテレビまで配信されている。この技術の詳細は、たとえば特開２００１−１１９０９７に開示されているものである。   For example, a video signal with good quality needs to be transmitted while maintaining a C / N (carrier / noise ratio) of about 50 dB. However, in optical fiber transmission, it is affected by light reflection at the connection point of the fiber. The C / N may be deteriorated to about 30 dB. In order to maintain the quality of the video signal even in this situation, the FM batch modulation technology that applies FM modulation technology that has strong resistance to amplitude distortion and FM modulates the SCM signals collectively and transmits them has been put into practical use. The video signal transmitted by the above technique is optically-electrically converted in a V-ONU (Video Optical Network Unit) which is a receiver installed in the home, and then FM is demodulated, and the coaxial cable in the home is used. It is distributed to TV using. Details of this technique are disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-119097.

特開２００１−１１９０９７号公報Japanese Patent Laid-Open No. 2001-119097

上記従来技術においては、角度変調の一種であるＦＭ変調が用いられているがゆえに、信号の振幅成分の歪ではなく、時間方向の歪である信号幅歪が被変調信号の品質劣化の主要因となるという特徴を持っている。   In the above prior art, since FM modulation, which is a kind of angle modulation, is used, signal width distortion, which is distortion in the time direction, and not distortion of the amplitude component of the signal, is the main factor of quality deterioration of the modulated signal. It has the feature of becoming.

伝送路上の光ファイバの非線形特性により生じる負方向(プラス方向の成分の信号が細る方向)の信号幅歪や、Ｖ−ＯＮＵ等の受信システム内部の回路素子の非線形特性により生じる正方向(プラス方向の成分の信号が太る方向)の信号幅歪が上記信号幅歪の要因であるが、特に光ファイバによる映像信号伝送では、上記高いＣ／Ｎを得るために許される限り大きい伝送電力で信号伝送を行うことが多く、上記光ファイバの非線形特性や回路素子の非線形特性が映像品質に大きな悪影響を与えてしまうという課題があった。   Positive direction (plus direction) caused by signal width distortion in the negative direction (direction in which the signal of the plus direction component is narrowed) caused by nonlinear characteristics of the optical fiber on the transmission line and nonlinear characteristics of circuit elements inside the receiving system such as V-ONU Signal width distortion in the direction in which the component signal becomes thicker) is a factor of the signal width distortion. Particularly in video signal transmission by optical fiber, signal transmission is performed with a transmission power as high as possible to obtain the high C / N. There is a problem that the nonlinear characteristics of the optical fiber and the nonlinear characteristics of the circuit elements have a great adverse effect on the video quality.

本発明は、以上の点に鑑み、ＦＭ一括変換方式を用いた映像伝送システムにおいて、より高い品質で映像信号を伝送することを目的とする。また、本発明は、ＦＭ一括変換方式を用いた映像伝送システムにおいて、伝送路の非線形特性により生じる負方向の信号幅歪、又は、装置の非線形特性により生じる正方向の信号幅歪、又は、これら両方の信号幅歪による映像及び音声等の信号品質の劣化を軽減することを目的とするものである。   In view of the above, an object of the present invention is to transmit a video signal with higher quality in a video transmission system using the FM batch conversion method. Also, the present invention provides a negative signal width distortion caused by nonlinear characteristics of a transmission line, or a positive signal width distortion caused by nonlinear characteristics of a device in a video transmission system using the FM batch conversion method, or these The object is to reduce the degradation of signal quality such as video and audio due to both signal width distortions.

本発明では、上記課題を解決する方法として、概略以下のような方法で信号幅歪を補正する。
Ｖ−ＯＮＵにおいて受信したＦＭ一括変換信号を光―電気変換した後、ＦＭ一括復調する前に、入力信号の振幅に依存した利得を持つ差動増幅器を設置し、上記差動増幅器の一方の入力端子に上記電気変換されたＦＭ一括変換信号を入力し、他方の入力端子に比較しきい値電圧を与える。差動増幅器の利得は、しきい値電圧近傍では高い利得を、しきい値より離れるほど低い利得を持たせておく。上記差動増幅器は、しきい値に近い部分の信号を大きな利得で増幅し、しきい値から離れた部分の信号を小さな利得で増幅するため、入力信号としきい値が交わる付近の信号幅を強調して再生するように信号を歪ませる効果が得られる。たとえば正弦波状の信号を本差動増幅器入力する時、正方向振幅の信号と負方向振幅の信号が同じ幅である正弦波状の信号の中心値にしきい値が一致していれば、増幅後の信号は振幅の両端での振幅歪が発生する場合があるものの正方向の信号と負方向の信号が同じ幅に保たれた出力が得られる。しきい値を下げると正方向振幅の信号に比べて負方向振幅の信号がより増幅されるため、正方向の信号の幅は広く、負方向の信号の幅が狭い出力が得られる。これは、入力信号の信号幅が広くなる方向に歪を与えたことに相当する。逆に、しきい値を上げると負方向振幅の信号に比べて正方向振幅の信号がより増幅されるため、正方向の信号の幅は狭く、負方向の信号の幅が広い出力が得られる。これは、入力信号の信号幅が狭くなる方向に歪を与えたことに相当する。したがって、ＦＭ一括変換信号の信号幅歪を測定した後、この作用を用いて、信号幅歪に応じて上記しきい値電圧を増減させることで、信号幅歪を減少させた信号を得ることが可能となる。 In the present invention, as a method for solving the above-described problem, signal width distortion is corrected by the following method.
A differential amplifier having a gain depending on the amplitude of the input signal is installed after FM-to-electrical conversion of the FM batch conversion signal received at the V-ONU and before FM batch demodulation, and one input of the differential amplifier The above-mentioned FM batch conversion signal obtained by electrical conversion is input to a terminal, and a comparison threshold voltage is applied to the other input terminal. The gain of the differential amplifier has a high gain in the vicinity of the threshold voltage, and a lower gain as the distance from the threshold increases. The differential amplifier amplifies the signal near the threshold with a large gain and amplifies the signal far from the threshold with a small gain, so the signal width near the intersection of the input signal and the threshold is reduced. An effect of distorting the signal so as to be reproduced with emphasis can be obtained. For example, when a sine wave signal is input to this differential amplifier, if the threshold value matches the center value of the sine wave signal having the same width as the positive amplitude signal and the negative amplitude signal, Although the signal may have amplitude distortion at both ends of the amplitude, an output in which the signal in the positive direction and the signal in the negative direction are maintained at the same width is obtained. When the threshold value is lowered, a signal with a negative direction amplitude is amplified more than a signal with a positive direction amplitude. Therefore, an output with a wide width in the positive direction signal and a narrow width in the negative direction signal can be obtained. This corresponds to applying distortion in the direction in which the signal width of the input signal becomes wider. On the other hand, when the threshold value is raised, the positive amplitude signal is amplified more than the negative amplitude signal, so that the positive signal width is narrow and the negative signal width is wide. . This corresponds to applying distortion in the direction in which the signal width of the input signal becomes narrower. Therefore, after measuring the signal width distortion of the FM batch conversion signal, this signal can be used to increase or decrease the threshold voltage according to the signal width distortion to obtain a signal with reduced signal width distortion. It becomes possible.

信号幅歪を検出する具体的なひとつの手段として、ＦＭ一括変調キャリアレベルを検出する方法が有効である。無歪のＦＭ一括変調信号をＦＭ復調するとＦＭ一括変調キャリアは完全に除去されるが、信号幅歪を被ったＦＭ一括変調信号をＦＭ復調するとＦＭ一括変調キャリアが残留することが知られている。残留するキャリアレベルの大きさは信号幅歪が大きいほど大きい。ただし、無歪の信号の信号幅を広くする方向の歪（以後、正の信号幅歪と呼ぶ）でも狭くする方向の歪(以後、負の信号幅歪と呼ぶ)でもＦＭ一括変調キャリアが残留するため、残留キャリアレベルの値から直接信号幅歪の符号（正の信号幅歪か負の信号幅歪か）を求めることができない。したがって、しきい値の調整は、以下の手順を踏んで行う。   As a specific means for detecting the signal width distortion, a method of detecting the FM batch modulation carrier level is effective. It is known that when FM demodulation is performed on an undistorted FM batch modulation signal, the FM batch modulation carrier is completely removed, but when FM demodulation is performed on an FM batch modulation signal subjected to signal width distortion, the FM batch modulation carrier remains. . The magnitude of the remaining carrier level increases as the signal width distortion increases. However, the FM collective modulation carrier remains in both a distortion in the direction of widening the signal width of the undistorted signal (hereinafter referred to as positive signal width distortion) and a distortion in the direction of narrowing (hereinafter referred to as negative signal width distortion). Therefore, the sign of signal width distortion (whether positive signal width distortion or negative signal width distortion) cannot be obtained directly from the value of the residual carrier level. Therefore, the threshold value is adjusted according to the following procedure.

まず初期状態にてしきい値を中央値に設定しておく。信号を受信すると、キャリア周波数に合わせたバンドパスフィルタおよびレベル検出器を用いてＦＭ一括キャリアレベルをモニタしておく。無歪条件ではゼロとなるべきキャリアレベルが、所定の値よりも低ければ信号幅歪は十分小さく、映像品質が高い状態である。キャリアレベルが所定の値よりも高ければ、許容以上の信号幅歪が発生しているとみなせる。ここでまず増幅器しきい値を減少方向にあらかじめ定めた１単位の電圧だけ変化させる。この結果、もしキャリアレベルが減少すれば、負方向に存在した信号幅歪に正の方向の信号幅歪が加えられて、最終的な歪が減少した可能性が高いと考えられる。続いて増幅器しきい値を増加方向にあらかじめ定めた１単位の電圧だけ変化させる。もしキャリアレベルが増加すれば、やはり負方向に存在した信号幅歪に、負方向の信号幅歪がさらに加えられて最終的な歪が増加した可能性が高いと考えられる。こうして、しきい値の増減の方向とキャリアレベルの増減の相関がとれれば、キャリアレベルが所定の値より小さくなるまで上記しきい値を変化させれば信号幅歪を補正することが可能となる。なお、正方向に存在した信号幅歪についても、同様にしきい値の調整をすることができる。   First, the threshold value is set to the median value in the initial state. When the signal is received, the FM collective carrier level is monitored using a bandpass filter and a level detector matched to the carrier frequency. If the carrier level that should be zero under the no distortion condition is lower than a predetermined value, the signal width distortion is sufficiently small and the video quality is high. If the carrier level is higher than a predetermined value, it can be considered that signal width distortion more than allowable is generated. Here, the amplifier threshold value is first changed in a decreasing direction by a predetermined unit voltage. As a result, if the carrier level decreases, it is highly likely that the signal width distortion in the positive direction is added to the signal width distortion existing in the negative direction, and the final distortion is reduced. Subsequently, the amplifier threshold value is changed by a predetermined unit voltage in the increasing direction. If the carrier level increases, there is a high possibility that the final distortion is increased by further adding the negative signal width distortion to the negative signal width distortion. Thus, if the increase / decrease direction of the threshold is correlated with the increase / decrease of the carrier level, the signal width distortion can be corrected by changing the threshold until the carrier level becomes smaller than a predetermined value. . It should be noted that the threshold value can be adjusted similarly for the signal width distortion existing in the positive direction.

ただし、信号幅歪が大きい場合、１単位のしきい値電圧の変化ではキャリアレベルの変化が検出できない可能性がある。あるいは雑音により、しきい値を増加させても減少させてもキャリアレベルが増加する場合、しきい値を増加させても減少させてもキャリアレベルが減少する場合も考えられる。この場合、上記しきい値電圧を２単位、３単位と増加させていきながら繰り返しキャリアレベルをモニタすることにより、いずれかの電圧でしきい値の増減の方向とキャリアレベルの増減の相関がとれるようになる。   However, when the signal width distortion is large, a change in carrier level may not be detected by a change in threshold voltage of one unit. Alternatively, due to noise, the carrier level may increase when the threshold value is increased or decreased, and the carrier level may decrease when the threshold value is increased or decreased. In this case, by repeatedly monitoring the carrier level while increasing the threshold voltage to 2 units or 3 units, the direction of increase or decrease of the threshold value can be correlated with the increase or decrease of the carrier level at any voltage. It becomes like this.

本発明の第１の解決手段によると、
複数の映像信号を異なる搬送波で変調して周波数多重及びＦＭ一括変調して、光信号として送信する送信装置と、上記送信装置から出力された光信号を伝送する光ファイバ網と、上記光ファイバ網から光信号を受信してひとつ又は複数の映像信号に復調する受信装置とを備えた映像伝送システムにおける、映像信号受信装置であって、
上記光ファイバ網からの光信号を受信して光―電気変換する光−電気変換部と、
一方の入力端子を上記光―電気変換部の出力に接続され、他方の入力端子にしきい値が入力され、しきい値電圧近傍では高い利得を、しきい値より離れるほど低い利得を持つような、入力信号の振幅に依存した利得を持つ差動増幅器と、
上記差動増幅器からの出力をＦＭ一括復調するＦＭ一括復調部と、
上記ＦＭ一括復調部の出力から、ＦＭ一括復調の信号幅歪が大きいほど大きい値を示すＦＭ一括変調のキャリア周波数の、ＦＭ一括キャリアレベルを検出する信号幅歪検出部と、
上記信号幅歪検出部の出力から、信号幅歪に応じた補正しきい値を生成し、該補正しきい値を上記差動増幅器の他方の入力端子に出力する補正しきい値生成部と、
を備え、

上記補正しきい値生成部は、
初期状態にてしきい値を中央値に設定してＦＭ一括キャリアレベルをモニタし、
しきい値を減少方向に変化させてＦＭ一括キャリアレベルの第１の変化量を求め、
しきい値を増加方向に変化させてＦＭ一括キャリアレベルの第２の変化量を求め、
上記第１及び第２の変化量に基づきしきい値を減少又は増加させることにより、ＦＭ一括キャリアレベルが予め定めた許容値以下になるようにしきい値の増加又は減少の変化方向と変化量とを調整し、
しきい値を減少させることで、プラス方向の成分の信号幅が時間方向に細くなる負方向の信号幅歪を減少させ、又は、しきい値を増加させることで、プラス方向の成分の信号幅が時間方向に太くなる正方向の信号幅歪を減少させるための、補正しきい値を求めるようにした、
前記映像信号受信装置が提供される。 According to the first solution of the present invention,
A transmission apparatus that modulates a plurality of video signals with different carrier waves, performs frequency multiplexing and FM batch modulation, and transmits them as an optical signal; an optical fiber network that transmits an optical signal output from the transmission apparatus; and the optical fiber network A video signal receiving device in a video transmission system comprising a receiving device that receives an optical signal from and demodulates into one or a plurality of video signals,
An optical-electrical converter that receives an optical signal from the optical fiber network and performs optical-electrical conversion;
One input terminal is connected to the output of the opto-electric converter, the other input terminal has a threshold value input, and a high gain is obtained in the vicinity of the threshold voltage, and a lower gain is obtained as the distance from the threshold value increases. A differential amplifier having a gain depending on the amplitude of the input signal;
An FM batch demodulator for FM demodulating the output from the differential amplifier;
A signal width distortion detection unit for detecting an FM collective carrier level of an FM collective modulation carrier frequency that indicates a larger value as the signal width distortion of the FM collective demodulation increases from the output of the FM collective demodulation unit;
A correction threshold value generating unit that generates a correction threshold value according to the signal width distortion from the output of the signal width distortion detection unit, and outputs the correction threshold value to the other input terminal of the differential amplifier;
With

The correction threshold value generator is
In the initial state, set the threshold value to the median value and monitor the FM batch carrier level.
The threshold value is changed in the decreasing direction to obtain the first change amount of the FM collective carrier level,
The threshold value is changed in the increasing direction to obtain the second change amount of the FM collective carrier level,
By decreasing or increasing the threshold based on the first and second change amounts, the change direction and change amount of the threshold increase or decrease so that the FM collective carrier level is equal to or less than a predetermined allowable value. Adjust
Decreasing the threshold value reduces the signal width distortion in the negative direction where the signal width of the positive direction component becomes narrower in the time direction, or increasing the threshold value increases the signal width of the positive direction component. The correction threshold value is calculated to reduce the signal width distortion in the positive direction that becomes thicker in the time direction.
The video signal receiving apparatus is provided.

本発明の第２の解決手段によると、
複数の映像信号を異なる搬送波で変調して周波数多重及びＦＭ一括変調して、光信号として送信する送信装置と、上記送信装置から出力された光信号を伝送する光ファイバ網と、上記光ファイバ網から光信号を受信してひとつ又は複数の映像信号に復調する受信装置とを備えた映像伝送システムにおける、映像信号受信装置であって、
上記光ファイバ網からの光信号を受信して光―電気変換する光−電気変換部と、
一方の入力端子を上記光―電気変換部の出力に接続され、他方の入力端子にしきい値が入力され、しきい値電圧近傍では高い利得を、しきい値より離れるほど低い利得を持つような、入力信号の振幅に依存した利得を持つ差動増幅器と、
上記差動増幅器からの出力をＦＭ一括復調するＦＭ一括復調部と、
残留キャリア成分を抽出するためのバンドパスフィルタと、前記バンドパスフィルタの出力を保持するための抵抗とコンデンサを含む回路とを備え、上記ＦＭ一括復調部の出力から、ＦＭ一括復調の信号幅歪が大きいほど大きい値を示すＦＭ一括変調のキャリア周波数の、ＦＭ一括キャリアレベルを抽出し保持する残留キャリア成分抽出回路と、
上記残留キャリア成分抽出回路の出力から、予め定められた比較しきい値電圧と比較する比較器を有し、補正信号を出力するキャリアリーク量判定回路と、
を備え、
上記キャリアリーク量判定回路の上記比較器から出力される補正信号で上記差動増幅器のしきい値電圧を調整することにより、主要因が光伝送中の非線形効果によるパルス圧縮による信号幅歪又はプラス方向の成分の信号幅が時間方向に細くなる負方向の信号幅歪を減少させるようにした、
前記映像信号受信装置が提供される。 According to the second solution of the present invention,
A transmission apparatus that modulates a plurality of video signals with different carrier waves, performs frequency multiplexing and FM batch modulation, and transmits them as an optical signal; an optical fiber network that transmits an optical signal output from the transmission apparatus; and the optical fiber network A video signal receiving device in a video transmission system comprising a receiving device that receives an optical signal from and demodulates into one or a plurality of video signals,
An optical-electrical converter that receives an optical signal from the optical fiber network and performs optical-electrical conversion;
One input terminal is connected to the output of the opto-electric converter, the other input terminal has a threshold value input, and a high gain is obtained in the vicinity of the threshold voltage, and a lower gain is obtained as the distance from the threshold value increases. A differential amplifier having a gain depending on the amplitude of the input signal;
An FM batch demodulator for FM demodulating the output from the differential amplifier;
A band pass filter for extracting a residual carrier component; and a circuit including a resistor and a capacitor for holding the output of the band pass filter, and the signal width distortion of FM collective demodulation from the output of the FM collective demodulation unit A residual carrier component extraction circuit that extracts and holds an FM collective carrier level of an FM collective modulation carrier frequency that indicates a larger value as
A carrier leak amount determination circuit that has a comparator for comparing with a predetermined comparison threshold voltage from an output of the residual carrier component extraction circuit and outputs a correction signal;
With
By adjusting the threshold voltage of the differential amplifier with the correction signal output from the comparator of the carrier leak amount determination circuit, the main factor is signal width distortion due to non-linear effects during optical transmission, or plus The signal width distortion in the negative direction where the signal width of the direction component becomes narrower in the time direction has been reduced.
The video signal receiving apparatus is provided.

本発明の第３の解決手段によると、
複数の映像信号を異なる搬送波で変調して周波数多重及びＦＭ一括変調して、光信号として送信する送信装置と、上記送信装置から出力された光信号を伝送する光ファイバ網と、上記光ファイバ網から光信号を受信してひとつ又は複数の映像信号に復調する受信装置とを備えた映像伝送システムにおいて、

上記送信装置は、
複数の映像信号をそれぞれ異なる周波数を持つ複数の搬送波を用いて変調する複数の変調部と、
上記複数の変調部によりそれぞれ複数の搬送波を用いて変調された複数の映像信号を周波数多重し、ＦＭ一括変調し、電気―光変換して送信するＦＭ一括変調部と、
を備え、

上記受信装置は、
上記光ファイバ網からの光信号を受信して光―電気変換する光−電気変換部と、
一方の入力端子を上記光―電気変換部の出力に接続され、他方の入力端子にしきい値が入力され、しきい値電圧近傍では高い利得を、しきい値より離れるほど低い利得を持つような、入力信号の振幅に依存した利得を持つ差動増幅器と、
上記差動増幅器からの出力をＦＭ一括復調するＦＭ一括復調部と、
上記ＦＭ一括復調部の出力から、ＦＭ一括復調の信号幅歪が大きいほど大きい値を示すＦＭ一括変調のキャリア周波数の、ＦＭ一括キャリアレベルを検出する信号幅歪検出部と、
上記信号幅歪検出部の出力から、信号幅歪に応じた補正しきい値を生成し、該補正しきい値を上記差動増幅器の他方の入力端子に出力する補正しきい値生成部と、
を備え、
上記補正しきい値生成部は、
初期状態にてしきい値を中央値に設定してＦＭ一括キャリアレベルをモニタし、
しきい値を減少方向に変化させてＦＭ一括キャリアレベルの第１の変化量を求め、
しきい値を増加方向に変化させてＦＭ一括キャリアレベルの第２の変化量を求め、
上記第１及び第２の変化量に基づきしきい値を減少又は増加させることにより、ＦＭ一括キャリアレベルが予め定めた許容値以下になるようにしきい値の増加又は減少の変化方向と変化量とを調整し、
しきい値を減少させることで、プラス方向の成分の信号幅が時間方向に細くなる負方向の信号幅歪を減少させ、又は、しきい値を増加させることで、プラス方向の成分の信号幅が時間方向に太くなる正方向の信号幅歪を減少させるための、補正しきい値を求めるようにした、
前記映像伝送システムが提供される。 According to the third solution of the present invention,
A transmission apparatus that modulates a plurality of video signals with different carrier waves, performs frequency multiplexing and FM batch modulation, and transmits them as an optical signal; an optical fiber network that transmits an optical signal output from the transmission apparatus; and the optical fiber network In a video transmission system comprising a receiving device that receives an optical signal from and demodulates into one or a plurality of video signals,

The transmitter is
A plurality of modulation sections that modulate a plurality of video signals using a plurality of carrier waves having different frequencies, and
An FM batch modulation unit that frequency-multiplexes a plurality of video signals modulated by a plurality of carrier waves by the plurality of modulation units, performs FM batch modulation, performs electro-optical conversion, and transmits;
With

The receiving device is
An optical-electrical converter that receives an optical signal from the optical fiber network and performs optical-electrical conversion;
One input terminal is connected to the output of the opto-electric converter, the other input terminal has a threshold value input, and a high gain is obtained in the vicinity of the threshold voltage, and a lower gain is obtained as the distance from the threshold value increases. A differential amplifier having a gain depending on the amplitude of the input signal;
An FM batch demodulator for FM demodulating the output from the differential amplifier;
A signal width distortion detection unit for detecting an FM collective carrier level of an FM collective modulation carrier frequency that indicates a larger value as the signal width distortion of the FM collective demodulation increases from the output of the FM collective demodulation unit;
A correction threshold value generating unit that generates a correction threshold value according to the signal width distortion from the output of the signal width distortion detection unit, and outputs the correction threshold value to the other input terminal of the differential amplifier;
With
The correction threshold value generator is
In the initial state, set the threshold value to the median value and monitor the FM batch carrier level.
The threshold value is changed in the decreasing direction to obtain the first change amount of the FM collective carrier level,
The threshold value is changed in the increasing direction to obtain the second change amount of the FM collective carrier level,
By decreasing or increasing the threshold based on the first and second change amounts, the change direction and change amount of the threshold increase or decrease so that the FM collective carrier level is equal to or less than a predetermined allowable value. Adjust
Decreasing the threshold value reduces the signal width distortion in the negative direction where the signal width of the positive direction component becomes narrower in the time direction, or increasing the threshold value increases the signal width of the positive direction component. The correction threshold value is calculated to reduce the signal width distortion in the positive direction that becomes thicker in the time direction.
The video transmission system is provided.

本発明の第４の解決手段によると、
複数の映像信号を異なる搬送波で変調して周波数多重及びＦＭ一括変調して、光信号として送信する送信装置と、上記送信装置から出力された光信号を伝送する光ファイバ網と、上記光ファイバ網から光信号を受信してひとつ又は複数の映像信号に復調する受信装置とを備えた映像伝送システムにおいて、

上記送信装置は、
複数の映像信号をそれぞれ異なる周波数を持つ複数の搬送波を用いて変調する複数の変調部と、
上記複数の変調部によりそれぞれ複数の搬送波を用いて変調された複数の映像信号を周波数多重し、ＦＭ一括変調し、電気―光変換して送信するＦＭ一括変調部と、
を備え、

上記受信装置は、
上記光ファイバ網からの光信号を受信して光―電気変換する光−電気変換部と、
一方の入力端子を上記光―電気変換部の出力に接続され、他方の入力端子にしきい値が入力され、しきい値電圧近傍では高い利得を、しきい値より離れるほど低い利得を持つような、入力信号の振幅に依存した利得を持つ差動増幅器と、
上記差動増幅器からの出力をＦＭ一括復調するＦＭ一括復調部と、
残留キャリア成分を抽出するためのバンドパスフィルタと、前記バンドパスフィルタの出力を保持するための抵抗とコンデンサを含む回路とを備え、上記ＦＭ一括復調部の出力から、ＦＭ一括復調の信号幅歪が大きいほど大きい値を示すＦＭ一括変調のキャリア周波数の、ＦＭ一括キャリアレベルを抽出し保持する残留キャリア成分抽出回路と、
上記残留キャリア成分抽出回路の出力から、予め定められた比較しきい値電圧と比較する比較器を有し、補正信号を出力するキャリアリーク量判定回路と、
を備え、
上記キャリアリーク量判定回路の上記比較器から出力される補正信号で上記差動増幅器のしきい値電圧を調整することにより、主要因が光伝送中の非線形効果によるパルス圧縮による信号幅歪又はプラス方向の成分の信号幅が時間方向に細くなる負方向の信号幅歪を減少させるようにした、
前記映像伝送システムが提供される。 According to the fourth solution of the present invention,
A transmission apparatus that modulates a plurality of video signals with different carrier waves, performs frequency multiplexing and FM batch modulation, and transmits them as an optical signal; an optical fiber network that transmits an optical signal output from the transmission apparatus; and the optical fiber network In a video transmission system comprising a receiving device that receives an optical signal from and demodulates into one or a plurality of video signals,

The transmitter is
A plurality of modulation sections that modulate a plurality of video signals using a plurality of carrier waves having different frequencies, and
An FM batch modulation unit that frequency-multiplexes a plurality of video signals modulated by a plurality of carrier waves by the plurality of modulation units, performs FM batch modulation, performs electro-optical conversion, and transmits;
With

The receiving device is
An optical-electrical converter that receives an optical signal from the optical fiber network and performs optical-electrical conversion;
One input terminal is connected to the output of the opto-electric converter, the other input terminal has a threshold value input, and a high gain is obtained in the vicinity of the threshold voltage, and a lower gain is obtained as the distance from the threshold value increases. A differential amplifier having a gain depending on the amplitude of the input signal;
An FM batch demodulator for FM demodulating the output from the differential amplifier;
A band pass filter for extracting a residual carrier component; and a circuit including a resistor and a capacitor for holding the output of the band pass filter, and the signal width distortion of FM collective demodulation from the output of the FM collective demodulation unit A residual carrier component extraction circuit that extracts and holds an FM collective carrier level of an FM collective modulation carrier frequency that indicates a larger value as
A carrier leak amount determination circuit that has a comparator for comparing with a predetermined comparison threshold voltage from an output of the residual carrier component extraction circuit and outputs a correction signal;
With
By adjusting the threshold voltage of the differential amplifier with the correction signal output from the comparator of the carrier leak amount determination circuit, the main factor is signal width distortion due to non-linear effects during optical transmission, or plus The signal width distortion in the negative direction where the signal width of the direction component becomes narrower in the time direction has been reduced.
The video transmission system is provided.

本発明により、ＦＭ一括変換方式を用いてより高い品質で映像信号を伝送することが可能となる。
また、本発明によると、ＦＭ一括変換方式を用いた映像伝送システムにおいて、伝送路の非線形特性により生じる負方向の信号幅歪、又は、装置の非線形特性により生じる正方向の信号幅歪、又は、これら両方の信号幅歪による映像及び音声等の信号品質の劣化を軽減することができる。 According to the present invention, it is possible to transmit a video signal with higher quality using the FM batch conversion method.
According to the present invention, in the video transmission system using the FM batch conversion method, the negative signal width distortion caused by the nonlinear characteristic of the transmission path, or the positive signal width distortion caused by the nonlinear characteristic of the device, or It is possible to reduce degradation of signal quality such as video and audio due to both signal width distortions.

ＦＭ一括変調伝送システムの構成図を示す。The block diagram of FM batch modulation transmission system is shown. ＦＭ一括変調方式の図を示す。The figure of FM batch modulation system is shown. 本発明の実施の形態のＶ−ＯＮＵの構成図を示す。The block diagram of V-ONU of embodiment of this invention is shown. 本発明の実施の形態の増幅器の特性を示す。The characteristic of the amplifier of embodiment of this invention is shown. 本発明の実施の形態の増幅器のしきい値と出力信号の関係を示す。The relationship between the threshold value of the amplifier of an embodiment of the invention and an output signal is shown. 本発明の実施の形態の増幅器のしきい値と出力信号の関係を示す。The relationship between the threshold value of the amplifier of an embodiment of the invention and an output signal is shown. 本発明の実施の形態の増幅器のしきい値と出力信号の関係を示す。The relationship between the threshold value of the amplifier of an embodiment of the invention and an output signal is shown. 本発明の実施の形態１のフローチャートを示す。The flowchart of Embodiment 1 of this invention is shown. 本発明の実施の形態の増幅器のしきい値と入出力信号の関係を示す。The relationship between the threshold value and input / output signal of the amplifier according to the embodiment of the present invention is shown. 本発明の実施の形態の増幅器のしきい値と入出力信号の関係を示す。The relationship between the threshold value and input / output signal of the amplifier according to the embodiment of the present invention is shown. 本発明の実施の形態の増幅器のしきい値と信号幅歪の関係を示す。The relationship between the threshold value and the signal width distortion of the amplifier according to the embodiment of the present invention is shown. 本発明の実施の形態２のフローチャートを示す。The flowchart of Embodiment 2 of this invention is shown. 本発明の実施の形態３のフローチャートを示す。The flowchart of Embodiment 3 of this invention is shown. 本発明の実施の形態４のフローチャートを示す。The flowchart of Embodiment 4 of this invention is shown. 本発明の実施の形態３、実施の形態４にて用いるしきい値制御テーブルの構成図を示す。The block diagram of the threshold value control table used in Embodiment 3 and Embodiment 4 of this invention is shown. 本発明の実施の形態５のＶ−ＯＮＵの構成図を示す。The block diagram of V-ONU of Embodiment 5 of this invention is shown. 本発明の実施の形態３のＶ−ＯＮＵの構成図を示す。The block diagram of V-ONU of Embodiment 3 of this invention is shown.

１．システム
図１は、ＦＭ一括変調伝送システムの構成図を示す。
映像送信システム１は、複数の映像ソース２０の信号をそれぞれ異なる周波数を持つ複数の搬送波を用いて変調する複数のサブキャリア変調部２１と、複数のサブキャリア変調部２１から出力された信号を周波数多重し、ＦＭ一括変調し、電気―光変換して出力するＦＭ一括変調部２２を備える。そして、映像システム１から出力された上記信号を増幅して分配する光アンプ２を介してＷＤＭカプラ５の一端に接続される。 1. System FIG. 1 shows a configuration diagram of an FM batch modulation transmission system.
The video transmission system 1 includes a plurality of subcarrier modulation units 21 that modulate signals of a plurality of video sources 20 using a plurality of carrier waves having different frequencies, and signals output from the plurality of subcarrier modulation units 21 as frequencies. An FM batch modulation unit 22 that multiplexes, FM batch modulates, and performs electrical-optical conversion to output is provided. Then, it is connected to one end of a WDM coupler 5 through an optical amplifier 2 that amplifies and distributes the signal output from the video system 1.

一方、上位網３に接続されたＯＬＴ４も、ＷＤＭカプラ５の他端に接続され、光ファイバ６と光スプリッタ７を介して、別のＷＤＭカプラ８に接続される。
ＷＤＭカプラ８の加入者側の一端には、光―電気変換した後ＦＭ一括復調する受信器であるＶ−ＯＮＵ９が接続され、Ｖ−ＯＮＵ９の加入者側にはＴＶ１１が接続される。ＷＤＭカプラ８の加入者側の他端には、データ送受信用ＯＮＵ１０が接続されて、ＰＣ１２につながっている。 On the other hand, the OLT 4 connected to the higher level network 3 is also connected to the other end of the WDM coupler 5 and connected to another WDM coupler 8 via the optical fiber 6 and the optical splitter 7.
One end of the WDM coupler 8 on the subscriber side is connected to a V-ONU 9 which is a receiver that performs FM-to-electrical conversion after optical-electrical conversion, and a TV 11 is connected to the subscriber side of the V-ONU 9. A data transmission / reception ONU 10 is connected to the other end of the WDM coupler 8 on the subscriber side and is connected to the PC 12.

使用波長としては、例えば、電話局から家庭へのデータ伝送に１４９０ｎｍの波長を用い、家庭から電話局へのデータ伝送に１３１０ｎｍの波長を用い、上述の映像信号を１５５０ｎｍの波長の光信号で伝送して波長多重する。これにより、既に設置された光ファイバを用いてテレビ向けのアナログ信号を伝送することが可能となっている。   For example, a wavelength of 1490 nm is used for data transmission from the telephone office to the home, a wavelength of 1310 nm is used for data transmission from the home to the telephone office, and the above video signal is transmitted as an optical signal having a wavelength of 1550 nm. Wavelength multiplexing. Thereby, it is possible to transmit an analog signal for television using an already installed optical fiber.

図２は、ＦＭ一括変調方式の図を示す。
通常、テレビプログラムはテレビチャネル毎に異なる周波数の搬送波を用いてアナログ変調され、変調後の信号は、例えば６ＭＨｚ等の周波数間隔で周波数多重されて送信される。この信号をさらに電気信号から光信号に変換し、ＳＣＭ（Ｓｕｂ Ｃａｒｒｉｅｒ Ｍｕｌｔｉｐｌｅｘｉｎｇ）方式の信号を生成する。この信号の周波数スペクトルを図２（ａ）に示す。 FIG. 2 shows a diagram of the FM batch modulation scheme.
Normally, a television program is analog-modulated using a carrier wave having a different frequency for each television channel, and the modulated signal is frequency-multiplexed at a frequency interval such as 6 MHz and transmitted. This signal is further converted from an electric signal to an optical signal to generate a signal of an SCM (Sub Carrier Multiplexing) method. The frequency spectrum of this signal is shown in FIG.

上述のように品質の良好な映像信号は、例えば、５０ｄＢ程度のＣ／Ｎ（キャリア／ノイズ比）を保ったまま伝送される必要があるが、光ファイバ伝送においてはファイバの接続点による光反射などの影響で、上記Ｃ／Ｎが３０ｄＢ程度まで悪化してしまうことがある。この状況でも映像信号の品質を保つため、振幅歪に強い耐性を持つＦＭ変調技術を応用し、上記ＳＣＭ信号を一括してＦＭ変調して伝送する。例えば、数１００チャネルすなわち数１００本のサブキャリアを多重した映像信号は１ＧＨｚないしそれ以上の帯域を持つ。したがって、ＦＭ一括変調のキャリア周波数は数ＧＨｚという高い周波数を用いる必要がある。ＦＭ一括変調後の信号の周波数スペクトルを図２（ｂ）に示す。
図１にて説明したＶ−ＯＮＵ９にて復調されたＦＭ一括復調後の信号の周波数スペクトルを図２（ｃ）に示す。信号歪のある条件で伝送されたＦＭ一括変調信号を復調すると、図に示すようにＦＭ一括変調キャリアが残留する。このレベルが残留キャリアレベルである。 As described above, a video signal with good quality needs to be transmitted while maintaining a C / N (carrier / noise ratio) of, for example, about 50 dB. In optical fiber transmission, light reflection at the connection point of the fiber is required. For example, the C / N may be deteriorated to about 30 dB. In this situation, in order to maintain the quality of the video signal, an FM modulation technique having high resistance to amplitude distortion is applied, and the SCM signals are FM-modulated and transmitted together. For example, a video signal obtained by multiplexing several hundred channels, that is, several hundred subcarriers, has a band of 1 GHz or more. Therefore, it is necessary to use a high frequency of several GHz as the carrier frequency for FM batch modulation. The frequency spectrum of the signal after FM batch modulation is shown in FIG.
FIG. 2C shows the frequency spectrum of the signal after FM batch demodulation demodulated by the V-ONU 9 described in FIG. When the FM batch modulation signal transmitted under a condition with signal distortion is demodulated, the FM batch modulation carrier remains as shown in the figure. This level is the residual carrier level.

２．Ｖ−ＯＮＵの構成（１）
図３は、本発明の実施の形態のＶ−ＯＮＵ９の構成図を示す。
Ｖ−ＯＮＵ９は、光―電気変換するＰＤ（Ｐｈｏｔｏ Ｄｉｏｄｅ）３１と、ＰＤ３１の出力電流を電圧に変換するＴＩＡ（Ｔｒａｎｓ Ｉｍｐｅｄａｎｃｅ Ａｍｐｌｉｆｉｅｒ）３２を介して、後に説明する入力振幅に依存する利得を有する差動増幅器３３を介してＦＭ一括復調回路３４に接続され、ＦＭ一括復調回路３４の出力はＴＶ１１に接続される。ＦＭ一括復調回路３４は、遅延回路４１、ＥＸ−ＯＲ回路４２、ローパスフィルタ４３を備える。また、ＦＭ一括復調回路３４の出力には信号幅歪検出部３５、続いて補正しきい値生成部３６が接続され、補正しきい値生成部３６の出力（補正しきい値）が差動増幅器３３の他の入力端子に接続される。 2. Configuration of V-ONU (1)
FIG. 3 shows a configuration diagram of the V-ONU 9 according to the embodiment of the present invention.
The V-ONU 9 is a difference having a gain depending on an input amplitude, which will be described later, via a PD (Photo Diode) 31 that performs photoelectric conversion and a TIA (Trans Impedance Amplifier) 32 that converts an output current of the PD 31 into a voltage. The FM batch demodulation circuit 34 is connected to the TV 11 via the dynamic amplifier 33, and the output of the FM batch demodulation circuit 34 is connected to the TV 11. The FM batch demodulation circuit 34 includes a delay circuit 41, an EX-OR circuit 42, and a low-pass filter 43. The output of the FM collective demodulation circuit 34 is connected to a signal width distortion detector 35 and subsequently a correction threshold value generator 36. The output (correction threshold value) of the correction threshold value generator 36 is a differential amplifier. 33 connected to other input terminals.

信号幅歪を被ったＦＭ一括変調信号をＦＭ復調するとＦＭ一括変調キャリアが残留することが知られている。残留するキャリアレベルの大きさは信号幅歪が大きいほど大きい。信号幅歪検出部３５は、ＦＭ一括変調のキャリア周波数のみを通過させるバンドパスフィルタ４４とその出力のレベルを測定する部分４５から構成することができる。   It is known that when an FM batch modulation signal subjected to signal width distortion is FM demodulated, an FM batch modulation carrier remains. The magnitude of the remaining carrier level increases as the signal width distortion increases. The signal width distortion detection unit 35 can be composed of a bandpass filter 44 that allows only FM carrier frequency to pass through and a portion 45 that measures the output level thereof.

図４は、本発明の実施の形態の増幅器の特性を示す。
図４（ａ）に示すように本実施の形態の差動増幅器３３の利得は、しきい値電圧近傍では高い利得を、しきい値より離れるほど低い利得を持たせておく。差動増幅器３３は、しきい値に近い部分の信号を大きな利得で増幅し、しきい値から離れた部分の信号を小さな利得で増幅する。この特性を図４（ｂ）に示す。したがって、入力信号としきい値が交わる付近の信号幅を強調して再生するように信号を歪ませる効果が得られる。 FIG. 4 shows the characteristics of the amplifier according to the embodiment of the present invention.
As shown in FIG. 4A, the gain of the differential amplifier 33 according to the present embodiment has a high gain in the vicinity of the threshold voltage and a lower gain as the distance from the threshold increases. The differential amplifier 33 amplifies a signal near the threshold with a large gain and amplifies a signal far from the threshold with a small gain. This characteristic is shown in FIG. Therefore, it is possible to obtain an effect of distorting the signal so that the signal width near the intersection of the input signal and the threshold is emphasized and reproduced.

図５から図７は、本発明の実施の形態の増幅器のしきい値と出力信号の関係を示す。
図５に示すように、たとえば正弦波状の信号を本増幅器に入力する時、正方向振幅の信号と負方向振幅の信号が同じ幅である正弦波状の信号の中心値にしきい値が一致していれば、増幅後の信号は振幅の両端での振幅歪が発生する場合があるものの正方向の信号と負方向の信号が同じ幅に保たれた出力が得られる。この場合、しきい値よりプラス方向の成分とマイナス方向の成分が同程度となり、キャリアレベルが、理想的な無歪条件ではゼロとなる。図６に示すように、しきい値を下げると正方向振幅の信号に比べて負方向振幅の信号がより増幅されるため、正方向の信号の幅は広く、負方向の信号の幅が狭い出力が得られる。これは、入力信号の信号幅が広くなる方向に歪を与えたことに相当する。図７に示すように、逆にしきい値を上げると負方向振幅の信号に比べて正方向振幅の信号がより増幅されるため、正方向の信号の幅は狭く、負方向の信号の幅が広い出力が得られる。これは、入力信号の信号幅が狭くなる方向に歪を与えたことに相当する。したがって、ＦＭ一括変換信号の信号幅歪を測定した後、この作用を用いて、信号幅歪に応じて上記しきい値電圧を増減させることで、信号幅歪を減少させた信号を得ることが可能となる。 5 to 7 show the relationship between the threshold value and the output signal of the amplifier according to the embodiment of the present invention.
As shown in FIG. 5, for example, when a sine wave signal is input to this amplifier, the threshold value coincides with the center value of the sine wave signal having the same width as the positive amplitude signal and the negative amplitude signal. Then, although the amplified signal may cause amplitude distortion at both ends of the amplitude, an output in which the positive signal and the negative signal are kept in the same width can be obtained. In this case, the components in the positive direction and the components in the negative direction are approximately the same as the threshold value, and the carrier level is zero under an ideal no-distortion condition. As shown in FIG. 6, when the threshold value is lowered, the negative amplitude signal is amplified more than the positive amplitude signal. Therefore, the positive signal width is wide and the negative signal width is narrow. Output is obtained. This corresponds to applying distortion in the direction in which the signal width of the input signal becomes wider. As shown in FIG. 7, when the threshold value is raised, the positive amplitude signal is amplified more than the negative amplitude signal, so that the positive signal width is narrow and the negative signal width is small. A wide output can be obtained. This corresponds to applying distortion in the direction in which the signal width of the input signal becomes narrower. Therefore, after measuring the signal width distortion of the FM batch conversion signal, this signal can be used to increase or decrease the threshold voltage according to the signal width distortion to obtain a signal with reduced signal width distortion. It becomes possible.

３．フローチャート

３−１．実施の形態１
図８は、本発明の実施の形態１のフローチャートを示す。このフローチャートは、補正しきい値生成部３６が実行するフローチャートである。
図９、１０は、本発明の実施の形態の増幅器のしきい値と入出力信号の関係を示す。
図１１は信号幅歪と加えるべきしきい値の関係をしめす。しきい値の調整は、以下の手順を踏んで行う。 3. flowchart

3-1. Embodiment 1
FIG. 8 shows a flowchart of the first embodiment of the present invention. This flowchart is a flowchart executed by the correction threshold value generator 36.
9 and 10 show the relationship between the threshold value and the input / output signal of the amplifier according to the embodiment of the present invention.
FIG. 11 shows the relationship between the signal width distortion and the threshold value to be added. The threshold value is adjusted according to the following procedure.

まず、補正しきい値生成部３６は、初期状態にてしきい値を中央値に設定しておく。信号幅歪検出部３５は、ＦＭ一括復調回路３４から信号を受信すると、キャリア周波数に合わせたバンドパスフィルタ４４およびレベル検出器４５を用いてＦＭ一括キャリアレベルを出力するので、補正しきい値生成部３６は、その出力をモニタしておく（１０１）。補正しきい値生成部３６は、続いてキャリアレベルが、所定の許容値以下であるか否かを判定する（１０２）。無歪条件ではゼロとなるべきキャリアレベルが、所定の値よりも低ければ信号幅歪は十分小さく、映像品質が高い状態である。キャリアレベルが所定の値よりも高ければ、許容以上の信号幅歪が発生しているとみなせる。信号幅歪が発生している例として、図９に示すように信号幅歪が負方向の信号（プラス方向の成分が細い信号）が入力された場合で説明する。まず、補正しきい値生成部３６は、増幅器しきい値を減少方向にあらかじめ定めた１単位の電圧だけ変化させ（１０３）、予め定められたしきい値であるしきい値１に設定し、キャリアレベルの増分Ｖｃ−を信号幅歪検出部３５の出力によりモニタして、内部メモリ等に記憶する（１０４）。この結果、もしキャリアレベルが減少すれば、負方向に存在した信号幅歪に正の方向の信号幅歪が加えられて、出力波形１に示すように最終的な歪が減少した可能性が高いと考えられる。続いて、補正しきい値生成部３６は、増幅器しきい値を増加方向にあらかじめ定めた１単位の電圧だけ変化させ（１０５）、しきい値２に設定し、キャリアレベルの増分Ｖｃ＋をモニタして、内部メモリ等に記憶する（１０６）。もしキャリアレベルが増加すれば、やはり負方向に存在した信号幅歪に、負方向の信号幅歪がさらに加えられて出力波形２に示すように最終的な歪が増加した可能性が高いと考えられる。以後、補正しきい値生成部３６は、Ｖｃ＋＞０かつＶｃ−＜０であれば（１０７）、しきい値を１単位の電圧だけ減少させて（１０８）、キャリアレベルが、所定の許容値以下になるまで上記処理を繰り返す。また、図１０に示すように信号幅歪が正方向の信号（プラス方向の成分が太い信号）が入力された場合には同様の原理及び処理でＶｃ＋＜０かつＶｃ−＞０となるが（１０９）、その場合は逆にしきい値を１単位の電圧だけ増加させて（１１０）、キャリアレベルが、所定の許容値以下になるまで上記処理を繰り返す。こうして、しきい値の増減の方向とキャリアレベルの増減の相関がとれれば、キャリアレベルが所定の値より小さくなるまでしきい値を変化させれば信号幅歪を補正することが可能となる。   First, the correction threshold value generator 36 sets the threshold value to the median value in the initial state. When the signal width distortion detection unit 35 receives a signal from the FM batch demodulation circuit 34, the signal width distortion detection unit 35 outputs the FM batch carrier level using the bandpass filter 44 and the level detector 45 matched to the carrier frequency. The unit 36 monitors the output (101). Subsequently, the correction threshold value generator 36 determines whether the carrier level is equal to or lower than a predetermined allowable value (102). If the carrier level that should be zero under the no distortion condition is lower than a predetermined value, the signal width distortion is sufficiently small and the video quality is high. If the carrier level is higher than a predetermined value, it can be considered that signal width distortion more than allowable is generated. As an example in which the signal width distortion occurs, a case where a signal having a negative signal width distortion (a signal having a thin component in the positive direction) is input as shown in FIG. First, the correction threshold value generator 36 changes the amplifier threshold value by a predetermined unit voltage in a decreasing direction (103) and sets the threshold value to a threshold value 1 which is a predetermined threshold value. The carrier level increment Vc− is monitored by the output of the signal width distortion detector 35 and stored in the internal memory or the like (104). As a result, if the carrier level is decreased, the signal width distortion in the positive direction is added to the signal width distortion existing in the negative direction, and it is highly possible that the final distortion is decreased as shown in the output waveform 1. it is conceivable that. Subsequently, the correction threshold value generator 36 changes the amplifier threshold value by a predetermined unit voltage in the increasing direction (105), sets the threshold value to 2 and monitors the carrier level increment Vc +. And stored in the internal memory (106). If the carrier level increases, it is highly likely that the final distortion has increased as shown in the output waveform 2 by further adding the negative signal width distortion to the negative signal width distortion. It is done. Thereafter, if Vc +> 0 and Vc− <0 (107), the correction threshold value generation unit 36 decreases the threshold value by one unit voltage (108), and the carrier level becomes a predetermined allowable value. Repeat the above process until: Also, as shown in FIG. 10, when a signal with a positive signal width distortion (a signal with a thick positive component) is input, Vc + <0 and Vc−> 0 with the same principle and processing ( 109), in that case, the threshold value is increased by one unit voltage (110), and the above process is repeated until the carrier level becomes a predetermined allowable value or less. Thus, if the increase / decrease direction of the threshold is correlated with the increase / decrease of the carrier level, the signal width distortion can be corrected by changing the threshold until the carrier level becomes smaller than a predetermined value.

ただし、信号幅歪が大きい場合、１単位のしきい値電圧の変化ではキャリアレベルの変化が検出できない可能性がある。あるいは雑音により、しきい値を増加させても減少させてもキャリアレベルが増加する場合、しきい値を増加させても減少させてもキャリアレベルが減少する場合等も考えられる。この場合、上記しきい値電圧を２単位又は所定の複数単位に増加させ（１１１）同じ処理を繰り返すことにより、いずれかの電圧でしきい値の増減の方向とキャリアレベルの増減の相関がとれるようになる。   However, when the signal width distortion is large, a change in carrier level may not be detected by a change in threshold voltage of one unit. Alternatively, the carrier level may be increased by increasing or decreasing the threshold value due to noise, or the carrier level may be decreased by increasing or decreasing the threshold value. In this case, the threshold voltage is increased to 2 units or a predetermined plurality of units (111), and the same process is repeated to correlate the direction of increase / decrease of the threshold and the increase / decrease of the carrier level at any voltage. It becomes like this.

以上より求めたしきい値とキャリアレベルの増減の相関より、信号幅歪としきい値に加えるべき変更量の関係を求めると、図１１に実線で示す通りとなる。例えば、図中ａ点で示したように、信号幅歪が細い（負方向）の場合は、しきい値に加えるべき変更量は下げる。図中ｂ点で示したように、信号幅歪が太い（正方向）の場合は、しきい値に加えるべき変更量は上げる。また、図中ｃ点で示したように、信号幅歪が細い（負方向）の場合且つａ点より細い場合は、しきい値に加えるべき変更量は、ａ点の場合より一層大幅に下げることになる。   The relationship between the signal width distortion and the amount of change to be added to the threshold value is obtained from the correlation between the threshold value obtained and the carrier level increase / decrease as described above, as shown by a solid line in FIG. For example, as shown by point a in the figure, when the signal width distortion is thin (in the negative direction), the amount of change to be added to the threshold value is lowered. As indicated by point b in the figure, when the signal width distortion is large (in the positive direction), the amount of change to be added to the threshold value is increased. Further, as shown by the point c in the figure, when the signal width distortion is thin (in the negative direction) and smaller than the point a, the amount of change to be added to the threshold value is much lower than that at the point a. It will be.

３−２．実施の形態２
図１２は、本発明の実施の形態２のフローチャートを示す。このフローチャートは、補正しきい値生成部３６が実行するフローチャートである。
実施の形態２は、ステップ１１２が、実施の形態１のステップ１０７、１０９、１１１と異なる。実施の形態２では、補正しきい値生成部３６は、しきい値の増減の方向とキャリアレベルの増減の相関をとる手順は、しきい値を増加させた時のＦＭ一括キャリアレベルの変化量としきい値を減少させた時のＦＭ一括キャリアレベルの変化量の差分量の正負を用いて、信号幅歪方向の正負としきい値の増減量の相関を決定する（１１２）。他の処理は図８の動作と同じである。この実施の形態２では、しきい値と残留キャリアレベルの相関の判定処理が簡略化され、収束までの時間が短くできる利点がある。 3-2. Embodiment 2
FIG. 12 shows a flowchart of the second embodiment of the present invention. This flowchart is a flowchart executed by the correction threshold value generator 36.
In the second embodiment, step 112 is different from steps 107, 109, and 111 in the first embodiment. In the second embodiment, the correction threshold value generation unit 36 performs the procedure of correlating the direction of increase / decrease of the threshold value and the increase / decrease of the carrier level by changing the FM batch carrier level when the threshold value is increased. The correlation between the positive / negative of the signal width distortion direction and the increase / decrease amount of the threshold value is determined using the positive / negative of the difference amount of the change amount of the FM collective carrier level when the threshold value is decreased (112). Other processing is the same as the operation of FIG. The second embodiment has an advantage that the process for determining the correlation between the threshold value and the residual carrier level is simplified, and the time until convergence can be shortened.

３−３．実施の形態３
図１３は、本発明の実施の形態３のフローチャートを示す。このフローチャートは、補正しきい値生成部３６が実行するフローチャートである。
図１７に、本発明の実施の形態３のＶ−ＯＮＵの構成図を示す。この実施の形態３では、補正しきい値生成部３６は、その内部（又は外部）にしきい値制御テーブル３７をさらに備える。 3-3. Embodiment 3
FIG. 13 shows a flowchart of the third embodiment of the present invention. This flowchart is a flowchart executed by the correction threshold value generator 36.
FIG. 17 shows a configuration diagram of a V-ONU according to the third embodiment of the present invention. In the third embodiment, the correction threshold value generator 36 further includes a threshold value control table 37 inside (or outside).

図１５に、しきい値制御テーブルの説明図を示す。
実施の形態３は、ステップ１１３が実施の形態１に追加されたものである。実施の形態３では、補正しきい値生成部３６は、しきい値を変化させる手順は、信号歪検出部３５から入力されたＦＭ一括キャリアレベルの大きさに基づいて、しきい値の変化量を毎回又は所定回毎に変えることができる。具体的には、補正しきい値生成部３６は、図１５に示すキャリアレベルが大きい程、しきい値の増分も大きいしきい値制御テーブルを参照し（１１３）、ステップ１０３で、図８と同様に、しきい値を変化させる処理を行う。この手順は、より速く少ないしきい値調整回数でしきい値の調整を収束させるために有効である。 FIG. 15 is an explanatory diagram of the threshold control table.
In the third embodiment, step 113 is added to the first embodiment. In the third embodiment, the correction threshold value generating unit 36 changes the threshold value based on the FM collective carrier level input from the signal distortion detecting unit 35. Can be changed every time or every predetermined time. Specifically, the correction threshold value generator 36 refers to the threshold value control table in which the threshold value increment increases as the carrier level shown in FIG. 15 increases (113). Similarly, processing for changing the threshold value is performed. This procedure is effective to converge the threshold adjustment faster and with fewer threshold adjustments.

３−４．実施の形態４
図１４は、本発明の実施の形態４のフローチャートを示す。このフローチャートは、補正しきい値生成部３６が実行するフローチャートである。Ｖ−ＯＮＵの構成は、実施の形態３と同様である。
実施の形態４は、ステップ１１３が実施の形態２に追加されたものである。実施の形態４では、補正しきい値生成部３６は、実施の形態３と同様にFM一括キャリアレベルの大きさに基づいてしきい値制御テーブルを参照し（１１３）、図１２と同様の処理を行う。この手順は、より速く少ないしきい値調整回数でしきい値の調整を収束させるために有効である。 3-4. Embodiment 4
FIG. 14 shows a flowchart of the fourth embodiment of the present invention. This flowchart is a flowchart executed by the correction threshold value generator 36. The configuration of the V-ONU is the same as that of the third embodiment.
In the fourth embodiment, step 113 is added to the second embodiment. In the fourth embodiment, the correction threshold value generation unit 36 refers to the threshold value control table based on the FM collective carrier level as in the third embodiment (113), and performs the same processing as in FIG. I do. This procedure is effective to converge the threshold adjustment faster and with fewer threshold adjustments.

４．Ｖ−ＯＮＵの構成（２）
図１６は、本発明の他の実施の形態でのＶ−ＯＮＵ９の構成図を示す。
具体的には、図１６におけるパルス幅歪み補正回路３７、残留キャリア成分抽出回路３８、キャリアリーク量判定回路３９が、図３における増幅器３３、信号歪検出部３５、補正しきい値生成部３６と代わった点が異なる。このＶ−ＯＮＵ９は、ＦＭ一括復調回路３４の出力に接続された残留キャリア成分抽出回路３８は、バンドパスフィルタ４４と抵抗４５とコンデンサ４６を用いて構成されることにより、検出レベルを保持する簡易な構成であり、また、キャリアリーク量判定回路３９は所定の比較しきい値電圧４７と比較器４８から構成されるやはり簡易な構成である。比較器４８から出力される補正信号でコンパレータ５０のしきい値電圧４９を制御する。コンパレータ５０は、図３の差動増幅器と同様の構成及び特性とすることができる。
本実施の形態の適用範囲は、特に、信号幅歪の主要因が光伝送中の非線形効果によるパルス圧縮である場合である。信号幅歪はパルスが細る方向に決まっているので、第１から第４の実施の形態に示したように、しきい値の変化方向と残留キャリアレベルの増減の相関をとる必要がなく、このような簡易な構成による調整を可能としている。 4). Configuration of V-ONU (2)
FIG. 16 shows a configuration diagram of the V-ONU 9 according to another embodiment of the present invention.
Specifically, the pulse width distortion correction circuit 37, the residual carrier component extraction circuit 38, and the carrier leak amount determination circuit 39 in FIG. 16 are connected to the amplifier 33, the signal distortion detection unit 35, and the correction threshold value generation unit 36 in FIG. The point of change is different. In this V-ONU 9, the residual carrier component extraction circuit 38 connected to the output of the FM collective demodulation circuit 34 is configured by using a band pass filter 44, a resistor 45, and a capacitor 46, so that the detection level can be easily maintained. The carrier leak amount determination circuit 39 is also a simple configuration including a predetermined comparison threshold voltage 47 and a comparator 48. The threshold voltage 49 of the comparator 50 is controlled by the correction signal output from the comparator 48. The comparator 50 can have the same configuration and characteristics as the differential amplifier of FIG.
The application range of the present embodiment is particularly the case where the main factor of signal width distortion is pulse compression due to nonlinear effects during optical transmission. Since the signal width distortion is determined in the direction in which the pulse narrows, as shown in the first to fourth embodiments, there is no need to correlate the change direction of the threshold value with the increase or decrease in the residual carrier level. Adjustment with such a simple configuration is possible.

本発明はＰＯＮを用いたシステムの他にも、ＦＭ一括変換方式を用いたシステムに幅広く適用することができる。   The present invention can be widely applied to systems using the FM batch conversion method in addition to systems using PON.

１・・・映像送信システム、２・・・光アンプ、３・・・上位網、４・・・ＯＬＴ、５・・・ＷＤＭカプラ、６・・・光ファイバ、７・・・光スプリッタ、８・・・ＷＤＭカプラ、９・・・Ｖ−ＯＮＵ、１０・・・ＯＮＵ、１１・・・ＴＶ、１２・・・ＰＣ、３１・・・ＰＤ、３２・・・ＴＩＡ、３３・・・増幅器、３４・・・ＦＭ復調回路、３５・・・信号歪検出部、３６・・・補正しきい値生成部 DESCRIPTION OF SYMBOLS 1 ... Video transmission system, 2 ... Optical amplifier, 3 ... Upper network, 4 ... OLT, 5 ... WDM coupler, 6 ... Optical fiber, 7 ... Optical splitter, 8 ... WDM coupler, 9 ... V-ONU, 10 ... ONU, 11 ... TV, 12 ... PC, 31 ... PD, 32 ... TIA, 33 ... amplifier, 34... FM demodulation circuit, 35... Signal distortion detector, 36.

Claims (10)

複数の映像信号を異なる搬送波で変調して周波数多重及びＦＭ一括変調して、光信号として送信する送信装置と、上記送信装置から出力された光信号を伝送する光ファイバ網と、上記光ファイバ網から光信号を受信してひとつ又は複数の映像信号に復調する受信装置とを備えた映像伝送システムにおける、映像信号受信装置であって、
上記光ファイバ網からの光信号を受信して光―電気変換する光−電気変換部と、
一方の入力端子を上記光―電気変換部の出力に接続され、他方の入力端子にしきい値が入力され、しきい値電圧近傍では高い利得を、しきい値より離れるほど低い利得を持つような、入力信号の振幅に依存した利得を持つ差動増幅器と、
上記差動増幅器からの出力をＦＭ一括復調するＦＭ一括復調部と、
上記ＦＭ一括復調部の出力から、ＦＭ一括復調の信号幅歪が大きいほど大きい値を示すＦＭ一括変調のキャリア周波数の、ＦＭ一括キャリアレベルを検出する信号幅歪検出部と、
上記信号幅歪検出部の出力から、信号幅歪に応じた補正しきい値を生成し、該補正しきい値を上記差動増幅器の他方の入力端子に出力する補正しきい値生成部と、
を備え、

上記補正しきい値生成部は、
初期状態にてしきい値を中央値に設定してＦＭ一括キャリアレベルをモニタし、
しきい値を減少方向に変化させてＦＭ一括キャリアレベルの第１の変化量を求め、
しきい値を増加方向に変化させてＦＭ一括キャリアレベルの第２の変化量を求め、
上記第１及び第２の変化量に基づきしきい値を減少又は増加させることにより、ＦＭ一括キャリアレベルが予め定めた許容値以下になるようにしきい値の増加又は減少の変化方向と変化量とを調整し、
しきい値を減少させることで、プラス方向の成分の信号幅が時間方向に細くなる負方向の信号幅歪を減少させ、又は、しきい値を増加させることで、プラス方向の成分の信号幅が時間方向に太くなる正方向の信号幅歪を減少させるための、補正しきい値を求めるようにした、
前記映像信号受信装置。 A transmission apparatus that modulates a plurality of video signals with different carrier waves, performs frequency multiplexing and FM batch modulation, and transmits them as an optical signal; an optical fiber network that transmits an optical signal output from the transmission apparatus; and the optical fiber network A video signal receiving device in a video transmission system comprising a receiving device that receives an optical signal from and demodulates into one or a plurality of video signals,
An optical-electrical converter that receives an optical signal from the optical fiber network and performs optical-electrical conversion;
One input terminal is connected to the output of the opto-electric converter, the other input terminal has a threshold value input, and a high gain is obtained in the vicinity of the threshold voltage, and a lower gain is obtained as the distance from the threshold value increases. A differential amplifier having a gain depending on the amplitude of the input signal;
An FM batch demodulator for FM demodulating the output from the differential amplifier;
A signal width distortion detection unit for detecting an FM collective carrier level of an FM collective modulation carrier frequency that indicates a larger value as the signal width distortion of the FM collective demodulation increases from the output of the FM collective demodulation unit;
A correction threshold value generating unit that generates a correction threshold value according to the signal width distortion from the output of the signal width distortion detection unit, and outputs the correction threshold value to the other input terminal of the differential amplifier;
With

The correction threshold value generator is
In the initial state, set the threshold value to the median value and monitor the FM batch carrier level.
The threshold value is changed in the decreasing direction to obtain the first change amount of the FM collective carrier level,
The threshold value is changed in the increasing direction to obtain the second change amount of the FM collective carrier level,
By decreasing or increasing the threshold based on the first and second change amounts, the change direction and change amount of the threshold increase or decrease so that the FM collective carrier level is equal to or less than a predetermined allowable value. Adjust
Decreasing the threshold value reduces the signal width distortion in the negative direction where the signal width of the positive direction component becomes narrower in the time direction, or increasing the threshold value increases the signal width of the positive direction component. The correction threshold value is calculated to reduce the signal width distortion in the positive direction that becomes thicker in the time direction.
The video signal receiving device. 上記信号幅歪検出部は、
ＦＭ一括変調のキャリア周波数のみを通過させるバントパスフィルタと、
該バンドパスフィルタの出力のレベルを測定するレベル検出部と
を備えたことを特徴とする請求項１に記載の映像信号受信装置。 The signal width distortion detector
A band pass filter that passes only the carrier frequency of FM batch modulation;
The video signal receiving apparatus according to claim 1, further comprising: a level detecting unit that measures an output level of the band pass filter. 上記補正しきい値生成部は、
上記しきい値を増加方向に変化させた時に上記ＦＭ一括キャリアレベルが増加し且つ上記しきい値を減少方向に変化させた時に上記ＦＭ一括キャリアレベルが減少する第１条件、
又は、
上記しきい値を増加方向に変化させた時に上記ＦＭ一括キャリアレベルが減少し且つ上記しきい値を減少方向に変化させた時に上記ＦＭ一括キャリアレベルが増加する第２条件、
のいずれかの条件を満たすまで、しきい値の増減幅を所定のしきい値増分単位ずつ増加させ、
上記第１条件を満たすとき、しきい値を減少させて所定の許容値以下になるまでしきい値を所定のしきい値増分単位ずつ調整することにより、補正しきい値を求め、一方、上記第２条件を満たすとき、しきい値を増加させて所定の許容値以下になるまでしきい値を所定のしきい値増分単位ずつ調整することにより、補正しきい値を求めることを特徴とする請求項１に記載の映像信号受信装置。 The correction threshold value generator is
A first condition in which the FM collective carrier level increases when the threshold value is changed in an increasing direction and the FM collective carrier level decreases when the threshold value is changed in a decreasing direction;
Or
A second condition in which the FM collective carrier level decreases when the threshold value is changed in the increasing direction and the FM collective carrier level increases when the threshold value is changed in the decreasing direction;
Increase or decrease the threshold increment by a predetermined threshold increment until one of the conditions is met,
When the first condition is satisfied, a correction threshold value is obtained by decreasing the threshold value and adjusting the threshold value by a predetermined threshold increment unit until the threshold value is less than or equal to a predetermined allowable value. When the second condition is satisfied, a correction threshold value is obtained by increasing the threshold value and adjusting the threshold value by a predetermined threshold increment unit until the threshold value is not more than a predetermined allowable value. The video signal receiving apparatus according to claim 1. 前記補正しきい値生成部は、
前記第１条件又は前記第２条件が満たされないとき、しきい値増分単位を増加させることを特徴とする請求項３に記載の映像信号受信装置。 The correction threshold value generation unit
4. The video signal receiving apparatus according to claim 3, wherein when the first condition or the second condition is not satisfied, a threshold increment unit is increased. 前記ＦＭ一括キャリアレベルが大きい程、しきい値増分が大きくなるようなしきい値増分単位を記憶した、しきい値制御テーブルをさらに備え、
上記補正しきい値生成部は、
上記しきい値を変化させるときに、上記しきい値制御テーブルを参照し、上記ＦＭ一括キャリアレベルの大きさに基づいて、上記しきい値の変化量を定めることを特徴とする請求項３に記載の映像信号受信装置。 A threshold control table storing a threshold increment unit such that the threshold increment increases as the FM collective carrier level increases;
The correction threshold value generator is
4. The threshold value change amount is determined based on the FM batch carrier level by referring to the threshold value control table when the threshold value is changed. The video signal receiving apparatus described. 上記補正しきい値生成部は、
上記しきい値を減少方向に変化させた時の上記ＦＭ一括キャリアレベルの第１の変化量と、上記しきい値を増加方向に変化させた時の上記ＦＭ一括キャリアレベルの第２の変化量との差分量を求め、
第２の変化量が第１の変化量より大きければ、しきい値を減少させて所定の許容値以下になるまでしきい値を調整することにより、補正しきい値を求め、一方、第１の変化量が第２の変化量より大きければ、しきい値を増加させて所定の許容値以下になるまでしきい値を調整することにより、補正しきい値を求めること
を特徴とする請求項４に記載の映像信号受信装置。 The correction threshold value generator is
A first change amount of the FM collective carrier level when the threshold value is changed in a decreasing direction, and a second change amount of the FM collective carrier level when the threshold value is changed in an increasing direction. The amount of difference between
If the second change amount is larger than the first change amount, the correction threshold value is obtained by adjusting the threshold value until the threshold value is decreased to be equal to or less than a predetermined allowable value, while the first change amount is obtained. The correction threshold value is obtained by adjusting the threshold value until the threshold value is increased to be equal to or less than a predetermined allowable value if the change amount is larger than the second change amount. 5. The video signal receiving device according to 4. 前記ＦＭ一括キャリアレベルが大きい程、しきい値増分が大きくなるようなしきい値増分単位を記憶した、しきい値制御テーブルをさらに備え、
上記補正しきい値生成部は、
上記しきい値を変化させるときに、上記しきい値制御テーブルを参照し、上記ＦＭ一括キャリアレベルの大きさに基づいて、上記しきい値の変化量を定めることを特徴とする請求項６に記載の映像信号受信装置。 A threshold control table storing a threshold increment unit such that the threshold increment increases as the FM collective carrier level increases;
The correction threshold value generator is
7. The threshold value change amount is determined based on the FM collective carrier level with reference to the threshold value control table when the threshold value is changed. The video signal receiving apparatus described. 複数の映像信号を異なる搬送波で変調して周波数多重及びＦＭ一括変調して、光信号として送信する送信装置と、上記送信装置から出力された光信号を伝送する光ファイバ網と、上記光ファイバ網から光信号を受信してひとつ又は複数の映像信号に復調する受信装置とを備えた映像伝送システムにおける、映像信号受信装置であって、
上記光ファイバ網からの光信号を受信して光―電気変換する光−電気変換部と、
一方の入力端子を上記光―電気変換部の出力に接続され、他方の入力端子にしきい値が入力され、しきい値電圧近傍では高い利得を、しきい値より離れるほど低い利得を持つような、入力信号の振幅に依存した利得を持つ差動増幅器と、
上記差動増幅器からの出力をＦＭ一括復調するＦＭ一括復調部と、
残留キャリア成分を抽出するためのバンドパスフィルタと、前記バンドパスフィルタの出力を保持するための抵抗とコンデンサを含む回路とを備え、上記ＦＭ一括復調部の出力から、ＦＭ一括復調の信号幅歪が大きいほど大きい値を示すＦＭ一括変調のキャリア周波数の、ＦＭ一括キャリアレベルを抽出し保持する残留キャリア成分抽出回路と、
上記残留キャリア成分抽出回路の出力から、予め定められた比較しきい値電圧と比較する比較器を有し、補正信号を出力するキャリアリーク量判定回路と、
を備え、
上記キャリアリーク量判定回路の上記比較器から出力される補正信号で上記差動増幅器のしきい値電圧を調整することにより、主要因が光伝送中の非線形効果によるパルス圧縮による信号幅歪又はプラス方向の成分の信号幅が時間方向に細くなる負方向の信号幅歪を減少させるようにした、
前記映像信号受信装置。 A transmission apparatus that modulates a plurality of video signals with different carrier waves, performs frequency multiplexing and FM batch modulation, and transmits them as an optical signal; an optical fiber network that transmits an optical signal output from the transmission apparatus; and the optical fiber network A video signal receiving device in a video transmission system comprising a receiving device that receives an optical signal from and demodulates into one or a plurality of video signals,
An optical-electrical converter that receives an optical signal from the optical fiber network and performs optical-electrical conversion;
One input terminal is connected to the output of the opto-electric converter, the other input terminal has a threshold value input, and a high gain is obtained in the vicinity of the threshold voltage, and a lower gain is obtained as the distance from the threshold value increases. A differential amplifier having a gain depending on the amplitude of the input signal;
An FM batch demodulator for FM demodulating the output from the differential amplifier;
A band pass filter for extracting a residual carrier component; and a circuit including a resistor and a capacitor for holding the output of the band pass filter, and the signal width distortion of FM collective demodulation from the output of the FM collective demodulation unit A residual carrier component extraction circuit that extracts and holds an FM collective carrier level of an FM collective modulation carrier frequency that indicates a larger value as
A carrier leak amount determination circuit that has a comparator for comparing with a predetermined comparison threshold voltage from an output of the residual carrier component extraction circuit and outputs a correction signal;
With
By adjusting the threshold voltage of the differential amplifier with the correction signal output from the comparator of the carrier leak amount determination circuit, the main factor is signal width distortion due to non-linear effects during optical transmission, or plus The signal width distortion in the negative direction where the signal width of the direction component becomes narrower in the time direction has been reduced.
The video signal receiving device. 複数の映像信号を異なる搬送波で変調して周波数多重及びＦＭ一括変調して、光信号として送信する送信装置と、上記送信装置から出力された光信号を伝送する光ファイバ網と、上記光ファイバ網から光信号を受信してひとつ又は複数の映像信号に復調する受信装置とを備えた映像伝送システムにおいて、

上記送信装置は、
複数の映像信号をそれぞれ異なる周波数を持つ複数の搬送波を用いて変調する複数の変調部と、
上記複数の変調部によりそれぞれ複数の搬送波を用いて変調された複数の映像信号を周波数多重し、ＦＭ一括変調し、電気―光変換して送信するＦＭ一括変調部と、
を備え、

上記受信装置は、
上記光ファイバ網からの光信号を受信して光―電気変換する光−電気変換部と、
一方の入力端子を上記光―電気変換部の出力に接続され、他方の入力端子にしきい値が入力され、しきい値電圧近傍では高い利得を、しきい値より離れるほど低い利得を持つような、入力信号の振幅に依存した利得を持つ差動増幅器と、
上記差動増幅器からの出力をＦＭ一括復調するＦＭ一括復調部と、
上記ＦＭ一括復調部の出力から、ＦＭ一括復調の信号幅歪が大きいほど大きい値を示すＦＭ一括変調のキャリア周波数の、ＦＭ一括キャリアレベルを検出する信号幅歪検出部と、
上記信号幅歪検出部の出力から、信号幅歪に応じた補正しきい値を生成し、該補正しきい値を上記差動増幅器の他方の入力端子に出力する補正しきい値生成部と、
を備え、
上記補正しきい値生成部は、
初期状態にてしきい値を中央値に設定してＦＭ一括キャリアレベルをモニタし、
しきい値を減少方向に変化させてＦＭ一括キャリアレベルの第１の変化量を求め、
しきい値を増加方向に変化させてＦＭ一括キャリアレベルの第２の変化量を求め、
上記第１及び第２の変化量に基づきしきい値を減少又は増加させることにより、ＦＭ一括キャリアレベルが予め定めた許容値以下になるようにしきい値の増加又は減少の変化方向と変化量とを調整し、
しきい値を減少させることで、プラス方向の成分の信号幅が時間方向に細くなる負方向の信号幅歪を減少させ、又は、しきい値を増加させることで、プラス方向の成分の信号幅が時間方向に太くなる正方向の信号幅歪を減少させるための、補正しきい値を求めるようにした、
前記映像伝送システム。 A transmission apparatus that modulates a plurality of video signals with different carrier waves, performs frequency multiplexing and FM batch modulation, and transmits them as an optical signal; an optical fiber network that transmits an optical signal output from the transmission apparatus; and the optical fiber network In a video transmission system comprising a receiving device that receives an optical signal from and demodulates into one or a plurality of video signals,

The transmitter is
A plurality of modulation sections that modulate a plurality of video signals using a plurality of carrier waves having different frequencies, and
An FM batch modulation unit that frequency-multiplexes a plurality of video signals modulated by a plurality of carrier waves by the plurality of modulation units, performs FM batch modulation, performs electro-optical conversion, and transmits;
With

The receiving device is
An optical-electrical converter that receives an optical signal from the optical fiber network and performs optical-electrical conversion;
One input terminal is connected to the output of the opto-electric converter, the other input terminal has a threshold value input, and a high gain is obtained in the vicinity of the threshold voltage, and a lower gain is obtained as the distance from the threshold value increases. A differential amplifier having a gain depending on the amplitude of the input signal;
An FM batch demodulator for FM demodulating the output from the differential amplifier;
A signal width distortion detection unit for detecting an FM collective carrier level of an FM collective modulation carrier frequency that indicates a larger value as the signal width distortion of the FM collective demodulation increases from the output of the FM collective demodulation unit;
A correction threshold value generating unit that generates a correction threshold value according to the signal width distortion from the output of the signal width distortion detection unit, and outputs the correction threshold value to the other input terminal of the differential amplifier;
With
The correction threshold value generator is
In the initial state, set the threshold value to the median value and monitor the FM batch carrier level.
The threshold value is changed in the decreasing direction to obtain the first change amount of the FM collective carrier level,
The threshold value is changed in the increasing direction to obtain the second change amount of the FM collective carrier level,
By decreasing or increasing the threshold based on the first and second change amounts, the change direction and change amount of the threshold increase or decrease so that the FM collective carrier level is equal to or less than a predetermined allowable value. Adjust
Decreasing the threshold value reduces the signal width distortion in the negative direction where the signal width of the positive direction component becomes narrower in the time direction, or increasing the threshold value increases the signal width of the positive direction component. The correction threshold value is calculated to reduce the signal width distortion in the positive direction that becomes thicker in the time direction.
The video transmission system. 複数の映像信号を異なる搬送波で変調して周波数多重及びＦＭ一括変調して、光信号として送信する送信装置と、上記送信装置から出力された光信号を伝送する光ファイバ網と、上記光ファイバ網から光信号を受信してひとつ又は複数の映像信号に復調する受信装置とを備えた映像伝送システムにおいて、

上記送信装置は、
複数の映像信号をそれぞれ異なる周波数を持つ複数の搬送波を用いて変調する複数の変調部と、
上記複数の変調部によりそれぞれ複数の搬送波を用いて変調された複数の映像信号を周波数多重し、ＦＭ一括変調し、電気―光変換して送信するＦＭ一括変調部と、
を備え、

上記受信装置は、
上記光ファイバ網からの光信号を受信して光―電気変換する光−電気変換部と、
一方の入力端子を上記光―電気変換部の出力に接続され、他方の入力端子にしきい値が入力され、しきい値電圧近傍では高い利得を、しきい値より離れるほど低い利得を持つような、入力信号の振幅に依存した利得を持つ差動増幅器と、
上記差動増幅器からの出力をＦＭ一括復調するＦＭ一括復調部と、
残留キャリア成分を抽出するためのバンドパスフィルタと、前記バンドパスフィルタの出力を保持するための抵抗とコンデンサを含む回路とを備え、上記ＦＭ一括復調部の出力から、ＦＭ一括復調の信号幅歪が大きいほど大きい値を示すＦＭ一括変調のキャリア周波数の、ＦＭ一括キャリアレベルを抽出し保持する残留キャリア成分抽出回路と、
上記残留キャリア成分抽出回路の出力から、予め定められた比較しきい値電圧と比較する比較器を有し、補正信号を出力するキャリアリーク量判定回路と、
を備え、
上記キャリアリーク量判定回路の上記比較器から出力される補正信号で上記差動増幅器のしきい値電圧を調整することにより、主要因が光伝送中の非線形効果によるパルス圧縮による信号幅歪又はプラス方向の成分の信号幅が時間方向に細くなる負方向の信号幅歪を減少させるようにした、
前記映像伝送システム。 A transmission apparatus that modulates a plurality of video signals with different carrier waves, performs frequency multiplexing and FM batch modulation, and transmits them as an optical signal; an optical fiber network that transmits an optical signal output from the transmission apparatus; and the optical fiber network In a video transmission system comprising a receiving device that receives an optical signal from and demodulates into one or a plurality of video signals,

The transmitter is
A plurality of modulation sections that modulate a plurality of video signals using a plurality of carrier waves having different frequencies, and
An FM batch modulation unit that frequency-multiplexes a plurality of video signals modulated by a plurality of carrier waves by the plurality of modulation units, performs FM batch modulation, performs electro-optical conversion, and transmits;
With

The receiving device is
An optical-electrical converter that receives an optical signal from the optical fiber network and performs optical-electrical conversion;
One input terminal is connected to the output of the opto-electric converter, the other input terminal has a threshold value input, and a high gain is obtained in the vicinity of the threshold voltage, and a lower gain is obtained as the distance from the threshold value increases. A differential amplifier having a gain depending on the amplitude of the input signal;
An FM batch demodulator for FM demodulating the output from the differential amplifier;
A band pass filter for extracting a residual carrier component; and a circuit including a resistor and a capacitor for holding the output of the band pass filter, and the signal width distortion of FM collective demodulation from the output of the FM collective demodulation unit A residual carrier component extraction circuit that extracts and holds an FM collective carrier level of an FM collective modulation carrier frequency that indicates a larger value as
A carrier leak amount determination circuit that has a comparator for comparing with a predetermined comparison threshold voltage from an output of the residual carrier component extraction circuit and outputs a correction signal;
With
By adjusting the threshold voltage of the differential amplifier with the correction signal output from the comparator of the carrier leak amount determination circuit, the main factor is signal width distortion due to non-linear effects during optical transmission, or plus The signal width distortion in the negative direction where the signal width of the direction component becomes narrower in the time direction has been reduced.
The video transmission system.
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