JP3850566B2 - Video signal demodulation circuit - Google Patents

Description

【００３６】
となる。
【００３７】
また、色副搬送波生成回路６から上記数３で示す色副搬送波と位相が正確に一致した第２の色副搬送波が生成されている場合には、バースト期間での乗算器５の復調出力は、数１と数３とから、
【００３８】
【数６】
−cos(ω)×cos(ω)
となる。この数６で表わされる復調出力をカラーバースト信号の１サイクル分、即ち、０〜２πに渡って積分すると、
【００３９】
【数７】

【００４０】
となる。
【００４１】
以上より、色副搬送波生成回路６からの第１の色副搬送波が上記のように正しい位相を持つ場合には、積分回路１１が８〜１２サイクルのカラーバースト信号を含むバースト期間乗算器４からの復調信号を積分すると、その積分値は零となるものであって、位相制御回路９は、積分回路１１からの積分値Ｉ_Rに応じた制御パラメータＰ_B，Ｐ_Pを色副搬送波生成回路６に供給することにより、この積分値Ｉ_Rが零となるように、この色副搬送波生成回路６を制御して第１，第２の色副搬送波が上記の正しい位相を持つようにするものである。つまり、位相制御回路９では、バースト期間の終端タイミングで積分回路１１からの積分値Ｉ_Rを取り込むと、これを計算処理回路９ｂで計算して積分値ＩＲが零となるようにするための所定のプリセット値を算出し、これをカウンタ９ａにプリセットする。
【００４２】
ところで、第１の色副搬送波が上記の正しい位相から１８０゜位相がずれた状態でも、積分回路１１で得られるバースト期間での積分値Ｉ_Rは零となる。しかし、この場合には、乗算器４では、正しい色差信号Ｒ−Ｙが復調されないし、また、第２の色副搬送波も上記の正しい位相から１８０゜位相がずれたものとなるので、乗算器５から正しい色差信号Ｂ−Ｙが得られない。この実施形態では、これを上記の積分値Ｉ_B から検出することができる。
【００４３】
即ち、上記の数７から明らかなように、第２の色副搬送波が正しい位相を持つ場合には、カラーバースト信号の１サイクルの積分値は−πと負値であり、従って、バースト期間での積分値Ｉ_Bも負値となる。しかし、この第２の色副搬送波が正しい位相に対して１８０゜位相が異なると、上記数７において、cos(ω)が−cos(ω）となるので、バースト期間での積分値Ｉ_Bが正値となる。従って、位相制御回路９は、この積分値Ｉ_Bが負値であるか、正値であるかにより、色副搬送波生成回路６で生成される第１，第２の色副搬送波が正しい位相状態にあるのか、これよりも１８０゜ずれた状態にあるかを検出することができ、この積分値Ｉ_Bが正値である場合には、第１，第２の色副搬送波の位相を１８０゜異ならせるための制御情報も含んだ制御パラメータＰ_B，Ｐ_P（カウンタ９ａのプリセット値）を色副搬送波生成回路６に供給する。
【００４４】
なお、積分値Ｉ_Bが正値の場合、乗算器４，５からの色差信号Ｒ−Ｙ，Ｂ−Ｙなどの復調信号を正負極性反転するようにしてもよい（この場合、勿論、この復調された色差信号Ｒ−Ｙ，Ｂ−Ｙはディジタル信号であるから、その正負の極性を表わす符号を“１”，“０”反転することになる）。
【００４５】
以上のようにして、色副搬送波生成回路６からは、変調色信号Ｃ中のカラーバースト信号に位相同期した正しい位相の第１，第２の色副搬送波が生成されることになる。
【００４６】
ところで、このようにディジタル処理によって色復調を行なう場合、図７で説明したように、次に、乗算器４の復調信号のバースト期間での積分値Ｉ_Rの絶対値が零近傍であると、ライン毎に変調色信号Ｃの色副搬送波に対する第１，第２の色副搬送波の位相が進んだり、遅れたりし、変調色信号Ｃの色副搬送波に対する第１，第２の色副搬送波の位相のばらつきが生ずる。この実施形態では、このばらつきを以下のようにして抑える。
【００４７】
いま、連続する２つのライン１，２の近傍部分を示す図２において、ライン１の映像期間Ｔ_P1では、位相制御回路９からセレクタ１０を介して色副搬送波生成回路６に制御パラメータ（書込みアドレス）Ｐ_P1が供給され、この制御パラメータＰ_P1に応じた位相の第１，第２の色副搬送波が色副搬送波生成回路６で生成されているものとする。このとき、位相制御回路９には、ライン１を含めた過去のラインのいずれかのバースト期間Ｔ_Bで得られた零近傍の値Ａの積分値Ｉ_Rが所望の積分値Ｉ_R として保持されている。
【００４８】
このようにして、ライン１の映像期間Ｔ_P1では、制御パラメータＰ_P1に応じた位相の第１，第２の色副搬送波で変調色信号Ｃの復調が行なわれているが、これと同時に、このライン１のバースト期間Ｔ_B1で得られた零近傍の値Ａ’の積分値Ｉ_Rを用いてこれを零とすることができる制御パラメータＰ（即ち、カウンタ９ａのプリセット値）を計算処理回路９ｂで計算している。
【００４９】
その後、次のライン２のバースト期間Ｔ_B2になると、位相制御回路９はこの算出した制御パラメータＰによってカウンタ９ａを制御し（即ち、算出したプリセット値をカウンタ９ａにプリセットし）、これを制御パラメータＰ_B2として出力する。セレクタ１０はバースト期間Ｔ_B2の間これを選択して色副搬送波生成回路６に送る。従って、色副搬送波生成回路６からは、この制御パラメータＰ_B2に応じた位相の第１，第２の色副搬送波が生成され、これにより、乗算器４，５でカラーバースト信号が復調される。この復調期間の信号が積分回路１１で積分され、零近傍の値Ｂの積分値Ｉ_R として位相制御回路９に取り込まれる。
【００５０】
そこで、位相制御回路９では、計算処理回路９ｂが既に記憶されている上記の値Ａの絶対値｜Ａ｜と新たな積分値Ｉ_Rの値Ｂの絶対値｜Ｂ｜とを比較し、これら｜Ａ｜，｜Ｂ｜の関係が、
｜Ａ｜≦｜Ｂ｜
とすると、既に記憶している値Ａの積分値Ｉ_Rをそのままライン２でも保持するようにするとともに、ラインの映像期間Ｔ_P2でも、ライン１で用いた制御パラメータＰ_P1を再度色副搬送波生成回路６に送り、これに応じた位相の第１，第２の色副搬送波を生成させる。これとともに、このライン２の映像期間Ｔ_P2では、計算処理回路９ｂにより、バースト期間Ｔ_B2で得られた値Ｂの積分値Ｉ_Rから積分値Ｉ_Rを零とする制御パラメータＰを新たに算出する。この新たな制御パラメータＰは、ライン２の場合と同様に、次のライン３（図示せず）のバートス信号期間で用いる。
【００５１】
また、｜Ａ｜＞｜Ｂ｜の場合には、ライン２のバースト期間Ｔ_B2で用いた制御パラメータＰ_B2をこのライン２の映像期間での制御パラメータＰ_Pとして使用し（このとき、位相制御回路９から出力される制御パラメータＰ_Pは制御パラメータＰ_Bと同じものとなる）、これによって位相制御された第１，第２の色副搬送波が色副搬送波生成回路６から出力されるようにする。また、これまで保持されていた値Ａの積分値Ｉ_Rが破棄されて代わりに新たな値Ｂの積分値Ｉ_Rが保持されるとともに、この値Ｂの積分値Ｉ_Rから積分値Ｉ_Rを零にするような制御パラメータを算出し、次のライン３のバースト期間Ｔ_B3（図示せず）での使用に備える。
【００５２】
このようにして、各ラインにおいて、そのバースト期間では、１つ前のラインで算出した制御パラメータが積分値Ｉ_Rをより小さくするものであるかどうかの検査を行ない、その検査結果に応じて、次の映像期間では、積分値Ｉ_Rを小さくする方の制御パラメータを使用するものである。
【００５３】
即ち、第１，第２の色副搬送波は、バースト期間と映像期間とで独立に位相制御されることにより、積分値Ｉ_Rを小さくするように第１，第２の色副搬送波が位相制御されることになり、例えば、図７において、積分値Ｉ_Rが零近傍となったとき、第１，第２の色副搬送波が変調色信号Ｃの色副搬送波ａに対して破線ｂで示す位相のときの積分値Ｉ_Rが一点鎖線ｃで示す位相のときの積分値よりも小さい場合には、これら第１，第２の色副搬送波は破線ｂで示す位相の状態のままに保持され、逆の場合には、破線ｂで示す位相の状態から一点鎖線ｃで示す位相の状態に移ると、それ以降はこの一点鎖線ｃで示す位相の状態に安定化する。従って、変調色信号Ｃの色副搬送波ａに対する第１，第２の色副搬送波のライン毎のふらつきがなく、安定した色再現が可能となる。
【００５４】
なお、図２で説明したように図１に示した実施形態が動作するが、電源投入時のような入力アナログビデオコンポジット信号の色副搬送波がＡ／Ｄ変換器１のサンプルクロックや色副搬送波生成回路６の読出アドレスクロックと位相が全くランダムであって、この色副搬送波が色副搬送波生成回路６で生成される第１，第２の色副搬送波と位相が大きくずれている場合には、各ラインで位相制御回路９で保持されている積分値よりも積分回路１１から取り込む積分値の方が常に小さいものであり、積分回路１１から取り込む積分値に対する制御パラメータが使用されることになる。そして、これにより、入力アナログビデオコンポジット信号の色副搬送波に第１，第２の色副搬送波の位相が近づいていくことになる。
【００５５】
また、以上の実施形態では、乗算器４の復調出力のバースト期間での積分値 Ｉ_Rを用いて入力アナログビデオコンポジット信号の色副搬送波に第１，第２の色副搬送波の位相が近づくようにしたが、図３に示すように、色差信号Ｂ−Ｙを復調する乗算器５の復調出力のバースト期間での積分値Ｉ_Bを用いるようにしてもよい。但し、この場合には、上記数７の関係から、この積分値Ｉ_Bが大きくなる方向に第１，第２の色副搬送波の位相制御を行なう。即ち、位相制御回路９に保持されている積分値Ｉ_Bよりも積分回路１１から取り込む積分値Ｉ_Bが大きいとき、この取り込んだ積分値Ｉ_R から、上記のようにして、これを最大とする制御パラメータを求めるとともに、この積分値Ｉ_Bを保持するものである。なお、この場合には、この積分値Ｉ_Bを用いて、上記のように、第１，第２の色副搬送波の位相が正規の位相から１８０゜ずれているか否かを判定できるので、この積分値Ｉ_B のみを使用するだけでよい。
【００５６】
図４は本発明によるビデオ復調回路の他の実施例を示すブロック図であって、１２は加算器であり、図１に対応する部分には同一符号を付けて重複する説明を省略する。
【００５７】
同図において、乗算器４，５からの復調信号は加算器１２で加算され、積分回路１１は、図１における積分回路１１と同様の動作を行なって、バースト期間の開始タイミングからこの加算器１２の加算出力を積分し始める。位相制御回路９は積分回路１１で得られるバースト期間の積分値Ｉを取り込み、この積分値Ｉに応じたバースト期間での制御パラメータＰ_Bと映像期間での制御パラメータＰ_P とをセレクタ１０に出力する。
【００５８】
なお、積分回路１１が加算器１２の加算出力を積分する代わりに、乗算器４，５からの復調信号を夫々積分し、これによって得られた夫々の積分値を加算するようにしてもよい。
【００５９】
次に、この実施形態の水平ブランキング期間のバックポーチ部に重畳されているカラーバースト信号と色副搬送波生成回路６で生成される色副搬送波とを同期させる動作について説明する。
【００６０】
いま、入力アナログビデオコンポジット信号がＰＡＬ方式のビデオコンポジット信号とし、そのカラーバースト信号を、
【００６１】
【数８】
−cos(ω)＋sin(ω)
このビデオコンポジット信号での色差信号Ｒ−Ｙの色副搬送波を、
【００６２】
【数９】
sin(ω)
このビデオコンポジット信号での色差信号Ｂ−Ｙの色副搬送波（色差信号Ｒ−Ｙの色副搬送波に対して位相が９０゜異なる）を、
【００６３】
【数１０】
cos(ω)
とし、色副搬送波生成回路６で生成される第１の色副搬送波の位相が数９で示す色差信号Ｒ−Ｙの色副搬送波の位相と正確に一致しているものとすると、バースト期間での乗算器４の復調出力は、数８と数９とにより、
【００６４】
【数１１】
（−cos(ω)＋sin(ω))×sin(ω)
となり、また、同じくバースト期間での乗算器５の復調出力は、数８と数１０とにより、
【００６５】
【数１２】
（−cos(ω)＋sin(ω))×cos(ω)
となる。従って、バースト期間での加算器１２の加算出力は、
【００６６】
【数１３】
｛（−cos(ω)＋sin(ω))×sin(ω)｝＋｛（-cos(ω)＋sin(ω))×cos(ω)｝ ＝−cos(２ω)
となり、これをカラーバースト信号の１サイクル分、即ち、０〜２πに渡って積分すると、
【００６７】
【数１４】

【００６８】
となる。従って、この実施形態も、図１に示した実施形態と同様であり、位相制御回路９が積分回路１１からの積分値Ｉを零とするようなバースト期間と映像期間との制御パラメータを生成し、バースト期間で次の映像期間での制御パラメータの選択を行ない、これによって色副搬送波生成回路６からの第１，第２の色副搬送波の位相を制御する。
【００６９】
さらに、ＰＡＬ方式の場合、色差信号Ｒ−Ｙの色副搬送波の位相がライン毎に１８０゜ずれるので、位相制御回路９は、この色差信号Ｒ−Ｙを復調する第１の色副搬送波もこれに合わせてライン毎に１８０゜位相がずれるようにする制御パラメータを色副搬送生成回路６に送る。あるいはまた、第１の色副搬送波の位相をライン毎に１８０゜ずつずらす代わりに、乗算器４の次段に反転回路を設け、位相制御回路９がこの反転回路を制御することにより、乗算器４で復調される色差信号Ｒ−Ｙをライン毎に正負極性反転するようにしてもよい（この場合、勿論、この復調された色差信号Ｒ−Ｙはディジタル信号であるから、その正負の極性を表わす符号を“１”，“０”反転することになる）。
【００７０】
また、変調色信号Ｃでの色差信号Ｒ−Ｙの色副搬送波がライン毎に、
sin(ω)，−sin(ω)，sin(ω)，……
と１８０゜ずつ位相が変化し、乗算器４で復調された色差信号Ｒ−Ｙの色副搬送波がライン毎に、
−sin(ω)，sin(ω)，−sin(ω)，……
と変調色信号Ｃでの色差信号Ｒ−Ｙの色副搬送波の場合とは位相が１８０゜逆転している場合について考える。
【００７１】
いま、カラーバースト信号を、
【００７２】
【数１５】
−cos(ω)＋sin(ω)
色副搬送波生成回路６で生成される色差信号Ｒ−Ｙを復調するための第１の色副搬送波を、
【００７３】
【数１６】
−sin(ω)
色副搬送波生成回路６で生成される色差信号Ｂ−Ｙを復調するための第２の色副搬送波を、
【００７４】
【数１７】
cos(ω)
とすると、乗算器４の復調出力は、数１５と数１６とから、
【００７５】
【数１８】
（−cos(ω)＋sin(ω))×（−sin(ω))
となり、乗算器５の復調出力は、数１５と数１７とから、
【００７６】
【数１９】
（−cos(ω)＋sin(ω))×（cos(ω))
となる。これら乗算器４，５の復調出力をカラーバースト信号の１サイクル分、即ち、０〜２πに渡って夫々積分すると、
【００７７】
【数２０】

【００７８】
【数２１】

【００７９】
となる。
【００８０】
このことから、色副搬送波生成回路６で生成される第１の色副搬送波が−sin(ω)であり、乗算器４の復調出力のバースト期間の積分値Ｉ_Rと乗算器４の復調出力のバースト期間の積分値Ｉ_Bとがともに負であるとき、変調色信号Ｃの色副搬送波と色副搬送波生成回路６で生成される色差信号Ｒ−Ｙの復調のための第１の色副搬送波とはライン毎に１８０度ずれていることがわかる。従って、このときには、位相制御回路９は、制御パラメータにより、色副搬送波生成回路６を制御して第１の色副搬送波の位相を１８０゜反転させるようにするか、乗算器４の復調出力の正負を表わす符号を反転させるようにする。
【００８１】
以上のように、乗算器４，５の復調信号を加算器１２で加算し、その加算信号のうちの８〜１２サイクルのカラーバースト信号を含むバースト期間の部分を積分回路１１で積分し、制御回路６がその積分値に応じた制御パラメータで色副搬送波生成回路６を制御するとともに、色差信号Ｒ−Ｙを復調する第１の色副搬送波の位相がライン毎に１８０゜ずれるように色副搬送波生成回路６を制御することにより、積分回路１１での上記積分値が零となり、色副搬送波生成回路６から正しい位相の色副搬送波が生成されることになる。
【００８２】
なお、以上の各実施形態では、位相制御回路９をハード構成としたが、これをマイコンで構成してソフトウエア処理により同様の動作を行なうようにすることができる。
【００８３】
図５は以上説明した実施形態をビデオカメラ装置に適用した例を示すブロック図であって、１３はレンズ、１４は撮像素子、１５はＣＤＳ回路、１６は切替スイッチ、１７はＡ／Ｄ変換器、１８はカメラＤＳＰ（カメラディジタル信号処理）回路、１９はＹ／Ｃプロセス回路、２０は色変調回路、２１は電子ズーム回路、２２はＤ／Ａ変換器、２３はマイコン、２４は入力端子、２５はＹ／Ｃ分離回路、２６は色復調回路、２７は切替スイッチである。
【００８４】
同図において、撮像素子１４の出力をＤ／Ａ変換器２２からビデオ出力して得る場合には、切替スイッチ１６，２７をａ側に閉じる。レンズ１３によって撮像素子１４の受光面に結像された被写体映像が光電変換され、この撮像素子１４からアナログの映像信号が出力される。この映像信号は、ＣＤＳ回路１５で雑音の除去処理がなされた後、切替スイッチ１６を介してＡ／Ｄ変換器１７に供給され、ディジタル映像信号に変換されてカメラＤＳＰ回路１８に供給される。
【００８５】
このカメラＤＳＰ回路１８では、入力されたディジタル映像信号がＹ／Ｃプロセス回路１９でディジタル処理されて輝度信号Ｙと２つの色差信号Ｒ−Ｙ，Ｂ−Ｙとが生成され、これら色信号Ｒ−Ｙ，Ｂ−Ｙは色変調回路２０で変調されて変調色信号が生成される。これら色信号Ｒ−Ｙ，Ｂ−ＹとＹ／Ｃプロセス回路１９で生成せされた輝度信号Ｙとは、切替スイッチ２７を介してＤ／Ａ変換器２２に供給され、アナログの、例えば、ＮＴＳＣ方式のカラー映像信号として出力される。
【００８６】
また、外部から入力端子２４を介して入力される、例えば、ＮＴＳＣ方式のアナログビデオコンポジット信号を使用する場合には、切替スイッチ１６，２７をｂ側に閉じる。この場合には、この入力カラー映像信号はこの切替スイッチ１６を介してＡ／Ｄ変換器１７に供給され、ディジタルカラー映像信号に変換されてカメラＤＳＰ回路１８に供給される。
【００８７】
このカメラＤＳＰ回路１８では、入力されたディジタルカラー映像信号がＹ／Ｃ分離回路２５に供給されて輝度信号Ｙと変調色信号Ｃとに分離される。この変調色信号は色復調回路２６に供給され、上記のように動作して色差信号Ｒ−Ｙ，Ｂ−Ｙが復調される。これら復調された色差信号Ｒ−Ｙ，Ｂ−Ｙは、Ｙ／Ｃ分離回路２５で分離された輝度信号Ｙとともに、切替スイッチ２７を介してＤ／Ａ変換器２２に供給され、夫々アナログ信号に変換されてビデオ出力として出力される。
【００８８】
なお、切替スイッチ２７から出力されるディジタルの輝度信号Ｙと色差信号Ｒ−Ｙ，Ｂ−Ｙは、また、電子ズーム回路２１でフォーマット変換処理することにより、パソコンなどのマルチメディアに供給することができる。
【００８９】
かかる装置に上記の実施形態を適用することができ、その場合には、夫々の実施形態でのＡ／Ｄ変換器１はＡ／Ｄ変換器１７として用いられ、以下、Ｙ／Ｃ分離回路２はＹ／Ｃ分離回路２５として、色復調回路３は色復調回路２６として夫々用いるものである。
【００９０】
【発明の効果】
以上説明したように、本発明によれば、ディジタル化されたビデオコンポジット信号の変調色信号から色差信号Ｒ−Ｙ，Ｂ−Ｙを復調しても、得られるこれらの色差信号Ｒ−Ｙ，Ｂ−Ｙのレベルがライン毎に変動するということがなくなり、安定した色再現が簡単で部品点数の少ない回路構成で得られることになる。
【図面の簡単な説明】
【図１】本発明によるビデオ復調回路の一実施形態を示すブロック図である。
【図２】図１における位相制御回路の動作を示す図である。
【図３】本発明によるビデオ復調回路の他の実施形態を示すブロック図である。
【図４】本発明によるビデオ復調回路のさらに他の実施形態を示すブロック図である。
【図５】本発明によるビデオ復調回路の一適用例を示すブロック図である。
【図６】従来のビデオ復調回路の一例を示すブロック図である。
【図７】ディジタル処理によって変調色信号を復調する場合に生ずる不具合を示す図である。
【符号の説明】
１ Ａ／Ｄ変換器
２ Ｙ／Ｃ分離回路
３ 色復調回路
４，５ 乗算器
６ 色副搬送波生成回路
９ 位相制御回路
１０ セレクタ
１１ 積分回路
１２ 加算器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an analog video composite signal color demodulation circuit, and more particularly to a video signal demodulation circuit that demodulates two color difference signals RY and BY from a video composite signal by digital signal processing.
[0002]
[Prior art]
Conventionally, as a video signal demodulating circuit for demodulating two color difference signals RY and BY from an analog video composite signal, “NHK TV Technical Textbook (above)” pp. 129 172-184, demodulation processing is performed using an analog circuit such as a color carrier wave generation circuit and a phase control circuit using a crystal resonator, and then the demodulated signal is converted into a digital signal by an A / D converter. What to convert is known.
[0003]
However, such a video signal demodulating circuit requires many circuit components, and there are problems such as two A / D converters required for digitizing the color difference signal. Japanese Patent Laid-Open No. 8-214327 proposes a video signal demodulating circuit that can simplify the circuit and reduce the number of circuit parts by digitally demodulating the video composite signal.
[0004]
Referring to FIG. 6, the analog video composite signal is directly converted into a digital signal by the A / D converter 1, and the modulated color signal C is separated from the digital signal by the Y / C separation circuit 2, so that the color demodulation circuit 3 To be supplied.
[0005]
The color demodulation circuit 3 is provided with a color subcarrier generation circuit 6 including a first ROM storing sine wave data, a second ROM storing cosine wave data, and a ROM counter for generating read addresses thereof. The sine wave data is read from the first ROM as the first color subcarrier and the cosine wave data is read from the second ROM as the second color subcarrier according to the read address from the ROM counter.
[0006]
In this way, the first color subcarrier generated by the color subcarrier generation circuit 6 and the modulated color signal C separated by the Y / C separation circuit 2 are multiplied by the multiplier 4, whereby the color difference signal R−. Y is demodulated, and the second color subcarrier generated in the same manner and this modulated color signal C are multiplied by the multiplier 5 to demodulate the color difference signal BY.
[0007]
Further, the demodulated signal of the demodulated color difference signal RY in the burst period is integrated by the integrating circuit 7, and the microcomputer 8 counts the count value of the ROM counter (that is, the color subcarrier generating circuit 6 based on the integration result). , The addresses of the first and second ROMs) are controlled. The phases of the first and second color subcarriers generated from the first and second ROMs change according to the count value of the ROM counter. The microcomputer 11 uses the above integration results as a basis. The count value of the ROM counter is controlled so that the integration result becomes zero, whereby the phase is correctly set from the color subcarrier generation circuit 6 with respect to the color subcarrier of the modulated color signal C. , The second color subcarrier is generated.
[0008]
Here, the first color subcarrier for demodulating the color difference signal RY has the correct phase when there is a 90 ° phase difference from the burst signal of the modulated color signal. Therefore, when the color burst signal of the modulated color signal C is demodulated with the first color subcarrier having the correct phase in this way, the demodulated output is zero. Therefore, as described above, by controlling the phase of the first and second color subcarriers so that the integral value of the demodulated signal in the burst period of the demodulated color difference signal RY becomes zero, these first and second color subcarriers are controlled. The first and second color subcarriers have the correct phase with respect to the color subcarrier of the modulated color signal C.
[0009]
Thus, in the prior art described in the above-mentioned Japanese Patent Laid-Open No. 8-214327, color subcarrier generation and phase control for color demodulation are performed by digital processing. The circuit configuration is simplified and the number of circuit components can be reduced.
[0010]
[Problems to be solved by the invention]
However, in the above prior art in which color demodulation is performed by digital processing, color demodulation is performed only by digital signal processing. Therefore, when the absolute value of the integral value in the burst period of the demodulated color difference signal RY becomes close to zero. In some cases, the phase of the color subcarrier generated by the color subcarrier generation circuit 6 for each line (horizontal scanning period) approaches or moves away from the phase of the subcarrier of the digital video composite signal. Hereinafter, such a phenomenon will be described with reference to FIG. FIG. 7 shows one cycle of the color subcarrier.
[0011]
In the figure, a solid line a is now a color subcarrier of the modulated color signal C separated from the digital video composite signal (hereinafter referred to as an input color subcarrier), and a black circle is a sample point of the input color subcarrier a. Then, when the absolute value of the integrated value in the burst period of the demodulated color difference signal RY is close to zero, the first and second color subcarrier generation circuits 6 of the color demodulation circuit 3 described above generate the first and second. The phase of the color subcarrier (hereinafter referred to as the generated color subcarrier) is advanced or delayed with respect to the input color subcarrier a for each line, as in the waveform indicated by the broken line b or the alternate long and short dash line c. Here, the white circles in the generated color subcarriers b and c represent the sample points.
[0012]
Such a phenomenon is caused by the following.
That is, the color subcarrier generation circuit 6 reads the sine wave data and the cosine wave data with the read address clock that is phase-synchronized with the sample clock of the A / D converter 1 at the same frequency. Two color subcarriers are generated. On the other hand, the phase of the color subcarrier in the input analog video composite signal is not necessarily synchronized with the clock and is a random phase with respect to the clock. Therefore, the color subcarrier in the modulated color signal separated by the Y / C separation circuit 2, that is, the first and second colors generated by the input color subcarrier a and the color subcarrier generation circuit 6 in FIG. The phase relationship with the subcarrier is random.
[0013]
In the prior art shown in FIG. 6, the microcomputer responds to the integration value as described above so that the integration value obtained by the integration circuit 5 for the burst period component of the demodulated color difference signal RY becomes zero. The first and second color subcarriers are phase-synchronized with the input color subcarrier by controlling the phases of the first and second color subcarriers. When the read timing of the sine wave and cosine wave data from the first and second ROMs of the circuit 6 is to be changed, the change is an integral multiple of the period of the read address clock, and the change is discontinuous. Become. Therefore, even if the phases of the first and second color subcarriers are changed, the phase change amount is an integral multiple of the period of the read address clock.
[0014]
Therefore, in FIG. 7, the integration value obtained by the integration circuit 5 of the burst period component of the color difference signal RY demodulated on a certain line is close to zero (but not zero), and the generated color at this time It is assumed that the subcarrier has a phase relationship indicated by a broken line b with respect to the input color subcarrier a. Therefore, in the next line, the above-mentioned value for the generated color subcarrier is set so that the integrated value becomes closer to zero, that is, the phase difference between the generated color subcarrier and the input color subcarrier a is reduced. Phase control is performed, thereby delaying the phase of the generated color subcarrier. As described above, the amount of change in the phase of the generated color subcarrier can only be an integral multiple of the period of the read address clock. Therefore, if the phase difference between the input color subcarrier a and the generated color subcarrier b is smaller than one period of the read address clock, the generated color subcarrier in the next line is as indicated by a one-dot chain line c. The phase is delayed with respect to the input color subcarrier a.
[0015]
In the next line, control is performed so that the integration value obtained by the integration circuit 5 of the burst period component of the demodulated color difference signal RY becomes zero. In this case, the input color subcarrier a Since the generated color subcarrier c is delayed in phase, control is performed in the direction in which the phase is advanced. As a result, the generated color subcarrier is indicated by a broken line b.
[0016]
In this way, in the above prior art, in order to make the phase of the generated color subcarrier closer to the phase of the input color subcarrier a, the generated color subcarrier is changed from the color subcarrier b to the color subcarrier for each line. and also from color subcarrier c to color subcarrier b. When the color difference signals RY and BY are demodulated from the modulated color signal C with the generated color subcarriers having phases different by 90 ° and 180 ° with respect to the generated color subcarriers b and c, these color difference signals are output for each line. The direct current levels of RY and BY will fluctuate and color reproduction will be impaired.
[0017]
Further, in the above prior art, when demodulating an NTSC video composite signal, even if the phase relationship between the color subcarrier and the color subcarrier generated inside the demodulation circuit is shifted by 180 ° from the normal phase relationship, The absolute value of the integral value in the burst period of the demodulated color difference signal RY becomes close to zero. In such a case, faithful color reproduction cannot be performed. However, in the above-described conventional technology, no consideration is given to this point.
[0018]
A first object of the present invention is to provide a video signal demodulating circuit that eliminates such a problem, reduces the fluctuation of the phase of the generated color subcarrier for each line, and enables good color reproduction. .
[0019]
The second object of the present invention is to provide a video signal demodulating circuit that prevents the generated color subcarrier from being stabilized to a phase that is 180 ° different from the normal phase, and enables good color reproduction. There is.
[0020]
[Means for Solving the Problems]
In order to achieve the first object, according to the present invention, an input analog video composite signal is directly A / D converted into a digital signal, and a modulated color signal separated from the digital signal is demodulated to obtain a color difference signal. In this case, depending on the integration value of the demodulated color difference signal in the burst period, the phase of the color subcarrier for demodulation of the modulated color signal is independently determined in the burst period of the modulated color signal and the video signal period. It is something to control.
[0021]
In the burst period of each line, it is determined whether the phase of the color subcarrier in the next video period is equal to the phase set in the previous line or the phase corresponding to the integration value. It is determined by comparing the integral value obtained in step 1 with the integral value obtained in any of the previous lines.
[0022]
In order to achieve the second object, the present invention provides a digital signal obtained by subjecting an input analog video composite signal to A / D conversion as it is, and demodulating a modulated color signal separated from the digital signal. Is obtained, the positive / negative of the integrated value in the burst period of the demodulated color difference signal BY is determined, and the sign indicating the positive / negative of the demodulated color difference signal represents the correct content according to the determination result. It is something to control.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
1 is a block diagram showing an embodiment of a video demodulating circuit according to the present invention, wherein 9 is a phase control circuit, 9a is a counter, 9b is a calculation processing circuit, 10 is a selector, and 11 is an integrating circuit. The parts corresponding to are assigned the same reference numerals.
[0024]
In the figure, for example, an NTSC input analog composite signal is converted into a digital signal as it is by an A / D converter 1 and then supplied to a Y / C separation circuit 2, where a luminance signal Y, a modulated color signal C, The separated digital luminance signal Y is output as it is, and the separated digital modulation color signal C is supplied to the multipliers 4 and 5 of the color demodulation circuit 3. The multiplier 4 is also supplied with the first color subcarrier generated by the carrier color signal generation circuit 6, and the first color subcarrier and the digitally modulated color signal C are multiplied to produce a digital signal. The color difference signal RY is demodulated. The other multiplier 5 is also supplied with a second color subcarrier that is 90 ° out of phase with the first color subcarrier generated by the carrier color signal generation circuit 6. By multiplying the modulated color signal C, the digital color difference signal BY is demodulated.
[0025]
In such a configuration, an integration circuit 11, a phase control circuit 9, and a selector 10 are further provided. The integration circuit 11 is supplied with a burst gate signal representing the burst period of the digital modulation color signal C, and integrates the demodulated signals of the multipliers 4 and 5 during the burst period represented by this burst gate signal. That is, since only the color burst signal exists in the burst period of the modulated color signal C, the multiplier 4 multiplies the color burst signal and the first color subcarrier and outputs the result as a demodulated signal in the burst period. The multiplier 5 multiplies the color burst signal by the second color subcarrier and outputs it as a demodulated signal in the burst period. In the integrating circuit 11, the burst period of the multipliers 4 and 5 is output. The demodulated signals at are integrated. The integration circuit 11 is reset at the start timing of the burst period represented by the burst gate signal.
[0026]
The integrated value I of these burst periods obtained by the integrating circuit 11 _R , I _B Is taken into the phase control circuit 9 together with the end timing of the burst period by the burst gate signal. _R , I _B Two control parameters according to the control parameter P, ie, the control parameter P for controlling the phase of the color subcarrier in the burst period _B And a control parameter P for controlling the phase of the color subcarrier in the video period _P Is output. The selector 10 is controlled by the burst gate signal, and the control parameter P output from the phase control circuit 9 during the burst period. _B In the video period, the control parameter P _P Are respectively supplied to the color subcarrier generation circuit 6.
[0027]
The color subcarrier generation circuit 6 generates a second color subcarrier having a phase different from that of the first color subcarrier by 90 ° according to the control parameter selected by the selector 10, and supplies the second color subcarrier to the multipliers 4 and 5, respectively. Supply. In this case, in the color subcarrier generation circuit 6, the first and second color subcarriers generated thereby are phase-controlled by the control parameter from the phase control circuit 9. As described above, the selector 10 Thus, the control parameter supplied from the phase control circuit 9 to the color subcarrier generation circuit 6 is the control parameter P in the burst period. _B However, during the video period, the control parameter P _P Therefore, the first and second color subcarriers are phase-controlled independently of each other with different control parameters in the burst period and the video period.
[0028]
The color subcarrier generating circuit 6 includes a memory storing digital data representing a sine wave (hereinafter referred to as sine wave data) and a memory storing digital data representing a cosine wave (hereinafter referred to as cosine wave data). In this case, the control parameter output from the phase control circuit 9 is a read address of these memories. Therefore, the phase control circuit 9 has a counter 9a for generating the read address and the integral value I. _R , I _B And a calculation processing circuit 9b for determining a preset value of the counter 9a. The clock counted by the counter 9a is synchronized in phase with the same frequency as the sample clock of the A / D converter 1. The counter 9a may be provided on the color subcarrier generation circuit 6 side.
[0029]
Next, an operation of synchronizing the color burst signal superimposed on the back porch portion in the horizontal blanking period and the color subcarrier generated by the color subcarrier generation circuit 6 will be described.
[0030]
Now, the input analog video composite signal is an NTSC color video signal, and the color burst signal is
[0031]
[Expression 1]
−cos (ω)
The color subcarrier of the color difference signal RY in the video composite signal is
[0032]
[Expression 2]
sin (ω)
The carrier of the color difference signal BY in the video composite signal (the phase is 90 ° different from that of the color subcarrier of the color difference signal RY).
[0033]
[Equation 3]
cos (ω)
Then, when the first color subcarrier whose phase exactly matches the color subcarrier shown in Equation 2 is generated from the color subcarrier generation circuit 6, the demodulated output of the multiplier 4 in the burst period is From Equation 1 and Equation 2,
[0034]
[Expression 4]
−cos (ω) × sin (ω)
It becomes. When the demodulated output represented by Equation 4 is integrated over one cycle of the color burst signal, that is, over 0 to 2π,
[0035]
[Equation 5]

[0036]
It becomes.
[0037]
In addition, when the second color subcarrier whose phase exactly matches the color subcarrier shown in the above equation 3 is generated from the color subcarrier generation circuit 6, the demodulated output of the multiplier 5 during the burst period is From Equation 1 and Equation 3,
[0038]
[Formula 6]
−cos (ω) × cos (ω)
It becomes. When the demodulated output represented by Equation 6 is integrated over one cycle of the color burst signal, that is, over 0 to 2π,
[0039]
[Expression 7]

[0040]
It becomes.
[0041]
As described above, when the first color subcarrier from the color subcarrier generation circuit 6 has the correct phase as described above, the integration circuit 11 starts from the burst period multiplier 4 including the color burst signal of 8 to 12 cycles. When the demodulated signal is integrated, the integrated value becomes zero, and the phase control circuit 9 integrates the integrated value I from the integrating circuit 11. _R Control parameter P according to _B , P _P Is supplied to the color subcarrier generation circuit 6 to obtain the integral value I. _R Is controlled so that the first and second color subcarriers have the correct phase. That is, in the phase control circuit 9, the integration value I from the integration circuit 11 at the end timing of the burst period. _R Is calculated by the calculation processing circuit 9b to calculate a predetermined preset value so that the integral value IR becomes zero, and this is preset in the counter 9a.
[0042]
Incidentally, even when the first color subcarrier is 180 degrees out of phase with the correct phase, the integrated value I in the burst period obtained by the integrating circuit 11 is obtained. _R Becomes zero. However, in this case, the multiplier 4 does not demodulate the correct color difference signal RY, and the second color subcarrier is also 180 degrees out of phase with the correct phase. 5 cannot obtain a correct color difference signal BY. In this embodiment, this is the integral value I described above. _B Can be detected from.
[0043]
That is, as apparent from the above equation 7, when the second color subcarrier has the correct phase, the integral value of one cycle of the color burst signal is -π and a negative value. Integral value I _B Is also negative. However, if the second color subcarrier is 180 ° out of phase with the correct phase, cos (ω) becomes −cos (ω) in the above equation 7, so that the integral value I in the burst period is _B Becomes a positive value. Therefore, the phase control circuit 9 provides the integral value I _B Whether the first and second color subcarriers generated by the color subcarrier generation circuit 6 are in the correct phase state or 180 ° shifted from this depending on whether the signal is a negative value or a positive value. It is possible to detect whether there is an integral value I _B Is a positive value, the control parameter P including control information for causing the phases of the first and second color subcarriers to differ by 180 ° _B , P _P (Preset value of counter 9a) is supplied to the color subcarrier generation circuit 6.
[0044]
The integral value I _B Is positive, the demodulated signals such as the color difference signals RY and BY from the multipliers 4 and 5 may be inverted (in this case, of course, the demodulated color difference signal R- Since Y and BY are digital signals, the signs representing the positive and negative polarities are inverted by “1” and “0”).
[0045]
As described above, the color subcarrier generation circuit 6 generates the first and second color subcarriers having the correct phase in phase with the color burst signal in the modulated color signal C.
[0046]
By the way, when color demodulation is performed by digital processing in this way, as described with reference to FIG. 7, next, the integration value I in the burst period of the demodulated signal of the multiplier 4 is obtained. _R If the absolute value of is near zero, the phase of the first and second color subcarriers with respect to the color subcarrier of the modulated color signal C is advanced or delayed for each line, and the color subcarrier of the modulated color signal C with respect to the color subcarrier. Variations in the phase of the first and second color subcarriers occur. In this embodiment, this variation is suppressed as follows.
[0047]
Now, in FIG. 2 showing the vicinity of two consecutive lines 1 and 2, the video period T of line 1 is shown. _P1 Then, the control parameter (write address) P is sent from the phase control circuit 9 to the color subcarrier generation circuit 6 via the selector 10. _P1 Is supplied, and this control parameter P _P1 It is assumed that the first and second color subcarriers having the phases according to the color subcarrier generation circuit 6 are generated. At this time, the phase control circuit 9 includes any burst period T of the past line including the line 1. _B The integral value I of the value A near zero obtained by _R Is the desired integral value I _R Is held as.
[0048]
In this way, the video period T of line 1 _P1 Then, the control parameter P _P1 The modulated color signal C is demodulated by the first and second color subcarriers having a phase corresponding to the same, and at the same time, the burst period T of the line 1 _B1 The integral value I of the value A ′ near zero obtained by _R The calculation processing circuit 9b calculates a control parameter P (that is, a preset value of the counter 9a) that can be set to zero using.
[0049]
After that, the burst period T of the next line 2 _B2 Then, the phase control circuit 9 controls the counter 9a with the calculated control parameter P (that is, presets the calculated preset value in the counter 9a), and this is controlled by the control parameter P. _B2 Output as. The selector 10 has a burst period T _B2 During this period, it is selected and sent to the color subcarrier generation circuit 6. Therefore, the color subcarrier generation circuit 6 sends this control parameter P _B2 The first and second color subcarriers having the phases corresponding to the first and second color subcarriers are generated, whereby the multipliers 4 and 5 demodulate the color burst signal. The signal during this demodulation period is integrated by the integrating circuit 11, and the integrated value I of the value B near zero is obtained. _R Is taken into the phase control circuit 9.
[0050]
Therefore, in the phase control circuit 9, the absolute value | A | of the value A and the new integrated value I already stored in the calculation processing circuit 9b are stored. _R The absolute value | B | of the value B is compared, and the relationship between these | A | and | B |
| A | ≦ | B |
Then, the integral value I of the value A that has already been stored _R Is held in line 2 as it is, and the video period T of the line is also maintained. _P2 But the control parameter P used in line 1 _P1 Is again sent to the color subcarrier generation circuit 6 to generate the first and second color subcarriers having the phases corresponding thereto. At the same time, the video period T of this line 2 _P2 In the calculation processing circuit 9b, the burst period T _B2 The integral value I of the value B obtained in _R To integral value I _R A new control parameter P is set to zero. The new control parameter P is used in the Barts signal period of the next line 3 (not shown) as in the case of the line 2.
[0051]
If | A |> | B |, the burst period T of line 2 _B2 Control parameter P used in _B2 Control parameter P in the video period of this line 2 _P (At this time, the control parameter P output from the phase control circuit 9 is used. _P Is the control parameter P _B Thus, the phase-controlled first and second color subcarriers are output from the color subcarrier generation circuit 6. Also, the integral value I of the value A that has been held so far _R Is discarded and the integrated value I of the new value B is used instead. _R Is held, and the integral value I of this value B _R To integral value I _R The control parameter is calculated so as to make zero, and the burst period T of the next line 3 is calculated. _B3 Prepare for use in (not shown).
[0052]
Thus, in each line, in the burst period, the control parameter calculated in the previous line becomes the integral value I. _R In the next video period in accordance with the inspection result. _R The control parameter of the smaller one is used.
[0053]
That is, the first and second color subcarriers are phase-controlled independently in the burst period and the video period, so that the integral value I _R , The first and second color subcarriers are phase-controlled so that, for example, in FIG. _R Is the vicinity of zero, the integrated value I when the first and second color subcarriers are in the phase indicated by the broken line b with respect to the color subcarrier a of the modulated color signal C _R Are smaller than the integral value at the phase indicated by the alternate long and short dash line c, the first and second color subcarriers are held in the phase indicated by the broken line b, and in the opposite case, the broken line is indicated by the broken line. When the phase state indicated by b shifts to the phase state indicated by the alternate long and short dash line c, the state thereafter is stabilized to the phase indicated by the alternate long and short dash line c. Therefore, there is no wobbling for each line of the first and second color subcarriers with respect to the color subcarrier a of the modulated color signal C, and stable color reproduction is possible.
[0054]
As described with reference to FIG. 2, the embodiment shown in FIG. 1 operates. However, the color subcarrier of the input analog video composite signal when the power is turned on is the sample clock or color subcarrier of the A / D converter 1. When the phase of the read address clock of the generation circuit 6 is completely random and this color subcarrier is greatly out of phase with the first and second color subcarriers generated by the color subcarrier generation circuit 6 The integral value fetched from the integration circuit 11 is always smaller than the integral value held by the phase control circuit 9 in each line, and the control parameter for the integral value fetched from the integration circuit 11 is used. . As a result, the phase of the first and second color subcarriers approaches the color subcarrier of the input analog video composite signal.
[0055]
In the above embodiment, the integral value I in the burst period of the demodulated output of the multiplier 4 _R Is used so that the phase of the first and second color subcarriers approaches the color subcarrier of the input analog video composite signal. However, as shown in FIG. Integrated value I in burst period of demodulated output _B May be used. However, in this case, the integrated value I _B The phase control of the first and second color subcarriers is performed in the direction in which the value becomes larger. That is, the integral value I held in the phase control circuit 9 _B Integration value I taken from the integration circuit 11 rather than _B Is greater than this integrated value I _R Thus, as described above, the control parameter that maximizes this is obtained, and this integral value I _B Is to hold. In this case, the integral value I _B As described above, it is possible to determine whether or not the phase of the first and second color subcarriers is shifted from the normal phase by 180 °. _B Just use only.
[0056]
FIG. 4 is a block diagram showing another embodiment of the video demodulation circuit according to the present invention. Reference numeral 12 denotes an adder, and the same reference numerals are given to the portions corresponding to those in FIG.
[0057]
In the figure, the demodulated signals from the multipliers 4 and 5 are added by an adder 12, and the integrating circuit 11 performs the same operation as the integrating circuit 11 in FIG. Start integrating the added output of. The phase control circuit 9 takes in the integrated value I of the burst period obtained by the integrating circuit 11, and controls the control parameter P in the burst period according to the integrated value I. _B And control parameter P in the video period _P Are output to the selector 10.
[0058]
Instead of integrating the addition output of the adder 12, the integration circuit 11 may integrate the demodulated signals from the multipliers 4 and 5 and add the integrated values obtained thereby.
[0059]
Next, an operation of synchronizing the color burst signal superimposed on the back porch part in the horizontal blanking period and the color subcarrier generated by the color subcarrier generation circuit 6 in this embodiment will be described.
[0060]
Now, the input analog video composite signal is a PAL video composite signal, and the color burst signal is
[0061]
[Equation 8]
−cos (ω) + sin (ω)
The color subcarrier of the color difference signal RY in this video composite signal is
[0062]
[Equation 9]
sin (ω)
The color subcarrier of the color difference signal BY in this video composite signal (the phase is 90 ° different from that of the color subcarrier of the color difference signal RY).
[0063]
[Expression 10]
cos (ω)
Assuming that the phase of the first color subcarrier generated by the color subcarrier generation circuit 6 exactly matches the phase of the color subcarrier of the chrominance signal RY shown in Equation 9, The demodulated output of the multiplier 4 is expressed by the following equations (8) and (9).
[0064]
[Expression 11]
(−cos (ω) + sin (ω)) × sin (ω)
Similarly, the demodulated output of the multiplier 5 in the burst period is given by the following equations (8) and (10):
[0065]
[Expression 12]
(−cos (ω) + sin (ω)) × cos (ω)
It becomes. Therefore, the addition output of the adder 12 in the burst period is
[0066]
[Formula 13]
{(−cos (ω) + sin (ω)) × sin (ω)} + {(− cos (ω) + sin (ω)) × cos (ω)} = − cos (2ω)
When this is integrated over one cycle of the color burst signal, that is, over 0 to 2π,
[0067]
[Expression 14]

[0068]
It becomes. Therefore, this embodiment is also the same as the embodiment shown in FIG. 1, and the phase control circuit 9 generates control parameters for the burst period and the video period so that the integration value I from the integration circuit 11 is zero. The control parameter is selected in the next video period in the burst period, and thereby the phases of the first and second color subcarriers from the color subcarrier generation circuit 6 are controlled.
[0069]
Further, in the case of the PAL system, the phase of the color subcarrier of the color difference signal RY is shifted by 180 ° for each line. Therefore, the phase control circuit 9 also detects the first color subcarrier for demodulating the color difference signal RY. In response to this, a control parameter for causing the phase to shift by 180 ° for each line is sent to the color sub-carrier generation circuit 6. Alternatively, instead of shifting the phase of the first color subcarrier by 180 ° for each line, an inversion circuit is provided at the next stage of the multiplier 4, and the phase control circuit 9 controls the inversion circuit so that the multiplier 4 may be inverted for each line (in this case, of course, since the demodulated color difference signal RY is a digital signal, its polarity is changed) The sign to represent is inverted by “1” and “0”).
[0070]
Further, the color subcarrier of the color difference signal RY in the modulated color signal C is
sin (ω), −sin (ω), sin (ω), ……
And the phase of the color subcarrier of the color difference signal RY demodulated by the multiplier 4 is changed for each line.
−sin (ω), sin (ω), −sin (ω), ……
Consider the case where the phase is 180 ° reversed from the case of the color subcarrier of the color difference signal RY in the modulated color signal C.
[0071]
Now, color burst signal
[0072]
[Expression 15]
−cos (ω) + sin (ω)
A first color subcarrier for demodulating the color difference signal RY generated by the color subcarrier generation circuit 6 is
[0073]
[Expression 16]
−sin (ω)
A second color subcarrier for demodulating the color difference signal BY generated by the color subcarrier generation circuit 6;
[0074]
[Expression 17]
cos (ω)
Then, the demodulated output of the multiplier 4 is expressed by the following equations 15 and 16.
[0075]
[Formula 18]
(−cos (ω) + sin (ω)) × (−sin (ω))
The demodulated output of the multiplier 5 is expressed by the following equations 15 and 17.
[0076]
[Equation 19]
(−cos (ω) + sin (ω)) × (cos (ω))
It becomes. When the demodulated outputs of the multipliers 4 and 5 are integrated over one cycle of the color burst signal, that is, over 0 to 2π,
[0077]
[Expression 20]

[0078]
[Expression 21]

[0079]
It becomes.
[0080]
Therefore, the first color subcarrier generated by the color subcarrier generation circuit 6 is −sin (ω), and the integrated value I of the burst period of the demodulated output of the multiplier 4 is _R And the integral I of the burst period of the demodulated output of the multiplier 4 _B Are both negative, the color subcarrier of the modulated color signal C and the first color subcarrier for demodulation of the color difference signal RY generated by the color subcarrier generation circuit 6 are 180 degrees for each line. You can see that it is shifted. Therefore, at this time, the phase control circuit 9 controls the color subcarrier generation circuit 6 to invert the phase of the first color subcarrier by 180 ° according to the control parameter or outputs the demodulated output of the multiplier 4. The sign representing positive / negative is reversed.
[0081]
As described above, the demodulated signals of the multipliers 4 and 5 are added by the adder 12, and the part of the burst period including the color burst signal of 8 to 12 cycles of the added signal is integrated by the integrating circuit 11 and controlled. The circuit 6 controls the color subcarrier generation circuit 6 with a control parameter corresponding to the integral value, and the color subcarrier so that the phase of the first color subcarrier for demodulating the color difference signal RY is shifted by 180 ° for each line. By controlling the carrier generation circuit 6, the integration value in the integration circuit 11 becomes zero, and the color subcarrier having the correct phase is generated from the color subcarrier generation circuit 6.
[0082]
In each of the above embodiments, the phase control circuit 9 has a hardware configuration. However, the phase control circuit 9 may be configured by a microcomputer so that the same operation can be performed by software processing.
[0083]
FIG. 5 is a block diagram showing an example in which the above-described embodiment is applied to a video camera device, in which 13 is a lens, 14 is an image sensor, 15 is a CDS circuit, 16 is a changeover switch, and 17 is an A / D converter. , 18 is a camera DSP (camera digital signal processing) circuit, 19 is a Y / C process circuit, 20 is a color modulation circuit, 21 is an electronic zoom circuit, 22 is a D / A converter, 23 is a microcomputer, 24 is an input terminal, Reference numeral 25 denotes a Y / C separation circuit, 26 denotes a color demodulation circuit, and 27 denotes a changeover switch.
[0084]
In the figure, when the output of the image sensor 14 is obtained by video output from the D / A converter 22, the selector switches 16 and 27 are closed to the a side. The subject image formed on the light receiving surface of the image sensor 14 is photoelectrically converted by the lens 13, and an analog video signal is output from the image sensor 14. This video signal is subjected to noise removal processing by the CDS circuit 15, then supplied to the A / D converter 17 via the changeover switch 16, converted into a digital video signal, and supplied to the camera DSP circuit 18.
[0085]
In the camera DSP circuit 18, the input digital video signal is digitally processed by the Y / C process circuit 19 to generate a luminance signal Y and two color difference signals RY and BY, and these color signals R- Y and BY are modulated by the color modulation circuit 20 to generate a modulated color signal. The color signals RY and BY and the luminance signal Y generated by the Y / C process circuit 19 are supplied to the D / A converter 22 via the changeover switch 27 and are analog, for example, NTSC. Is output as a color video signal.
[0086]
When using, for example, an NTSC analog video composite signal input from the outside via the input terminal 24, the changeover switches 16 and 27 are closed to the b side. In this case, the input color video signal is supplied to the A / D converter 17 via the changeover switch 16, converted into a digital color video signal, and supplied to the camera DSP circuit 18.
[0087]
In the camera DSP circuit 18, the input digital color video signal is supplied to the Y / C separation circuit 25 and separated into the luminance signal Y and the modulated color signal C. The modulated color signal is supplied to the color demodulation circuit 26, and operates as described above to demodulate the color difference signals RY and BY. The demodulated color difference signals RY and BY are supplied to the D / A converter 22 via the changeover switch 27 together with the luminance signal Y separated by the Y / C separation circuit 25, and are converted into analog signals. It is converted and output as video output.
[0088]
The digital luminance signal Y and the color difference signals RY and BY output from the changeover switch 27 are supplied to multimedia such as a personal computer by the format conversion processing by the electronic zoom circuit 21. it can.
[0089]
The above-described embodiment can be applied to such an apparatus. In that case, the A / D converter 1 in each embodiment is used as the A / D converter 17, and hereinafter, the Y / C separation circuit 2 is used. Are used as the Y / C separation circuit 25 and the color demodulation circuit 3 is used as the color demodulation circuit 26, respectively.
[0090]
【The invention's effect】
As described above, according to the present invention, even when the color difference signals RY and BY are demodulated from the modulated color signal of the digitized video composite signal, these color difference signals RY and B are obtained. The −Y level does not fluctuate from line to line, and stable color reproduction is easy and a circuit configuration with a small number of parts can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an embodiment of a video demodulation circuit according to the present invention.
FIG. 2 is a diagram illustrating an operation of the phase control circuit in FIG. 1;
FIG. 3 is a block diagram showing another embodiment of a video demodulation circuit according to the present invention.
FIG. 4 is a block diagram showing still another embodiment of a video demodulation circuit according to the present invention.
FIG. 5 is a block diagram showing an application example of a video demodulation circuit according to the present invention.
FIG. 6 is a block diagram illustrating an example of a conventional video demodulation circuit.
FIG. 7 is a diagram illustrating a problem that occurs when a modulated color signal is demodulated by digital processing.
[Explanation of symbols]
1 A / D converter
2 Y / C separation circuit
3-color demodulator
4,5 multiplier
6-color subcarrier generation circuit
9 Phase control circuit
10 Selector
11 Integration circuit
12 Adder

Claims (8)

An A / D converter that converts an analog video composite signal into a digital signal; a Y / C separation circuit that separates a digital luminance signal and a digital modulated color signal from the digital signal; a first color carrier; A color subcarrier generation circuit for generating a second color carrier whose phase is 90 ° different from that of the color carrier, and the modulated color signal separated by the Y / C separation circuit and the first color carrier are multiplied. Then, the first color multiplier for demodulating the digital color difference signal RY, the digital color signal obtained by multiplying the digital modulated color signal separated by the Y / C separation circuit and the second color carrier, A video signal demodulating circuit comprising a second multiplier for demodulating Y;
An integrating circuit for obtaining an integral value of the signal component in the burst period of each of the demodulated digital color difference signals RY and BY;
A first control parameter for controlling the phase of the first and second color subcarriers in the burst period and the video period of the first and second color subcarriers by taking the integration value of the integration circuit A phase control circuit for generating a second control parameter for phase control at
The phase control circuit includes:
The integrated value obtained from the integrating circuit is held in any one of the sequential lines, and the first and second color sub-pixels generated in any one of the sequential lines First means for holding a control parameter as a second control parameter for phase control in a video period of a carrier wave;
For each line, the integrated value for the digital color difference signal RY obtained from the integration circuit during the burst period is taken, made zero, and the digital color difference signal B obtained from the integration circuit during the burst period. A second means for setting a control parameter for setting the integral value for -Y to a negative value, and setting the control parameter as the first control parameter in the burst period of the next line;
For each line, the absolute value of the integrated value for the digital color difference signal RY obtained from the integrating circuit in the burst period is compared with the absolute value of the integrated value held by the first means. 3 means,
A fourth means for changing the integral value held by the first means to the integral value having a smaller absolute value compared by the third means;
As a result of the comparison by the third means, when the absolute value of the integral value held in the first means is less than or equal to the absolute value of the integral value taken in by the second means, the first means The second control parameter for the next video period is set as the second control parameter for the next video period, and the integral value captured by the second means is the integral value held in the first means. And a fifth means for using the control parameter set by the second means as the second control parameter for the next video period
Have
The control parameters of the first to the burst period, by supplying the second control parameter to the video period each said color subcarrier generating circuit, said first, second for the color subcarrier of the digital modulation signal A video signal demodulating circuit for controlling a phase of a color carrier wave. An A / D converter that converts an analog video composite signal into a digital signal; a Y / C separation circuit that separates a digital luminance signal and a digital modulated color signal from the digital signal; a first color carrier; A color subcarrier generation circuit for generating a second color carrier whose phase is 90 ° different from that of the color carrier, and the modulated color signal separated by the Y / C separation circuit and the first color carrier are multiplied. Then, the first color multiplier for demodulating the digital color difference signal RY, the digital color signal obtained by multiplying the digital modulated color signal separated by the Y / C separation circuit and the second color carrier, A video signal demodulating circuit comprising a second multiplier for demodulating Y;
An integrating circuit for obtaining an integrated value of the signal component in the burst period of the demodulated digital color difference signal BY;
Incorporating an integral value of the integrating circuit, the first, the first control parameter and the first for position phase control in the burst period of the second color subcarrier, a second color subcarrier of the video A phase control circuit for generating a second control parameter for phase control in a period ;
The phase control circuit includes:
The integrated value obtained from the integrating circuit is held in any one of the sequential lines, and the first and second color sub-pixels generated in any one of the sequential lines A sixth means for holding a control parameter as a second control parameter for phase control in a video period of a carrier wave;
For each line, the digital chrominance signal B-Y obtained from the integrating circuit during the burst period is taken in, maximized, and the digital chrominance signal B obtained from the integrating circuit during the burst period. A seventh means for setting a control parameter for setting the integral value for -Y to a negative value, and setting the control parameter as the first control parameter in the burst period of the next line;
For each line, the absolute value of the integrated value for the digital color difference signal BY obtained from the integrating circuit in a burst period is compared with the absolute value of the integrated value held by the first means. 8 means,
Ninth means for changing the integral value held in the first means to the integral value having a larger absolute value compared by the third means;
As a result of the comparison by the third means, when the absolute value of the integral value held in the first means is equal to or larger than the absolute value of the integral value taken in by the second means, the first means The second control parameter for the next video period is set as the second control parameter for the next video period, and the integral value captured by the second means is the integral value held in the first means. A tenth means for using the control parameter set by the second means as the second control parameter for the next video period when
Have
By supplying the first control parameter in the burst period and the second control parameter in the video period to the color subcarrier generation circuit, respectively, the first and second colors for the color subcarrier of the digital modulation signal are supplied. A video signal demodulating circuit for controlling a phase of a color carrier wave . In claim 1 or 2,
The phase control circuit determines whether the integrated value is positive or negative with respect to the digital color difference signal BY obtained from the integrating circuit during a burst period, and when the integrated value is a positive value, the first and second color carriers The video signal demodulating circuit is characterized in that the color carrier wave generating circuit is controlled so that the phase of the signal is inverted by 180 ° . In claim 1 or 2 ,
The phase control circuit determines whether the integrated value is positive or negative with respect to the digital color difference signal BY obtained from the integrating circuit during a burst period, and when the integrated value is a positive value, is output from the first multiplier. A video signal demodulating circuit which inverts the sign indicating the sign of the digital color difference signal RY and the digital color difference signal BY output from the second multiplier . An A / D converter that converts an analog video composite signal in which the phase of the color subcarrier of the color difference signal RY is inverted by 180 ° for each line into a digital signal, a digital luminance signal and a digital modulated color signal from the digital signal A Y / C separation circuit for separating, a color subcarrier generation circuit for generating a first color carrier and a second color carrier having a phase difference of 90 ° with respect to the first color carrier, and the Y / C separation A first multiplier for demodulating the digital color difference signal RY by multiplying the modulated color signal separated by the circuit and the first color carrier; and the digital modulation separated by the Y / C separation circuit In a video signal demodulating circuit comprising: a second multiplier for demodulating the digital color difference signal BY by multiplying the color signal and the second color carrier;
An integrating circuit for obtaining a sum of integral values of the signal components in the burst periods of the demodulated digital color difference signals RY and BY;
A first control parameter for controlling the phase of the first and second color subcarriers in the burst period and the video period of the first and second color subcarriers by taking the integration value of the integration circuit and a phase control circuit for generating a second control parameter for phase control in provided,
The phase control circuit includes:
Eleventh means for performing control to invert the phase of the first color carrier generated by the color carrier generation circuit by 180 ° for each line;
The integrated value obtained from the integrating circuit is held in any one of the sequential lines, and the first and second color sub-pixels generated in any one of the sequential lines A twelfth means for holding a control parameter as a second control parameter for phase control in a video period of a carrier wave;
For each line, the control value for taking the integration value obtained from the integration circuit during the burst period and setting it to zero is set, and the control parameter is set to the first period in the burst period of the next line. A thirteenth means for the control parameter;
For each line, a fourteenth means for comparing the absolute value of the integrated value obtained from the integrating circuit in a burst period with the absolute value of the integrated value held by the twelfth means;
Fifteenth means for changing the integral value held in the twelfth means to the integral value having a smaller absolute value compared by the fourteenth means;
As a result of the comparison by the fourteenth means, when the absolute value of the integral value held in the twelfth means is less than or equal to the absolute value of the integral value taken in by the thirteenth means, the twelfth means The control parameter held in the second video control period is set as the second control parameter in the next video period, and the absolute value of the integral value fetched by the thirteenth means is the integral value held in the twelfth means. A sixteenth means that uses the control parameter set by the thirteenth means as the second control parameter for the next video period when
Have
By supplying the first control parameter in the burst period and the second control parameter in the video period to the color subcarrier generation circuit, respectively, the first and second colors for the color subcarrier of the digital modulation signal are supplied. A video signal demodulating circuit for controlling a phase of a color carrier wave . In claim 5 ,
The phase control circuit includes:
Eleventh means for performing control to invert the phase of the first color carrier generated by the color carrier generation circuit by 180 ° for each line;
The integrated value obtained from the integration circuit is held in any one of the sequential lines, and the first and second color sub-pixels generated in any one of these sequential lines A twelfth means for holding a control parameter as a second control parameter for phase control in a video period of a carrier wave;
For each line, the integrated value obtained from the integrating circuit during the burst period is taken and a control parameter for setting it to zero is set, and the control parameter is set to the first line in the burst period of the next line. A thirteenth means for the control parameter;
For each line, a fourteenth means for comparing the absolute value of the integrated value obtained from the integrating circuit in a burst period with the absolute value of the integrated value held by the twelfth means;
Fifteenth means for changing the integral value held in the twelfth means to the integral value having a smaller absolute value compared by the fourteenth means;
As a result of comparison by the fourteenth means, when the absolute value of the integral value held in the twelfth means is less than or equal to the absolute value of the integral value taken in by the thirteenth means, the twelfth means The control parameter held in the second video image period is set as the second control parameter in the next video period, and the integral value fetched by the thirteenth means is the integral value held in the twelfth means. A sixteenth means that uses the control parameter set by the thirteenth means as the second control parameter in the next video period when
Video signal demodulating apparatus characterized by having a. In claim 6,
Means for determining whether the integral value obtained by the integration circuit of the signal component in the burst period for each of the demodulated digital color difference signals RY and BY is positive or negative;
When the integral value for the demodulated digital color difference signal RY and the integral value for the demodulated digital color difference signal BY are both negative values, the color subcarrier generation circuit generates the first subcarrier generation circuit. Means for inverting the phase of one color subcarrier by 180 ° or inverting the sign representing the sign of the digital color difference signal RY demodulated by the first multiplier;
Video signal demodulating apparatus characterized by a provided. In any one of Claims 1-7,
The color carrier generation circuit adds an offset to the phases of the first and second color carriers in a video signal period and changes the phases of the demodulated color difference signals RY and BY. Video signal demodulation circuit.

Images