| 摘要 |
PURPOSE:To attain stable synchronous separating action by providing a circuit detecting the presence of a signal in vertical synchronism separation and switching a clamp level of a synchronism separation circuit by the said circuit so as to change over the state into the soft clamp state when lots of ghost signals exist. CONSTITUTION:A video detecting signal at an input terminal D is applied to vertical synchronizing separation circuits 5, 6. The separation circuit 5 has softer clamp constant than that of the separation circuit 6. Thus, if an input signal superposed with a negative ghost signal is inputted, the circuit 6 does not separate a vertical synchronizing signal earlier. The output from the circuit 6 is connected to a vertical synchronism detecting circuit 7, where the presence of the vertical synchronizing signal is detected. The detected output of the detecting circuit 7 is connected to a clamp constant switching circuit 8, and if no vertical synchronizing signal is detected by the circuit 8, the clamp level is changed over so that the clamp circuit of the separation circuit 5 performs softer clamp operation. |
