| 摘要 |
PURPOSE:To extract character information surely and well from an analogue TV signal, by detecting and holding positive and negative peak values of the character information signal and by adding these peak values in a proper ratio and by using the addition output as a threshold voltage. CONSTITUTION:The output from a video detecting circuit 4 is supplied to positive and negative peak detecting circuits 9 and 10, and positive and negative peak values are detected and held in holding capacitors 11 and 12. These peak values are supplied in a ratio due to resistances 13 and 14 to a comparing circuit 15 and are compared with the video output of the circuit 4 to extract data. This circuit is provided with clamping transistors 18 and 19, and the divided voltage from a connection point PC between resistances 13 and 14 is applied to a gate circuit 20 which is opened in the time of a clock line RI. A gate pulse GR which becomes H in the time of the line RI is applied from a gate pulse forming circuit 23 to the circuit 20, and an intermediate voltage between positive and negative hold voltage is supplied to transistors 18 and 19 through a hold circuit 24 in the time of the line RI. |
