| 摘要 |
PURPOSE:To obtain an accurate character multiplex image by performing gain control in automatically detecting the shift of the superposition position and the number of times of superposition H of a character multiplex signal on a transmission side. CONSTITUTION:The detection output of a video detecting circuit 3 is applied to a character multiplex signal separating and shaping circuit 7 and a synchronizing signal and bit clock reproducing circuit 9. A video signal is passed through an amplifying circuit 13 to hold the level of the character multiplex signal constant by an automatic gain control signal 21 obtained by an automatic gain control circuit 26. The character multiplex signal held at the constant level is converted by a comparator 14 into a binary signal, and then sampled by a multiplex signal sampling circuit 15 by using a sampling signal generated by said reproducing circuit 9. Then, its output is passed through an error correcting circuit 8 to output a character signal. Automatic gain control circuit 26 is brought under gain control during the detection period of a clock-line signal, so the level of a multiplex position is held constant all the time, thus obtaining the accurate character signal. |
