| 摘要 |
PURPOSE:To perform clamping stably even if a horizontal and a vertical synchronizing signals are not synchronized, by delaying a synchronizing signal, which is derived by a synchronizing separating circuit, in a monostable multivibrator by a prescribed quantity to cause it to correspond to a back porch of a horizontal synchronizing signal. CONSTITUTION:The TV signal input from terminal 1 is sent to clamp circuit 2 and synchronizing separating circuit 3. Synchronizing signal P1 derived by circuit 3 is delayed in monostable multivibrator 4 by a prescribed quantity and is caused to correspond to the back porch of the horizontal synchronizing signal. Output P2 of monostable multivibrator 4 and output P1 of circuit 3 are operated for AND by AND gate 5 to generate clamp pulse P2. Clamp pulse P3 from gate 5 is sent to circuit 2. If output P2 of monostable multivibrator 4 is in the position of vertical synchronizing signal S2, the TV signal is not raised because pulse P3 is not generated. As a result, stable clamping is performed even if horizontal and vertical synchronizing signals are not synchronized. |
