| 摘要 |
PURPOSE:To prevent malfunction of an SECAM discriminating circuit and to attain stable discriminating performance, even at a weak electric field, by obtaining a burst gate pulse to select a burst signal from a horizontal synchronizing signal gating noise. CONSTITUTION:Only the horizontal synchronizing signal of an inputted composite synchronizing signal is gated at a gate circuit 9, delayed at a delay circuit 2 to be a burst gate pulse. The pulse is inputted to a burst gate circuit 3, where the pulse is gated for the burst period only of the inputted color signal from a terminal 4 and the burst signal is outputted. The frequency is band-converted into DC for a PAL system burst signal, into about 30kHz for an R-Y signal component and about 180kHz for a B-Y signal in the SECAM signal burst signal. In selecting the center frequency of the 1st frequency selecting circuit 12 to 180kHz, a large and a small signal at each 1H are obtained at the output. In detecting this output at a detection circuit 6, a signal including fH/2(about 7.8kHz) component is obtained. Thus, the center frequency of the 2nd frequency selecting circuit 7 is selected to fH/2 and amplified, this is rectified at a rectifier circuit 8 and makes discrimination as the SECAM signal. |
