| 摘要 |
PURPOSE:To decrease the malfunction of squelch control due to the conditions of signal input and to stably control the squelch by controlling the squelch at 3 signal levels of the horizontal synchronizing level, the carrier level and the noise level. CONSTITUTION:An input signal 1 such as TV signals, etc., is added through a branch device 2 to a squelch control circuit 3 and a picture carrier selection amplifying circuit 5, the output of the circuit 5 is detected with a detection circuit 6 and branched into 3. Part of the branched output is added and processed to a picture amplifying circuit 7, a synchronizing cycle selection circuit 8 and a direct current amplifying circuit 9, the synchronizing level is detected and is inputted to a condition deciding logical operation circuit 15. The peak-to-peak value level of carrier waves of the picture signal from the branched output is preserved at a peak-to-peak value preserving circuit 11, and the noise components excluding the synchronizing cycle are removed with a band filter 12. The peak-to-peak value level and noise components are inputted to the circuit 15, a control circuit 3 is controlled under 3 conditions of the synchronizing level, the carrier level and the noise level and the malfunction of the squelch control is decreased. |
