Picture signal receiving circuit

Abstract

Abstract PURPOSE:To prevent the deadlock of an AGC loop when an excessive optical signal is inputted at the time of the input of a silence signal by providing a pilot extracting preamplifier on the output of a photodetector and executing an AGC operation to the photodetector and an automatic gain control amplifier (AGC) by the extracted pilot signal. CONSTITUTION:The pilot signal extracting preamplifier 3 for extracting and amplifying the pilot signal superimposed on the output of the photodetector 1 is provided to execute the AGC by the extracted pilot signal. A pilot signal level is lower by 10dB-20dB than the picture signal level of a main signal. Further, the pilot signal has a frequency completely separate from the picture signal. Thereby, even at the time of inputting the excessive optical signal from the state of the absence of an optical input, the signal is not dissipated even though the output of the pilot signal extracting preamplifier 3 is distorted but the pilot signal can be constantly detected and the AGC operation is maintained in this case to prevent the deadlock of the AGC loop.

Inventors

• 👤 Masaaki Takahashi
• 👤 正昭 高橋
• 👤 Haruo Yamashita
• 👤 治雄 山下
• 👤 Shinji Ota
• 👤 太田　眞治
• 👤 Tetsuo Soejima
• 👤 哲男 副島

Bibliographic Details