| 摘要 |
PURPOSE:To exactly detect the time when there is no signal and the time when there is a signal, by connecting a retriggerable monostable multivibrator in 2 stages, to an output of an AC coupling type optical receiver. CONSTITUTION:When a pulse width modulating signal (a) is inputted to a monostable multivibrator 11 of the first stage togethr with carrier-on, a signal (b) synchronizing with a rise edge of the signal (a) is outputted, and is inputted to a monostable multivibrator 12 of the second stage. The vibrator 12 outputs a large pulse width signal than a pulse period of the signal (b), therefore, when a normal data is inputted, its output signal (c) becomes ''1''. When there is no signal, usually a high frequency noise (d) is generated, therefore, the vibrator 11 is retriggered one after another, and a state of ''1'' is held. When it is inputted to the vibrator 12, it is not triggered, the signal becomes a state of ''0'', and a carrier detectint signal becomes off. |
