| 摘要 |
Although a head end lowers a level of TV synchronous signal at any time, a synchronous signal reproduction device reproduces the TV synchronous signal, and thus prevents a wiretapping of non-subscriber. The synchronous signal reproduction device includes: a trap(1) for selecting a carrier wave of a constant frequency; a first amplifier(2) for amplifying the carrier wave; impedance converter(3) for matching a carrier wave impedance of a constant frequency with CATV connected to an output terminal; a second amplifier(5) for amplifying a carrier signal from the impendance converter(3); filter(6) for tuning a carrier wave from the second amplifier(5); detector for detecting a data of a distorted synchronous signal loaded on the carrier wave; rectangular pulse generator(8) for converting a sine wave to a square wave; a controller(9) for checking a synchronous signal from the rectangular pulse generator(8), and controlling a peripheral system; synchronous signal width regulator(10); a synchronous signal detector for detecting a vertical synchronous signal; a synchronous signal converter for converting an output synchronous signal from the synchronous signal detector to an original synchronous signal; a tuning circuit(4) for receiving an original synchronous signal from the synchronous signal detector and an output voltage from a bias voltage determining part; a synchronous signal detector for detecting a synchronous signal having a regulated width; a shift register(14) for changing the detected synchronous signal to a clock signal, receiving a data and a clock signal, and converting a serial input data to a parallel data; a bias voltage determining part for providing a constant voltage to the tuning circuit according to an output data from the shift register(14); and mode selector(16) for receiving a vertical synchronous signal, and selecting a multiple mode.
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