PHASE LOCKING DEVICE

摘要

PURPOSE:To expand a pull-in range of PLL equivalently without changing the pull-in range actually in spite of the offset of the frequency of an incoming input signal. CONSTITUTION:A multiplier 5 for video detection synchronously detects an intermediate frequency signal from an input terminal (a) by a carrier signal component reproduced by a voltage controlling oscillator 3, to reproduce a video signal at an output terminal (b). A frequency detecting means 6 is connected to the input terminal (a). The frequency detecting means 6 is provided with a frequency discriminator and a discriminated frequency controlling means to vary the intermediate frequency of the discriminator by the output signal voltage of the discriminator. The output voltage (d) of the frequency detecting means 6 is used as a control signal to follow the free-running frequency of a voltage controlling oscillator 3 to the frequency of the input signal.