| 摘要 |
PURPOSE:To make a circuit small-size and high-S/N by consituting a phase lock loop by a voltge control oscillator, a phase comparator and a loop filter and constituting a muting circuit by a level muting circuit and a band muting circuit. CONSTITUTION:A phase lock loop is constituted by voltage control oscillator 13 having a prescribed free-running frequency, phase comparator 14 which detects the phase difference between the output of oscillator 13 and the input signal, and loop filter 15 which is connected to the output end of comparator 14 and gives the output filtered as the oscillated frequency control signal for oscillator 13, and FM demodulation signals are outputted from the output end of filter 15. Meanwhile, muting circuit 20 is constituted by level muting circuit which is operated by detecting the magnitude of the input signal and a band muting circuit which is operated by detecting the deviation of the center frequency of the input signal. As a result, these circuits can be easily incorporated in one IC and made small-size, and a high S/N can be realized by phase comparison in IF. |
