| 摘要 |
The frequency shift keying (FSK) modulation circuit modulates frequency of reference signal using phase looked loop frequency synthesis method to generate stable FSK signal. The circuit comprises a reference signal generator (10), a phase detector (20) for detecting phase difference of a reference signal and output signal of a frequency divider (60), a low pass filter (30) for generating DC error signal by filtering error signal of the phase detector (20), a voltage controlled oscillator (40) for generating frequency controlled by DC error signal, a pre-scaler (50) for dividing frequency of FSK signal to decrease frequency, and a programmable frequency divider (60) for decreasing frequency of output signal of the prescalet (50) down to frequency of reference signal.
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