| 摘要 |
PURPOSE:To perform demodulation even when large fluctuation is generated in a carrier frequency by converting a frequency difference between the output signal of a frequency variable oscillator which oscillates synchronizing with a QPSK signal and a signal in which the QPSK signal is multiplied by four, and feeding it back to the frequency variable oscillator. CONSTITUTION:Phase information in the QPSK signal inputted from an input terminal 1 is eliminated by multiplying by four at a 4 multiplier 13, and is 4-frequency divided by a 4 frequency divider 14, and is inputted to a frequency comparator 16. The output signal of the frequency comparator 16, after being smoothed by a low-pass filter 17, is inputted to an adder 10. In such a way, it is possible to control the oscillation frequency of a VCO11 so as always to be approached the carrier frequency of the QPSK signal inputted to the input terminal 1, and to suppress the fluctuation of a free-run frequency due to the temperature change of the VCO11. |
