| 摘要 |
PURPOSE:To improve the responsiveness of an input PSK signal against the fluctuation in a carrier transmission frequency by detecting the amplitude of a difference frequency component and controlling a band of a filter by the output according to the amplitude of the difference frequency component. CONSTITUTION:An output of phase detectors 2, 3 becomes a PSK demodulating output and signals A, B of points (a) and (b) of a base band processing circuit 4 become A=sin4 (DELTAomegat+theta0) and B=cos4(DELTAomegat+theta0), where DELTAomega is a frequency of difference between an output of a VCO10 and an input PSK signal and theta0 is a phase error. The signal B is differentiated into C=-4DELTAomega.sin4(DELTAomegat+theta0). Further, an output of a multiplication circuit 6 becomes D=1/2[-4DELTAomega+4DELTAomega.cos 8(DELTAomegat+theta0)]. That is, the signal D includes a component of a multiple of DELTAomega. The signals A and D are added by an adder circuit 8 and become a control voltage of the VCO10 via a filter 9. Thus, the VCO10 is controlled so as to be made coincident with the phase and the frequency of the carrier of the input PSK signal, a carrier regenerating circuit with AFC is constituted thereby expanding the locking frequency range. |
