Patent ID: 6108387
Filing Date: 2000-08-22
Classification: H04L

Abstract:
In an AFC circuit for a frequency scanning receiver comprising a voltage controlled oscillator for generating a frequency scanning signal; a frequency converter for generating a frequency error signal including a frequency error signal obtained from a received signal and said frequency scanning signal; a frequency discriminator for detecting the frequency error signal; and a signal detector for judging presence or absence of a desired received signal in an output of a signal intensity indicator obtained from a detection output of said frequency discriminator or an intermediate frequency amplifier section, which is so constructed that a control voltage is given to said voltage controlled oscillator, depending on a judgment output of said signal detector to stop said frequency scanning;an operating circuit, which calculates a voltage for setting the frequency at convergence of said AFC circuit, based on said frequency error signal and said control voltage; andcontrol means constituting an AFC loop by applying an output of said operating circuit to said voltage controlled oscillator;the improvement wherein said operating circuit comprises a first weighting circuit; an adding circuit; a second weighting circuit; and a holding circuit, in which said first weighting circuit weights said frequency error signal at the stop of said frequency scanning with a first weight; said adding circuit adds said control voltage at the stop of said frequency scanning to an output signal of said first weighting circuit; said second weighting circuit weights an output signal of said adding circuit with a second weight; and said holding circuit outputs an output signal of said second weighting circuit after having held it in a predetermined period of time.