Patent ID: 6240147
Filing Date: 2001-05-29
Classification: H04L

Abstract:
An auto frequency control apparatus comprising:an amplifier for amplifying a frequency-shift keying signal;a local oscillation portion for transmitting a signal for converting the frequency-shift keying signal into a low-frequency signal;a mixer for mixing an output signal from said amplifier and an output signal from said local oscillation portion with each other;a demodulating portion for extracting a low-frequency signal from the output signal, the frequency of which has been converted by said mixer, so as to detect and demodulate the modulated signal;phase synchronizing means which makes coincide a frequency obtained by dividing the output signal from said local oscillation portion and a frequency obtained by dividing a reference signal with each other by detecting the phase difference between the two signals and which transmits a control voltage corresponding a result of the detection to said local oscillation portion so as to synchronize the phases;a reference-signal generating portion for generating the reference signal which is supplied to said phase synchronizing means;frequency-difference detection means connected to said phase synchronizing means, said frequency-difference detection means communicating a voltage corresponding to a result of the detection of the frequency difference between a carrier-wave signal for the frequency-shift keying signal and the output signal from said local oscillation portion in accordance with a result of the detection performed by said demodulating portion; anddivision-data setting means for setting a division ratio for dividing the frequency of a signal which is supplied to said phase synchronizing meanswherein said frequency-difference detection means is structured to always generate an output voltage signal for maintaining a state in which a central frequency of the spectrum of a received signal and the frequency of the output signal from said local oscillation portion coincide with each other when a direct conversation receiving method is employed.