Automatic frequency control apparatus and method therefor

An automatic frequency control apparatus comprising:

• local oscillation means for outputting a local oscillation signal having an oscillation frequency controlled by a frequency control voltage;
• quadrature detection means for quadrature-detecting a received signal using the local oscillation signal from said local oscillation means;
• frequency offset value estimation means for estimating a frequency offset value from quadrature detection signals received from said quadrature detection means;
• demodulation means for demodulating the quadrature detection signals from said quadrature detection means;
• synchronization determination means, coupled to said demodulation means, for determining reception synchronization according to demodulated signals received from said demodulation means to output a synchronization determination signal when reception synchronization with a single received frequency is established;
• frequency control means, coupled to said local oscillation means and said synchronization determination means, for generating said frequency control voltage and outputting said frequency control voltage to said local oscillation means;
• non-volatile memory means, coupled to said frequency control means, for storing a frequency control voltage obtained from said frequency control means when said reception synchronization is established;
• and
• power-on state detection means for detecting a power-on state to output a detection signal;
• said frequency control means being further coupled to said frequency offset value estimating means and said power-on state detection means, for repeatedly changing a frequency control voltage to be outputted to said local oscillation means according to the frequency offset value received from said frequency offset value estimation means until reception synchronization is established when no synchronization determination signal is output from said synchronization determination means,
• said memory means storing a frequency control voltage at which reception synchronization is established when the synchronization determination signal is output from said synchronization determination means to said frequency control means, and
• said frequency control means determining the oscillation frequency of said local oscillation means from a frequency control voltage read out from said memory means when the detection signal is output from said power-on state detection means.

A method of automatically controlling a frequency, comprising steps of:

• quadrature-detecting a received signal using a local oscillation signal from local oscillation means having an oscillation frequency controlled by a frequency control signal;
• estimating a frequency offset value of quadrature detection signals;
• demodulating the quadrature detection signals and obtaining demodulated signals;
• determining reception synchronization according to said demodulated signals;
• generating said frequency control signal in a frequency control means and outputting said frequency control signal to said local oscillation means;
• when no reception synchronization is established, repeatedly changing a frequency control voltage according to an estimated frequency offset value until reception synchronization is established;
• when reception synchronization is established, storing a frequency control voltage obtained when the reception synchronization is established;
• and
• when a power supply is turned on, controlling the oscillation frequency of said local oscillation means by the stored frequency control voltage, wherein the frequency control voltage obtained when the reception synchronization is established is stored in non-volatile storage means.