Frequency estimating circuit and AFC circuit using the same

An AFC circuit comprising:

• a frequency detector circuit including a time-axis to frequency-axis converter circuit for converting an input data stream that is obtained by over-sampling a received signal at a symbol rate T times m on a time axis into a power spectrum on a frequency axis, and a MAX search circuit for searching, in an observation frequency range -f.sub.S /2.about.f.sub.S /2 determined by a sampling rate f.sub.S =m/T, for a frequency f.sub.1 corresponding to a maximum value of the power spectrum,
• a frequency computing circuit for estimating a plurality of frequency information f.sub.EST as a candidate for a frequency offset .DELTA.f of a carrier of the received signal through the computation noted below based on the frequency f.sub.1 corresponding to the maximum value of the power spectrum determined by said frequency detector circuit and for outputting frequency information,
• f.sub.EST =f.sub.1 +n.multidot.f.sub.S
• n:
• an integer that meets f.sub.L .ltoreq.(f.sub.1 +n.multidot.f.sub.S).ltoreq.f.sub.U
• f.sub.L :
• lower limit of the distribution range of .DELTA.f
• f.sub.U :
• upper limit of the distribution range of .DELTA.f,
• a frequency correction block for producing a plurality of demodulated data streams by removing the frequency offset .DELTA.f from the received signal based on the plurality of frequency information output from the frequency computing circuit, and
• a determining circuit for determining frequency synchronization using the plurality of demodulated data streams output from the frequency correction block.