Automatic gain control circuit and automatic gain control method

An automatic gain control (AGC) circuit of a demodulating circuit, which has an automatic gain control amplifier for adjusting a gain of a modulated signal, comprising:

• difference detecting means for calculating a plurality of power values of pieces of symbol information of in-phase components and quadrature components of the modulated signal and detecting a power difference between each calculated power value and an ideal power value;
• control means for producing an AGC control signal to reduce an average value of the power differences detected by the difference detecting means to zero by controlling the automatic gain control amplifier according to the AGC control signal;
• first correcting means for minimizing a bit error rate of data, which is obtained from the modulated signal in the demodulating circuit, by correcting the AGC control signal produced by the control means;
• and
• second correcting means for correcting the ideal power value to reduce an average value of the power differences detected by the difference detecting means, in which the power differences are detected from the modulated signal adjusted by the automatic gain control amplifier according to the AGC control signal corrected by the first correcting means, to zero, wherein each power difference detected by the difference detecting means is multiplied by a prescribed gain by the second correcting means to produce a multiplied value, the multiplied value is transmitted through a loop filter of the second correcting means, the multiplied value transmitted through the loop filter is added to the ideal power value to produce a corrected ideal power value and to detect power differences produced from the corrected ideal power value.