US Patent 7295820 Method and apparatus for DC offset control

An automatic gain control (AGC) circuit has an automatic gain controlled amplifier connected in series with a DC blocking capacitor. A reference DC voltage is selectively applied to an input of the automatic gain controlled amplifier and to an output of the DC blocking capacitor output so as to cause the DC blocking capacitor to store a charge proportional to a DC voltage offset introduced by the controllable gain amplifier. The selectively application of the reference DC voltage is momentarily applied for a duration of less than about 1 microsecond and preferably about 0.4 microseconds. The AGC circuit, including both the amplifier and capacitor, are fabricated as an integrated circuit device.