Patent ID: 7933369

Claim:
An apparatus for automatic gain control, comprising: an analog gain control unit for generating a gain control voltage for feedback-controlling an amplification value of an external amplification means in a high-precision range by an analog method; and a digital gain control unit for receiving the gain control voltage from the analog gain control unit and generating a digital code determining an amplification value of the external amplification means in a low-precision range by comparing the gain control voltage with an upper level reference voltage and a lower level reference voltage, wherein the analog gain control unit comprises: a mixer for squaring an output signal of the external amplification means; a low-pass filter for removing harmonics from the output signal of the mixer and converting the output signal into the gain control voltage and a reference level applier for applying a reference level to an output signal of the low-pass filter, and wherein the reference level applier comprises: a constant-current source for determining an output level for keeping an output level of the external amplification means uniform at an output level; and a voltage-control current source for generating current according to an output level of the mixer, wherein a difference in current between the constant-current source and the voltage-control current source is applied to the low-pass filter.