Patent ID: 8112052

Claim:
An automatic gain control system, comprising: an automatic gain control path including a first variable gain amplifier and a second variable gain amplifier, the first variable gain amplifier having a predetermined maximum gain control voltage corresponding to a predetermined maximum gain of the first variable gain amplifier, the second variable gain amplifier having a predetermined minimum gain control voltage corresponding to a predetermined minimum gain of the second variable gain amplifier; and a control device for controlling gain of the first variable gain amplifier and gain of the second variable gain amplifier, the control device including: an error calculator for calculating output signal and target value of the automatic gain control path, so as to generate an error signal; a hysteresis comparator for comparing a first estimation signal and a take over point (TOP) value, so as to produce a control signal; a first automatic gain control loop connected to the hysteresis comparator and the first variable gain amplifier for generating a first gain control signal according to the control signal so as to control the gain of the first variable gain amplifier; and a second automatic gain control loop connected to the hysteresis comparator and the second variable gain amplifier for generating a second gain control signal according to the control signal, so as to control the gain of the second variable gain amplifier; wherein, when the first estimation signal leaves the hysteresis area of the hysteresis comparator, the first gain control signal and the second gain control signal are increasing or decreasing progressively.