Automatic gain control circuit and control method

An automatic gain control circuit and control method. A variable gain amplifier amplifies a differential input signal. The amplified signal is passed to a filtering circuit for filtering. The amplitude of the filtered output signal is checked using a peak value inspection circuit. The result of inspection is used to set the gain of the variable gain amplifier and further adjust the amplitude of the output signal. The peak value inspection circuit comprises a non-inverted phase differential comparator, an inverted phase differential comparator, an OR gate and a charge/discharge circuit. The output signal is compared with a reference signal through two differential comparators. The result of comparison controls the charge/discharge circuit so that the gain of the variable gain amplifier is varied and the amplitude of the output signal is controlled.