Patent ID: 7035349

Claim:
A signal compensation circuit comprising: an amplifier receiving and amplifying an input signal to generate an amplified signal having a direct-current component and an amplitude, the amplifier having an adjustment terminal for adjusting the direct-current component of the amplified signal; an integrating circuit including a capacitor that can be charged and discharged at a rate determined by a time constant, the capacitor thus acquiring a potential, said potential being applied to the adjustment terminal of the amplifier; a low-speed compensation circuit for detecting changes in the direct-current component of the amplified signal and charging and discharging the capacitor in the integrating circuit in accordance with said changes, at the rate determined by the time constant of the integrating circuit; a high-speed compensation circuit for comparing the amplified signal with an allowable amplitude range, and charging and discharging the capacitor in the integrating circuit at a rate faster than the rate determined by the time constant of the integrating circuit, when the amplitude of the amplified signal goes outside the allowable amplitude range; and a threshold adjustment circuit for detecting changes in the amplitude of the amplified signal, and adjusting the allowable amplitude range in response to the detected changes in the amplitude.