In a closed-loop control system and a servo device of an optical disk unit, a loop gain can be suitably corrected by a simplified structure. A signal is added to a closed loop and a value having a correlation with a gain of the closed loop is measured in accordance with the added signal. The loop gain...http://www.google.com/patents/US5521892?utm_source=gb-gplus-sharePatent US5521892 - Closed-loop control system and servo device of optical disk unit
