Patent ID: 8482239

Claim:
A loop gain control circuit for servo control in which a position of a member to be driven is detected and the member to be driven is driven by an actuator such that the member to be driven is positioned at a target position, the loop gain adjusting circuit comprising: a sine wave adding unit that adds a sine wave to a compensation signal, wherein the compensation signal compensates the position of the member to be driven and is generated based on a position detection signal of the member to be driven, and wherein the sine wave adding unit obtains a signal which drives the actuator with the sine wave; an absolute value integrating circuit that integrates an absolute value of each signal before and after the sine wave adding unit adds the sine wave; and a gain adjusting circuit that compares two integrated values obtained by the absolute value integrating circuit, and adjusts a gain of an amplifier, wherein the amplifier amplifies the compensation signal such that the two integrated values are equal to each other.