Focusing control apparatus for an optical disk system employing a gain adjusted and phase compensated error signal

A focusing control apparatus comprising:

• an optical pick-up receiving a reflected light-beam and outputting a signal responsive to the reflected beam, the optical pick-up being adjustable for minimizing focusing error;
• a focusing error detector coupled to the optical pick-up, receiving the signal, determining a focusing error from the signal, and outputting a focusing error signal having a period and amplitude, the focusing error signal being responsive to the focusing error;
• a system state gain controller coupled to the focusing error detector, inputting the focusing error signal, and adjusting the amplitude of the focusing error signal responsive to the period of the focusing error signal and outputting an amplitude adjusted error signal;
• and
• an actuator coupled to the optical pick-up and to the system state gain controller, adjusting the optical pick-up to minimize the focusing error responsive the amplitude adjusted error signal.