Servo circuit for an optical disk information recording and reproducing apparatus with improved stability for tracking and focusing control

A servo circuit of an optical disk information recording and reproducing apparatus comprising photodetecting means receiving a return light of a laser beam irradiated on said optical disk having a writable record area and an address area on which address signals for designating the record area are prerecorded presenting physical changes in the form, an optical system for focusing and tracking said laser beam under control of drive coil means, matrix circuit means for performing arithmetic operations on and processing of detected signals from the photodetecting means and outputting focusing error signals and tracking error signals therefrom, signal processing circuit means for phase compensating said focusing error signals and tracking error signals, and drive circuit means for amplifying output signals of said signal processing circuit means to an optimum level and for supplying said signals as drive signals for focusing and tracking to said drive coil means of the optical system,

• characterized in that the servo circuit further comprises:
• switch means for opening and closing the supply lines of said focusing error signals and tracking error signals supplied to said drive coil means, and
• address detecting circuit means for detecting an interval when the laser beam irradiates the address area of said optical disk on the basis of the detected signals by said photodetecting means,
• wherein said switch means disconnects said focusing error signals and tracking error signals from said drive coil means during the detected interval when the laser beam is irradiating the address area of the optical disk so that no error signal is applied to said drive coil means during said interval, said optical system being controlled by inertia through coasting during the interval when said laser beam is irradiating said address area.