Servo control system for information storage device

An optical disc system including a focusing mechanism and a tracking mechanism, wherein the mechanisms are controlled by feedback loops having electronic circuits for generating a servo error signals. The error signals are communicated in the feedback loop for effecting corrections of the focusing mechanism and the tracking mechanism. The optical disc system is provided with digital lead/lag compensation circuit assembly including a servo loop having servo loop transfer function and an error signal. The circuit assembly includes a motor or actuator having a mechanical resonance frequency being less than a predetermined sampling frequency and a compensation circuit for stabilizing the servo loop. The error signal of the servo loop is sampled at the pre-determined sampling frequency. Normalization of the error signals to the information signal occurs during sampling. The compensation circuit has a compensation transfer function including a single lead and a complex lag for producing a notch filter with a notch. The compensation transfer function is formulated so that the notch occurs at approximately one half the predetermined sampling frequency thereby reducing amplitude of the mechanical resonance frequency in the servo loop transfer function. The optical disc system also includes a mechanical isolator for vibration isolation and accommodation of thermal expansion, an oscillator with a tank circuit having an increased resistance, an improved focus capture system, and means for identifying blank sectors in a storage medium.