Focus servo circuit apparatus with automatic bias adjustments

摘要

In a recording and reproducing apparatus of CD or the like, it is adapted such that the time difference between an edge of a PLL clock synchronized with an EFM signal and a transition point of the EFM signal is measured in a time difference measuring circuit, a focus bias voltage to bring the time difference to a minimum is established in a bias voltage generator, the established focus bias voltage is added in an adder to a focus error signal generated in a focus error signal generator, and, thereby, the focus bias is automatically adjusted and focus servo is executed in accordance with the bias-adjusted focus error signal.