Patent ID: 6603726
Filing Date: 2003-08-05
Classification: G11B

Abstract:
A pre-pit detection unit comprising:a push-pull circuit for generating a radial push-pull signal including a pre-data signal according to each of lateral outputs of a light receiving element, a first pre-pit detection circuit for beam intensity in a mark period for detecting a pre-pit corresponding to the beam intensity in the mark period according to the radial push-pull signal obtained from said push-pull circuit, and a second pre-pit detection circuit for beam intensity in a space period for detecting a pre-pit corresponding to the beam intensity in the space period according to the radial push-pull signal obtained from said push-pull circuit, so that the OR of outputs of both pre-pit detection circuits is outputted as a pre-pit detection signal, wherein a first and a second AGC circuits for making the maximum amplitude of said radial push-pull signal obtainable from said push-pull circuit coincide with a reference value are provided in the preceding stages of pre-pit detecting comparators in said first and said second pre-pit detection circuits respectively.