Patent ID: 8644122
Filing Date: 2014-02-04
Classification: G11B

Abstract:
1. A header region evaluation circuit for evaluating a physical header region of an optical disc, the optical disc including both a groove and an inter-groove formed on the optical disc as information recording units that are formed of one recording spiral composed by alternately connecting a recording track on the groove and a recording track on the inter-groove, and the optical disc also being composed of a plurality of recording sectors including a physical header region and a recording region, the header region evaluation circuit comprising: a difference signal detection unit that detects a difference signal proportional to a difference in amounts of received light from the optical disc received by a light receiving element including light receiving units divided into two; a high pass filter that receives a passband control signal and the difference signal, switches at least a first cutoff frequency and a second cutoff frequency according to the passband control signal, removes a low frequency component from the difference signal, and generates a difference signal HPF output, the second cutoff frequency being set to a frequency lower than the first cutoff frequency; a waveform shaping unit that holds a pulse threshold and generates a shaping signal to convert the difference signal HPF output into a pulse using the pulse threshold; a physical header detection unit that measures duration of the pulse indicated by the shaping signal, detects the physical header region, generates a groove detection signal for evaluating whether the physical header region is either one of the groove and the inter-groove based on a detection result of the physical header region, and generates the passband control signal for controlling a cutoff frequency of the high pass filter to be reduced for the difference signal corresponding to at least a part of the physical header region.