Patent ID: 6058093
Filing Date: 2000-05-02
Classification: G11B

Abstract:
A pre-pit detecting apparatus for detecting a pre-pit on an information record medium comprising (i) a record track on which record information can be recorded and (ii) a guide track which is to guide a light beam onto the record track and on which the pre-pit to record control information is formed in advance of recording the record information, said apparatus comprising:a light receiving device having four divided light detection areas each for receiving a reflection light of the light beam emitted on the record track, said four divided light detection areas being divided such that the reflection light beam at the light receiving device is divided by a first division line which is optically in substantially parallel to the record track and a second division line which is optically in substantially orthogonal to the record track, said four divided light detection areas having a first division area optically positioned on a side, which is close to the guide track where the pre-pit is formed, of the first division line and on a side, which is opposite to an advancing direction of the light beam, of the second division line, a second division area positioned on a side, which is opposite to the guide track where the pre-pit is formed, of the first division line and on the side, which is opposite to the advancing direction of the light beam, of the second division line, a third division area positioned on the side, which is opposite to the guide track where the pre-pit is formed, of the first division line and on a side, which is in the advancing direction of the light beam, of the second division line, and a fourth division area positioned on the side, which is close to the guide track where the pre-pit is formed, of the first division line and on the side, which is in the advancing direction of the light beam, of the second division line, said light receiving device outputting first to fourth light detection signals corresponding to the first to the fourth division areas respectively;a first difference signal generation device for generating a first difference signal by subtracting the third light detection signal from the first light detection signal;a second difference signal generation device for generating a second difference signal by subtracting the second light detection signal from the fourth light detection signal;a correction device for delaying the second difference signal by a delay time, which is set in advance in correspondence with a time difference between a light receiving timing of the light receiving device on the side, which is in the advancing direction of the light beam, of the second division line and that on the side, which is opposite to the advancing direction of the light beam, of the second division line, to output the delayed second difference signal;a pre-pit detection signal output device for adding the first difference signal and the delayed second difference signal to output it as a pre-pit detection signal; anda pre-pit detector for detecting the pre-pit on the basis of the pre-pit detection signal by using a predetermined threshold.