Patent ID: 6741416
Filing Date: 2004-05-25
Classification: G11B

Abstract:
A tracking signal generating device, comprising:a light source for emitting light; an optical system with which an information recording medium with a track from which information can be readout optically is irradiated with the light emitted from the light source as at least three optical beams; photodetectors for receiving optical beams reflected from the information recording medium; position signal generating sections for outputting three position signals Sm, Ss1, and Ss2 corresponding to each of the three optical beams and in accordance with a positional relationship between each of the optical beams and the track from signals obtained corresponding to a quantity of the optical beams entering the photodetectors; intermediate signal generating sections for receiving the three position signals Sm, Ss1, and Ss2, calculating differences between Sm and Ss1 and between Sm and Ss2 with the position signal Sm being taken as a reference, executing calculation for correction, and generating two intermediate signals Sa and Sb; and a signal synthesizing circuit for synthesizing a zero-crossing tracking signal in an arbitrary phase with respect to the track from the intermediate signals Sa and Sb, wherein the intermediate signal generating sections execute the correction so that the intermediate signals Sa and Sb have same amplitude levels and are different in phase by &pgr;/2 rad in a track crossing direction, and output the intermediate signals Sa and Sb, wherein the signal synthesizing circuit multiplies the two intermediate signals Sa and Sb input thereinto by coefficients &agr; and &bgr; given by &agr;=CÂ·sin &phgr; and &bgr;=CÂ·cos &phgr;or&agr;=CÂ·cos &phgr; and &bgr;=CÂ·sin &phgr;, where C and &phgr; are constants, and adds the multiplied intermediate signals Sa and Sb.