AMPLITUDE MODULATED COARSE POSITION ERROR SIGNAL GENERATION IN AN OPTICAL DISK STORAGE SYSTEM EMPLOYING COARSE SERVO TRACKS

摘要

A linear detector (31) for use in a coarse positioning servo system of an optical disk storage system. The linear detector produces an error signal (67) having an amplitude linearly proportional to the distance that a center of mass of incident radiant energy (63) falls on a collection surface (62) of the detector as measured relative to a fixed reference point on said collection surface. Two reference signals (65, 66) are derived from circuitry associated with the collection surface. A first reference signal (65) has an amplitude proportional to the intensity of the focussed light energy and the location that said light energy falls on the collection surface relative to a first reference point. A second reference signal (66) has an amplitude proportional to the intensity of the focussed light energy and a location that said energy falls on the collection surface relative to a second reference point. The sum and difference of the amplitudes of the first and second reference signals are derived to produce sum and difference signals (Y, X), respectively. The difference signal is divided by the sum signal (X/Y) to produce the desired error signal, which error signal has an amplitude that is substantially independent of the intensity of the focussed light energy. Signal processing circuitry (84, 86, 88; and 85, 87, 89) may be used to demodulate the reference signals so that the desired error signal is derived only from that portion of the incident radiant energy reflected from a coarse servo track of the optical disk, and not from radiant energy reflected from other areas of the disk.