Disc device having eccentricity measurement and clock correction

Abstract

A magnetic or optical disc device which can correctly follow the eccentricity of an eccentrically chucked disk and Which can immediately follow the eccentricity of the new disk face when there is a changeover of the disc being accessed operates with a disc having data tracks provided with uniformly spaced clock marks for providing a timing standard and includes a reproduction circuit for reproducing data from the disc, a clock sampling circuit for extracting a first clock signal output by the reproduciton circuit, an eccentricity magnitude memory section for storing a signal corresponding to the eccentricity of the data tracks with respect to the axis of rotation of the disc; a clock correction section. The device further includes a voltage control oscillator operating according to the signal corresponding to the eccentricity for causing a second clock signal output by the voltage control oscillator to follow the first clock signal by changing the phase of the second clock signal or the frequency of the second clock signal and an eccentricity magnitude measuring section for measuring the signal corresponding to the eccentricity from the first clock signal and the output signal of the reproduciton circuit and supplying it to the eccentricity magnitude memory section. The eccentricity magnitude measuring section measures the signal corresponding to the eccentricity by calculating the number of tracks which the reproduction head crosses or by using the non-uniformity of spacing observed in a string of clock pulses reproduced from the uniformly spaced clock marks on the disc.