Recording medium having a pilot signal with an aligned phase angle in adjacent tracks

Claim 1

In a recording medium having information recorded thereon in a plurality of substantially circular and concentrically-arranged information tracks, said recording medium being a light-reflective disc and each information track including a sequence of spaced regions of non-reflectivity representative of the recorded information, said recording medium being suitable for use with playback apparatus that recovers the recorded information by focusing a beam of light onto a selected track as the medium is moved in a prescribed fashion, to produce a reflected beam having an intensity modulated by the recorded pattern of regions of non-reflectivity, for detection by an information recovery device, an improvement wherein the recorded information comprises a modulated carrier signal and a pilot signal, said pilot signal having a prescribed, constant frequency substantially lower than a substantial portion of the frequency components of the modulated carrier signal, wherein the recorded pilot signal includes a prescribed, integral number of cycles on each track and the phase angle of the pilot signal is aligned with itself on adjacent tracks, and wherein the duty cycle of the recorded pattern of regions of non-reflectivity varies in accordance with the phase of the pilot signal, whereby the playback apparatus can function to controllably adjust the speed of the recording medium relative to the focused beam of light such that the phase angle of the recovered pilot signal component is substantially synchronized with the phase angle of a locally-generated reference signal, even when the beam of light is improperly focused on the recording medium such that the reflected beam is modulated by information recorded on more than a single information track, simultaneously, and even when the beam of light is traversing the recording medium from one track to another.