High density storage of information on a compact disc

Abstract

An optical storage system achieves high density, sufficiently high to permit both video and audio to be stored on a compact disc, or to store other data at very high density. Pits are encoded on the disc storage medium with respect to timed electronic reference signals (not simultaneously optically encoded on the disc) which divide each revolution of the disc into a multiplicity of equal spaces or references. The pits have leading edges on the leading side of a reference signal and trailing edges on a trailing side of the reference signal, so that each pit staddles a reference signal. The length of the pit leading up to the reference signal represents one sample of information, while the length of the pit from the reference signal to the pit's trailing edge represents another sample of information. In this manner high density is achieved at high accuracy and low noise, since one end of each bit of information is precisely located and readable without the lesser precision involved in determining the location of the leading and trailing edges of the pit in reading the information. On the disc the reference signal frequency is generated during the vertical retrace interval(s), encoded by equally spaced pits, for correlation with the prevailing speed of revolution of the disc. At each horizontal picture line (e.g., 525 per revolution) there is at least one reference pit. When this is detected the amount of phase shift which may exist at that line is measured and corrected for. Two samples of the video waveform are reproduced and measured for each pit. Small compact video discs can be produced with inner diameters of 2" to 4", or video bandwidths of up to 10 MHz can be produced for high resolution pictures.

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