High Frequency Wobbles: A Write Clock Generation Method for Rewritable DVD That Enables Near Drop-In Compatibility with DVD-ROMs Daniel Abramovitch, David Towner, Craig Perlov, Josh Hogan, Michael Fischer, Carol Wilson, Ilkan C ¸ okg¨ or and Carl Taussig Hewlett-Packard Laboratories, Storage Technologies Department, 1501 Page Mill Road, M/S 4U-12, Palo Alto, CA 94304 USA August 2, 1999 ABSTRACT This paper describes a write clock generation scheme for rewritable DVD which eliminates a major issue for drop-in compatibility with DVD-ROMs. The method used is to co-locate a high frequency clock reference next to the data using a wobble groove. This enables bit accurate edits on rewritable DVD media. Keywords: High Frequency Wobbles, DVD-ROM Compatibility, Optical Recording, Write Clock Generation To appear in the Proceedings of ISOM/ODS’99 1. MOTIVATION This paper presents an overview of a new method of write clock generation on rewritable DVD drives that eliminates many of the problems associated with reading rewritable disks in DVD-ROM drives. It is believed that such a format will provide tremendous benefits to the end user, making it possible to edit content on a rewritable DVD disk and then play that same disk in a conventional DVD-ROM player. From a large set of potential problems, it appears that the real issues can be reduced to two: • smaller changes in reflectivity on phase-change media and • a much tighter clocking requirement caused by the need to eliminate edit gaps. Of these, the first is an issue for roughly half of the commercial DVD players in the world today. This issue can be overcome in the remainder with a simple circuit change in the AGC of the reader. It is the latter issue which is a problem. As shown in the bottom drawing of Figure 1, DVD-ROM disks have no edit gaps or physical sector marks. This is in contrast to conventional rewritable formats (the top two drawings of Figure 1) which need these gaps to accommodate imprecision in the write clock which would otherwise cause data loss at the end of data fields. 1–5 In order to match the DVD-ROM format, 6 a rewritable format must move away from what is depicted in the top two drawings to the bottom drawing of Figure 1. 2. HIGH FREQUENCY WOBBLE CLOCK In order to eliminate edit gaps and other in line sector information in a rewritable format, a new clocking scheme was devised that uses high spatial frequency groove edge oscillations (wobbles) to generate clock signals. This has the advantage that it co-locates clock reference with data, yielding a high fidelity, high frequency clock reference, as shown schematically in the left half of Figure 2. Using this, one can lock a narrow band phase-locked loop (PLL), as shown in Figure 3, to the oscillation frequency to generate the write clock. Addressing information can be encoded into the wobble itself using a variety of methods to eliminate the need for physical sector marks. Having a continuous clock co-located with the data is more precise and robust than intermittent clocks. The PLL can average over many clock cycles to ignore defects more easily. Furthermore, spindle runout, disk eccentricity and thermal variations have far less effect on the write clock. This means that there is virtually no drift between clock samples, allowing for the elimination of edit gaps. By encoding address information in the wobble itself, the Send correspondence to Daniel Abramovitch, E-mail: danny@hpl.hp.com, Phone: (650) 857-3806, FAX: (650) 857-7704 1