Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Reexamination Certificate
2001-04-11
2003-12-16
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
C369S053100, C369S059110
Reexamination Certificate
active
06665243
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compact disc recording, and more specifically, to compact disc recording at a slow speed.
BACKGROUND
In compact disk technology, sub-1× recording, i.e. recording at a slower speed than reading speed, is used when real-time compression is used to reduce the data size for audio or video data. For example, a real time compression of audio data can result in a data rate that is as low as {fraction (1/10)}th of the uncompressed data. Real time video compression, such as MPEG-1 for VCD applications typically results in a 1× data rate after compression. Newer compression techniques, such as MPEG-4, can achieve even higher compression ratios. Thus, if real-time compression is used, the recording speed of the data will be below 1×.
Slower recording speeds have the advantage of reduced power consumption due to reduced rotational speed and laser power. However, for CD-R media the Orange book specifies a laser power for writing at 1× speeds (generally 1.2 to 1.4 meters/second tangential velocity of the recording head), and an equation to adjust the write power upwards for writing at higher speeds, at a multiple of the nominal velocity. However, no such equation is provided for writing speeds below 1×.
During a typical CD-R write operation, a mark is formed by switching the laser from read power to write power at the starting point of the mark, and switching back to read power at the ending point. Read power, typically an order of magnitude smaller than write power, is used to illuminate the disk between marks for tracking and focus servos. It is theoretically possible to write at sub-1× speeds by linearly reducing the write power to some low level.
The recording layer of CD-R media is optimized and tested to perform at a specified range of write speeds. Outside this range, the relationship of mark formation, write power, and writing speed becomes non-linear and unpredictable. Although for real-time data compression it is desirable to record data at speeds as slow as 0.05×(0.06 meters/second) no known CD or DVD recorder, media, or optical recording head is specified for writing at speeds less than 1×, nor is there guidance given in the Orange book.
Recording hardware, the recording head as well as the circuits that control write laser power, are designed to work for writing speeds over 1×. If sub-1× writing is attempted by simply reducing the write power, these elements may require substantial modifications. Writing at 1× power for sub-1× write speeds may damage the CD-R medium by overheating.
Therefore, a method of recording at sub-1× writing speeds without requiring substantive modifications to the recording head and laser power controls is needed.
SUMMARY OF THE INVENTION
A method and apparatus for sub-1× recording is described. The method of writing a mark on a compact disk (CD-R) medium spinning at a slow rate comprises varying the laser power between a write power and a read power while writing the mark, such that when read, the mark is read as a single mark.
REFERENCES:
patent: 5715228 (1998-02-01), Takiguchi
patent: 5751669 (1998-05-01), Shiratori
patent: 5848045 (1998-12-01), Kirino et al.
patent: 6285647 (2001-09-01), Van Woudenberg et al.
patent: 6396792 (2002-05-01), Ichihara
PCT Search Report dated Jul. 23, 2002, 3 pages.
Kelly John
Salmonsen Daniel R.
Blakely , Sokoloff, Taylor & Zafman LLP
Edun Muhammad
Zoran Corporation
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