Browse Prior Art Database

Erase/Write Digital-to-Analog Converter Power Calibration for the Optical Drives

IP.com Disclosure Number: IPCOM000106399D
Original Publication Date: 1993-Nov-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Finkelstein, BI: AUTHOR [+3]

Abstract

In most optical drive the erase and write power needs to be calibrated for variables such as temperature, bias field and media. The suggested erase and write power by the media manufacture is only good at nominal operating condition. It is useful for comparison purposes against the calibrated power.

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Erase/Write Digital-to-Analog Converter Power Calibration for the Optical Drives

      In most optical drive the erase and write power needs to be
calibrated for variables such as temperature, bias field and media.
The suggested erase and write power by the media manufacture is only
good at nominal operating condition.  It is useful for comparison
purposes against the calibrated power.

      A Digital-to-Analog Converter (DAC) is used to adjust the
required laser power for erase and write operation in the drive
electronic.  For given DAC value the laser output power can vary
drastically.  These changes come from component, laser efficiency and
temperature variation within a drive.  Therefore this DAC has to be
calibrated to the laser output power before any write calibration for
given media.

      One known technique uses a comparator to compare laser output
power from the auxiliary photodetector against some known reference
voltage.  The proposed technique in this disclosure uses the actual
read back signal to calibrate the erase and write DAC.  It can be
implemented in the drive ucode with no additional hardware.

      The general DAC calibration algorithm is shown in the flow
chart in the Figure.  This technique is also applicable to the WORM
and magnetic field modulation drives.  It is assumed the read power
is set to a precise value during the head manufacturing and the
tracking power in between erase and write pulses is less than the
read power level.

      For an accurate sampling of the read back signal, it is best to
use an uniform pattern (such as 3T, 4T,..) or a random pattern
embossed on every sector on the track.  Also, an averaging over a
sector can eliminated amplitude variation due to defects.

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