Teledyne LeCroy AORM - Advanced Optical Recording Measurements - Manual (Page 114)

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ISSUED: June 2013 923133 Rev A
APPENDIX A: NOTES ON ODATA MATH FUNCTION
The ORDATA math function can accept as input either unequalized or already equalized data,
and produce:
•
Equalized : If the input data is not already equalized, the instrument applies equalization
using the Filter Cutoff and Boost settings from the "Equalizer and PLL" dialog. The
result is low-pass filtered such that -3dB frequency, without boost, is the filter cutoff
frequency, and has high frequency boost applied such that the specified boost is reached
at about 61% of the filter cutoff frequency. The default values for cutoff frequency (8.2
MHz) and boost (3.2 dB) are the correct settings for 1x DVD and DVD-R.
•
Leveled : The data is fed to a 1 st order integrating low-pass filter whose bandwidth is set
by Slicer BW in the "Equalizer and PLL" dialog. The default slicer bandwidth (5.0 kHz) is
correct for 1x DVD and DVD-R. The output of this filter is subtracted from the waveform
to move the correct slice level to zero. Leveled output may be used for pit width
measurements, etc. The correct level for the parameter threshold is always zero volts
when it is used on leveled data.
•
Extract Clk : The sliced data is sent through a PLL emulation, and the output is the PLL's
VCO output. This uses the PLL BW setting in the "Equalizer and PLL" dialog. The default
PLL Bandwidth (9 kHz) is the correct setting for 1x DVD and DVD-R. The VCO's starting
frequency and phase are preset to attempt to start the PLL in a "locked" condition on
each sweep.
This appendix contains more information about each of these operations, including known limits
on their operations. Extracting the clock from the data has the most dependencies; if you plan to
use that function, please see the appropriate following section.
Equalized
Equalization can be applied if three conditions are met:
• We can make the low-pass filter.
• We can apply boost.
• The waveform is large enough to still have valid points after the filtering.
A warning message is displayed if any of these conditions is not met. If one of the following
warning messages appears, the waveform is NOT equalized:
• "LP fc low & sample rate too high, can't LP filter": The number of coefficients needed for
the finite impulse response (FIR) low-pass filter exceeded the maximum number
supported. The maximum is adequate for 1x DVD at 16 GS/s, which means the
maximum ratio of sample rate to cutoff frequency is 16e9/8.2e6 = 1951.22. This is far
above the maximum it is reasonable to use. See the note on computation time under
"Operational Notes."