Teledyne LeCroy AORM - Advanced Optical Recording Measurements - Manual (Page 82)

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ISSUED: June 2013 923133 Rev A
Example
The example shows that, measured at the selected voltage threshold, the CD data signal
contains sequentially a 5T pit, 3T space, 3T pit, and 4T space. If the measurement is configured
to select only 3T pits or spaces then the value displayed will be:
pwid = (694 ns + 696 ns) / 2 = 695 ns
Example 2: Histogramming
Consider the problem of determining the error margin in an optical recording system. Because the
data is encoded in the widths of the pits/spaces, it would be ideal for the widths to be exact
integer multiples of the period of the clock used to sample the data signal. In practice this is not
the case, but in order to ensure error-free data recovery, it is important for the widths to be
grouped and separated.
Histogramming can be used to analyze the grouping of pit widths and to determine whether the
separation is acceptable.
The scope is set up to acquire the optical data waveform by assigning Channel 1 to the data
signal at a time/div of 0.2 ms, so that many pits/spaces can be gathered quickly. The signal is
AC-coupled, so the threshold is set to 0 mV.
The pwid custom parameter is assigned to P1 and configured in the following manner:
hysteresis = 0.5 divisions
threshold = 0 mV
polarity = Both
range of n
low n = 3
high n = 11
period = 231.5 ns.
F1 is defined as a zoom of channel 1 so that the waveform can be viewed expanded and the pits
and spaces can be identified.
Using the Math Setup dialog, F2 is defined as the histogram of the pwid parameter on P1 and is
set up as follows:
5T
1.16
µs
3T
694
ns
3T
696
ns
voltage
threshold
4T
925 ns