LeCroy DDA 7 Zi series, Operator'S Manual

Page: 318 / 544

WavePro 7Zi
317
WP700Zi-OM-E-RevA
Example 1
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:
1. Use the maximum number of values (2,000,000,000)
2. Classify into 2000 bins
3. Linear vertical scale.
The trigger is set up to trigger on a pit edge and operated in normal trigger mode.
Note: Prior to acquisition, select each trace and press the RESET button to ensure that all the traces are reset.