EXFO PSO-100 Series Optical Sampling Oscilloscopes - Manual (Page 117)

Optical Sampling Oscilloscope 109
C Measurement Definitions
The measurement definitions essentially follow the conventional standard
from electrical sampling oscilloscopes. All measurements are based on
histograms taken over samples that build up the signal. The measurement
procedure is somewhat different if you are analyzing an eye diagram or
waveform. In eye-mode, the histograms are placed at the same eye in
time, where both a one level and a zero level are present. This is not
possible if a pattern is analyzed. The software then identifies the first rising
and trailing slopes in the window. All parameters (except the fall time) are
then calculated from the rising slope area.
The eye-mode measurements start out by measuring the one and zero
levels since many of the measurement parameters depend on these
values. The one and zero levels are measured according to the figure
below.
The default histogram window width for NRZ data is between 40 % and
60 % of the eye. For RZ, the default window is between 47.5 % and 52.5 %.
These parameters can be changed in the Measure menu, under Window
width.
Note: If you measure on short RZ pulses for example from a ring laser, the 5 %
window width will probably be too wide, and you would need to decrease
the window width.
Measurement window
One level
Histograms
Zero level