Tektronix OM4006D, User Manual

Page: 57 / 205

Operating basics
The following controls are relevant to both equivalent-time and real-time
oscilloscopes except where noted.
Table 11: OUI: Analysis Parameters window
Parameter Description
Signal type Sets the type of signal to be analyzed and the algorithms to be
applied corresponding to that type.
Pure phase modulation Sets the clock recovery for when there is no amplitude
modulation.
Clock frequency
(Nominal, Low, High) The nominal frequency of the clock recovered by CoreProcessing
bounded by a low (Low) and a high frequency (High), provided
the clock signal power is suf
fi cient.
Time offset Applies an offset in time (horizontal movement on the eye
diagram) to the signal. If a signal has structure, e.g. ringing,
then the clock recovery process may give a result away from the
symbol center. The Time offset adjustment can move it back.
Lowpass fi lter If the edges of a signal are steep or if there is some ringing then
the clock recovery process may give an eye diagram displaced
from the symbol center. Switching on the lowpass
fi lter may
cause the eye diagram to become centered. The lowpass fi lter is
applied in the clock recovery path; it does not affect the signals
seen in the OUI plots.
Apply limiting function Some signal distortions may cause the clock component of the
signal to be weak, so that the eye diagram is shifted in time or
the clock recovery fails (wrong frequency reported). Switching
in the limiting function may correct these issues. The limiting
function is applied in the clock recovery path, and does not affect
the signals seen in the OUI.
Limiter threshold
Threshold level for clock recovery limiting function. A low
threshold applies steeper limiting, but may require a longer
record length.
Assume Orthogonal
Polarizations Checking this box forces Core Processing to assume that the
polarization multiplexing is done in such a way that the two
data signals have perfectly orthogonal polarization. Making this
assumption speeds processing since only one polarization must
be found while the other is assumed to orthogonal. In this case,
the resulting SOPs will be a best effort
fi t if the signals are not in
fact perfectly orthogonal. Unchecking the box forces the code to
search for the SOP of both data signals.
Reset SOP Each Block
(RT oscilloscopes only) Checking this causes the SOP to be recalculated for each Block
of the computation. By adjusting the Block Size (see Blk Size)
you can track a changing polarization. When false, the SOP is
assumed constant for the entire Record (see Rec Len).
OM4000D Series Coherent Lightwave Signal Analyzer 33