Lambda SR1, Руководство по эксплуатации, Страница: 188 / 317

SR1 Operation Manual 188
© 2014 Stanford Research Systems
To account for these processes the digitizer includes an "asymmetry" parameter when reconstructing
the original clock. Instead of a single Unit Interval length, the digitizer assumes 2 unit interval lengths,
one for positive pulses and one for negative pulses. The difference in the lengths of positive going pulses
(U
+
), and negative going pulses (U
-
), is calculated and displayed as an "asymmetry" parameter defined
as:
asymmetry = (U
+
– U
-
)/(U
+
+ U
-
)
The asymmetry calculated for each input record is displayed on the "Advanced" tab of the digitizer
panel.
If desired, the "peak-splitting" produced by asymmetry in the input record can be removed before
calculating the pulse width histogram by checking the "Rise/Fall" checkbox on the "Advanced Measure"
tab of the digitizer panel. When the box is checked the digitizer will "correct" the measured pulse widths
by the calculated asymmetry before compiling the pulse-width histogram. The histogram above, when
recalculated with "Rise/Fall" checked yields the result shown below.
Additional Analysis Controls
The "Re-analyze" button causes the digitizer to reanalyze the current digitizer record, with possibly
different analysis settings, without first acquiring a new record. The "Fast Interpolation" check box
selects the use a faster, but less accurate interpolation algorithm (spline interpolation) when calculating
the zero-crossing positions in the input record. The standard interpolation algorithm (band-limited
interpolation) yields the highest accuracy.
Digitizer Measurements
The input amplitude vs. time and jitter amplitude vs. time measurements are always calculated by the
digitizer. Optionally three additional sets of measurements can be selected. If these additional
measurements are not needed, the corresponding check boxes may be left unchecked to save
computation time.
Checking the "Spectrum" box instructs the digitizer to compute the FFT of the input signal and the jitter
spectrum. The window function applied before calculating the spectra can be selected from the same list
of window functions available in the
FFT analyzers . The spectral resolution for the input amplitude
spectrum can be selected between 512 and 16k lines. The number of lines in the Jitter spectrum is