Keysight M8000 Series of BER Test Solutions User Guide 481
Working with Measurements 8
Random and Deterministic Jitter
To understand the RJ and DJ results, it is helpful to first understand how
the software generates the results:
1 The bathtub curve is measured.
2 All measurement points that have BER between the BER Threshold and
Minimum BER for RJ/DJ Separation are transformed into Q-space.
The Q-factor describes the signal-to-noise ratio at the decision circuit.
3 Linear regression is performed for both the left and right edges.
4 The mean and sigma are calculated for both lines:
• RJ is calculated as the mean of the two sigmas.
• DJ is calculated as the period minus the difference of the two
means.
5 The estimated TJ is calculated:
• Linear regression is used to extrapolate the bathtub curve to lower
BER values.
• The intersections of the resulting lines with the Residual BER for
RJ/DJ Separation are located.
• The eye opening is calculated.
The estimated TJ is the period minus the width of the eye opening.
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