Keysight M8000 Series of BER Test Solutions User Guide 243
User Interface - M8020A Display Views 4
Best practices
The following procedure has proven be a reliable way of configuring the
real-time oscilloscope based error detector.
1 Disable acquisition
2 Configure all parameters. Especially the symbol rate and clock
recovery's loop bandwidth are critical to ensure that the clock recovery
will lock.
3 Ensure the signal at the inputs matches the configured parameters.
There are cases when the oscilloscope becomes extremely
unresponsive if the received signal is not matching the configured
parameters. This is mostly caused by misconfiguration of the clock
recovery loop bandwidth, or symbol rate.
4 Run a full auto-alignment and observe the oscilloscope display.
If no eye diagram is shown or warning messages are displayed, then
adjust parameters as suggested by Infiniium.
5 Keep the acquisition depth as low as acceptable.
If there is no need for a specific minimum detectable BER or
confidence level per acquisition, then choose the smallest allowed
value, which depends on the expected pattern selection. This will
ensure better responsiveness of M8070A and increases the BER update
rate.
6 Enable acquisition
Following these steps should ensure that the oscilloscope is
successfully acquiring data and M8070A is therefore able to display
the resulting BER. If this state is reached, then the parameter settings
are good enough to adjust parameters individually. But be aware that
choosing the wrong loop bandwidth setting for the clock recovery can
not only result in errors due to an unlocked clock recovery, but also
have severe impact on processing times of the oscilloscope.
For the best user experience and to avoid common problems that are
caused by incorrect settings, please follow the given recommendations:
• Disable acquisition before doing changes to the incoming signal that
do not match the parameter settings.
Keeping the acquisition enabled while the received signal is in conflict
with the oscilloscope settings, can cause the oscilloscope to get stuck
in processing the signal under wrong parameter configuration.
• Run a full auto-alignment when all parameters are configured, and the
signal is applied to the oscilloscope inputs. But do this before enabling
acquisition on this signal for the first time.
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