User guide

With this method you can still place the sampling point anywhere in the clock
cycle to find the optimum sampling point, even at low frequencies.
Clock 310 Mbit/s
Covered Range
3.226 ns
However, if the bit rate falls below appr. 310 Mbit/s, even with this method
gaps occur in the range of possible sampling points.
Clock 150 Mbit/s
Covered Range
with Gaps
6.66 ns
Gap Gap Gap Gap Gap
As a result, you might not be able to find the optimum sampling point, if it falls
in one of the gaps.
Clock Setup - Procedures
To set the clock rate:
1
Press Clock Setup in the ED Setup menu.
2
Specify whether you are using an External Clock Source or Clock Data
Recovery (CDR).
3
If you are using CDR, you need to approximately specify the clock rate in the
Clock Rate field (with an accuracy of 0.01%).
4
If you are measuring bursts, deactivate Auto Threshold and set the threshold
manually. You can also press the Measure button to measure the current DC
level at the CDR input and set the measured value as CDR threshold.
5
Clock rates that are frequently used can be saved as presets in the Preset list.
To select a clock rate from the Preset list, click on it. The clock rate appears in
the Clock Rate field.
6
Specify the Loop Bandwidth within the range of 100 KHz to 12MHz. Specify the
CDR Fine Adjust and Peaking values. When using a Preset, this is only required
when you want to change these values.
7
Enable Spread Spectrum; and adjust the deviation (%) and deviation type as
required.
5 Setting up the Error Detector
178 Agilent J-BERT N4903B High-Performance Serial BERT