Agilent Technologies J-BERT N4903, User Manual

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The Serial BERT's clock cannot be used for bit rates below 620 Mb/
s.
Bit Rate Range
The Serial BERT provides bit rates from 150 Mbit/s up to 12.5 Gbit/s,
depending on the instrument's options.
However, several specific properties and limitations need to be taken
into account when working at low bit rates. The limitations apply to the
instrument according to the following hysteresis curve:
•
If the bit rate falls below 615 Mbit/s, the limitations apply.
•
If the bit rate exceeds 620 Mbit/s, the limitations no longer apply.
The following figure clarifies the behavior in the range between
615 Mbit/s and 620 Mbit/s:
615 Bitrate [Mbit/s]
620
Limitations do not apply
in this range
Limitations apply
in this range
For the pattern generator the following rules apply:
• Below 620 Mbit/s, the pattern generator can only be operated with
an external clock source, because the internal clock source can only
produce signals higher than 620 Mbit/s.
• The trigger output cannot be set up to trigger on certain pattern
positions or pattern sequences. If this option is enabled (for example
in the user interface), the trigger is sent once for each pattern, but
the bit position cannot be specified.
The option to trigger on the divided clock signal is supported as
usual.
• There are restrictions to the available clock to data delay values.
The pattern generator can vary the clock to data delay only within a
range of -750 ps to 750 ps (relative to the clock signal). For
frequencies above 666 Mbit/s, this range is sufficient to cover the
complete clock cycle (= 1 unit interval).
For lower frequencies, the valid data delay range is smaller than the
clock cycle. The pattern generator cannot generate signals with a
3
Setting up the Pattern Generator
88 Agilent J-BERT N4903 High-Performance Serial BERT