Agilent Technologies J-BERT N4903B, User Manual, Page: 140 / 572

The Serial BERT can be connected to an external clock to allow it to run as part
of a larger external system.
• Use of a modulated clock
A frequency- or delay-modulated clock can be used to provide a small amount
of jitter to the clock signal.
• Use of a precision clock
A precision clock with very low phase noise can be used to enhance the
instrument's performance. This is especially interesting for long-term
measurements.
• Testing at bit rates < 620 Mb/s
The Serial BERT's internal 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.
N O T E
The "Bit Comparison without USB3.1 SKPOS" error ratio mode supports the bit rate
up to 10.35 Gbit/s. However, if you want to use bit rate greater than 10.35 Gbit/s
then switch to "8B/10B Symbol Comparison" or "Bit Comparison without PCIe3
SKPOS" error ratio mode and then go to "Bit Comparison" mode. For details, refer
to
“Setting up Error Ratio” on page 185 .
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
4
Setting up the Pattern Generator
140 Agilent J-BERT N4903B High-Performance Serial BERT