User guide

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