Bit Rate - Agilent Technologies N4906B Serial BERT User Manual

Setting up the Pattern Generator
64

Bit Rate

Bit rate is defined as bits per second. The pattern generator's clock
rate sets the bit rate and serves as the frequency reference for the
clock and data outputs, your device, and the error detector (if it
receives its clock from the pattern generator). It can be generated
internally or supplied from an external source.
When to Use an External Clock Source?
The Serial BERT's internal clock can be used for most testing
purposes. There are some circumstances, however, when an external
clock source is required:
• Synchronization with an external clock
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 clock cannot be used for bit rates < 620 Mb/s.
Bit Rate Range
The Agilent N4906B 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.
Agilent N4906B Serial BERT, User's Guide, October 2005
Bit Rate