Agilent Technologies N4906B Serial BERT User Manual page 93

Clock Setup
Agilent N4906B Serial BERT, User's Guide, October 2005
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.
The following figure clarifies the behavior in the range between
615 Mbit/s and 620 Mbit/s:
615
Limitations apply
in this range
For the error detector the following rules apply:
• For low frequencies, you cannot use the automatic data alignment
functions (Auto Align and Data Center). Instead you need to align
the error detector manually. For instructions, please refer to the
Online Help, go to the Error Detector Setup section, select
Sampling Point Setup, and switch to the Procedures information.
• There are restrictions to the available sampling point delay values.
The error detector can vary the sampling point delay only within a
range of 0 ps to 1.6129 ns (relative to the clock signal). For
frequencies above 620 Mbit/s, this range is sufficient to cover the
complete clock cycle (= 1 unit interval).
For lower frequencies, the maximum sampling point delay is smaller
than the clock cycle. Therefore, the sampling point cannot be set
everywhere within the clock cycle.
Setting up the Error Detector
Limitations do not apply
in this range
620
Bitrate [Mbit/s]
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