Why do I need a BERT?
A Bit-Error-Rate-Tester is required to test an optical or electrical link
performance on a physical level. Bit-errors occur at receivers when low
input signal are disturbed by its internal noise. Thus a receiver is
characterized by its input sensitivity given in bit-error-ratio at a defined
input signal level. This cannot be tested by oscilloscopes,
network analyzers or protocol analyzers.
What is the benefit of LUCEO's BERT in manufacturing test of SFP and XFP modules?
Testing SFP+ and XFP modules in production requires a lot of test devices.
Most test-equipment is designed for R&D requirements. LUCEO's platform
provides all optical and electrical functionalities to perform full
production test without spending money for unused functionality.
What is GUI?
The GUI (Graphical-User-Interface) is a PC based software to control
the X-BERT mainframe, plugged modules and to display measurement results.
It supports multi-channel application as well, e.g. displaying the
bit-error-ratio of the link over all used channels.
What is the purpose of gating?
Gating is necessary to measure down to low levels of bit-error-ratio,
e.g. 10-12. It counts for a given time received bits and bit errors.
Because bit-errors don't occur at a predictable time, a sufficient
gating-time must be chosen to get reliable statistical results. A weak
statistic is 10 errors. To see pattern dependant penalties 100 errors
or more are recommended.
How to use error injection (insertion)?
Error injection generates a bit error at the pattern generator that should
be seen at the error-detector. If coding functionalities (8B/10B or 64B/66B),
clock-data-recoveries or error compensation circuitries are used in the data
path it might happen that these chips struggle at bit errors even if their
overhead or synchronization patterns were hit. In such cases it may result
in higher bit-error-ratio then generated by the pattern generator, due to
bit position jumps, loss of lock or sent error codes. To make repeatable
measurements the pattern generator provides an error injection at a selectable
error ration, e.g. 10-3. Single errors may also be injected to observe single events.
When to use Pre-Emphasis ?
Pre-Emphasis is a kind of pre-distortion that amplifies higher frequency portions
of the signal spectrum. It is used to compensate losses causes by components with
very limited bandwidth in the data path. Such losses are caused by FR-4 boards,
RF-cables with insufficient bandwidth or amplifiers stages with insufficient bandwidth.
What is invert data out for?
In some cases setups don't run because of swapped data polarity.
This can happen in complex setups by swapped cables, inverted modulation
(current push or current pull) or errors in chip configurations. However,
the pattern generator output provides a differential output DOUTP/N. The
polarity can be swapped by GUI software. This eases the identification
of basic polarity errors in a setup.