Agilent Technologies 71612, Quick Reference

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BER Basics
Bit Error Ratio (BER) is the most fundamental measure of
system performance - how well bits are transferred end-to-
end. While this performance is affected by factors such as
signal-to-noise and distortion, ultimately it is the ability to
receive information error-free that defines the quality of
the link.
A Bit Error Ratio Tester (BERT) measures BER on
systems and components. Usually BERTs are made of two
components, the Pattern Generator (PG) and the Error
Detector (ED). They can provide test data sequences, and
also measure error ratio. Often the two components are
used together, but not always - a PG makes an ideal
stimulus for component design work. In some BERTs, the
clock source may also be separate.
A BERT makes physical layer measurements and differs
from a protocol or SONET tester in the following ways. A
BERT can usually:
• Vary voltage levels.
• Vary the timing relationship between clock and data.
• Vary the clock frequency significantly.
See over the page for a block diagram showing a Pattern
Generator and Error Detector.
BER =
=
Number of bits received in error
Number of bits received
Error count in measurement period
(Bit rate) x (measurement period)
BER -
What is it?
71612-90017.fm Page 43 Wednesday, July 18, 2001 11:26 AM