352 Keysight M8000 Series of BER Test Solutions User Guide
6 Setting up Analyzer
Bit Recovery Mode
Understanding Bit Recovery Mode (BRM)
Traditionally, bit error rate testing compares the bits from a Device Under
Test (DUT) against a reference data set, called the expected data. The user
of Bit Error Ratio Tester (BERT) has to provide this expected data and load
it into the M8020A/M8030A.
The M8020A/M8030A system then samples the incoming data signal with
a sampling point that can be varied over time and voltage, to measure the
BER. The M8070A system software is capable of creating graphics, such as
the eye opening, from the information gathered during sampling. A
compare circuit counts the differences between the bits of the incoming
data stream and the expected data.
Now there is a mode that removes the need for the user to provide
expected data, while still allowing one and two-dimensional
measurements, such as the eye opening.
This is the Bit Recovery Mode (BRM).
This has two benefits:
• the user does not need to worry about the expected bits, which makes
a setup easier and faster.
• the M8020A/M8030A system can measure non-deterministic data
streams. This means it is no longer necessary to force a device into a
specific test mode.
Bit recovery mode uses a second sampling circuit in the M8020A/M8030A
analyzer to always sample at the sweet spot of the eye (typically at 50% of
eye opening in time and voltage). The sampled data from this second
sampling circuit acts as a reference and is passed to the compare circuitry,
instead of the expected data.
This means the BER is now a relative figure. Taking the bit from the sweet
spot of the eye cannot verify if this bit is correct in itself, it can just use it as
a reference for any bit sampled in the border area of the eye. Bit recovery
mode makes one and two-dimensional sweeps possible to sample in the
border area of the eye and find out how the BER value increases. From this
The M8040A analyzer (M8046A) does not support bit recovery mode.
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