240 Keysight M8000 Series of BER Test Solutions User Guide
4 User Interface - M8020A Display Views
Therefore, the number of bits per acquisition should be at least as large
that the targeted minimum detectable BER can be achieved. On the other
hand, a large memory size on the oscilloscope side does result in longer
execution times for the signal processing. And this causes latencies
between adjusting a parameter and getting the first BER result that is
based on the new setting and reduces the BER update frequency.
It is best practice to configure the number of bits per acquisition to the
smallest possible value that still results in the desired detectable BER.
Configuring a small number of bits, will result in an instantaneous BER that
becomes more and more insensitive. This is of course causing trouble
when relying on the instantaneous BER result, but it is not much of a
problem for accumulating error ratio measurements, under the premise
that the error distribution is random.
The processing steps within a single acquisition cycle are:
1 The oscilloscope captures the waveform
2 The oscilloscope applies FFE algorithms
3 The oscilloscope applies clock recovery algorithms
4 The oscilloscope applies the decision threshold(s) and extracts digital
symbol information
5 M8070A reads the captured symbols from the oscilloscope
6 M8070A aligns the captured data with the expected data
7 M8070A compares the captured data with the expected data
8 M8070A updates the accumulated and instantaneous error counters
These steps are repeated continuously, and only paused when the
acquisition is stopped, or a parameter value is getting changed.
After step 8, the error count information is available in M8070A, just like for
a hardware based error detector, and is available for measurements.
The currently supported measurements are:
•Error Ratio
• Jitter Tolerance
The currently supported patterns are:
• PRBS 2^n-1
• n = 7, 9, 10, 11, 13, 15, 23, 31, 33, 35, 39, 41, 45, 47, 49, 51
• Memory patterns
• Maximum pattern length = 256 kbit
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