Keysight Technologies N5990A User Manual page 50

2 N5990A M-PHY Station
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Bert Analyzer
The DUT is configured in Loopback Mode, so it will loop back the received
test pattern. The Error Detector (ED) then compares the pattern returned
by the DUT with the generated pattern to detect bit errors and compute
the BER.
The pattern must match and be in phase. This is ensured by a common
reference clock. The same pattern is loaded to the generators and the ED.
When the received bits are not synchronized with the pattern of the ED,
the computed BER will be very high. In this case, the synchronization
algorithm in the ED is restarted.
It is important to note that the ED of the BERT compares the whole
pattern, including the Sleep, Stall and Prepare states. This makes
Loopback Mode testing a not very ideal solution for bursted pattern test.
For example, if the Prepare Length that the DUT sends back is different to
that coming from the BERT generator, the computer BER will be high and
the test will fail, even if the returned test pattern matches the original
pattern.
Offline BER Reader
For each step of the test procedure, N5990A shows pop-up dialogs (see
Figure 20, to Figure 22) requesting you to reset and initialize the device
and decide whether the device is working properly. This method is
applicable to devices that allow a visual check, for example, a Display
Serial Interface (DSI) device connected to a display. It is also possible to
connect the DUT to the scope and verify if the output data is valid with
help of the serial decoder. Using an offline BER reader will result in a
semi-automated test where at each test point, you have to enter the pass /
fail information.
Figure 20 MIPI Offline BER Reader Pop-up Dialog 1
Keysight N5990A MIPI M-PHY Receiver Test User Guide