R&S AFQ100A Operating Manual page 185

R&S AFQ100A
1401.3084.32
Bit Error Rate Measurements - BERT Block
The measurement is not synchronized.
No Sync
Generally, a measurement cannot be synchronized
until a clock and a data signal have been detected.
If synchronization still does not occur, this may be
caused by the following:
- The selected PRBS is not correct. For the bit
error rate measurement, the PRBS sequence
on which the data is based must be set on the
bit error rate tester. If the PRBS is not correct,
the BER measurement cannot synchronize to
the data (due to the incorrect polynomial).
- A wrong clock slope is used, which violates
setup or hold times (see Clock Slope
parameter).
- The travel times of clock and data are
unfavorable (e.g. clock slope at data change).
Check the relationship of clock to data using an
oscilloscope and optimize the travel times (e.g.
clock slope when the data signal applied is
stable).
- Reflections on the clock line occur, clocking the
data signal into the BER measurement twice,
e.g. on lines without termination. The
instrument input is not terminated.
- Incorrect polarity of data signal (or Data Enable
signal).
In this case the PRBS cannot synchronize.
Note that an inversion of the output signal
specified for some cases by the PRBS standard
is performed automatically upon PRBS
selection. Manual inversion of the data signal is
therefore not required.
No Sync status and an error rate of
approx. 50%:
1. A bit error occurs during synchronization (e.g.
2. If data that is not cyclically continued (i.e. when
4.74
nine data bits with PRBS9). The BER
measurement is set up incorrectly. This fault is
internally detected and automatically
corrected.
a break in the sequence occurs at the memory
wrap-around), the measurement will not be
started at the right time.
The signal on the Restart line enables the
measurement to be started optimally at the
beginning of the sequence.
E-3