Operating Manual Vol 1 - ES Documentation

SMIQBit Error Rate TestPossible Problems with BER Measurement and Related SolutionsFault Possible cause Fault description/remedyBERmeasurementdoes notsynchronizeNo signals received fromDUT or the signal level isnot correct.The selected PRBS is notcorrect.A wrong clock edge isused, which violates setupor hold times. Check displays for activity at BER measurement inputs.If a status is displayed (Clock, Data, Sync) for a line, there isactivity.Normally, the PRBS on which the data are based is used as thedefault setting. If the PRBS is changed, the BER measurementcannot synchronize to the data (because the polynomial is notcorrect). Check the bit clock signal, the data signal and the data enablesignal, if any, on an oscilloscope.The fault may also be caused by reflections on the clock line, whichswitch the data signal twice into the BER measurement, eg on lineswithout termination. The SMIQ input is not terminated.Incorrect polarity of datasignal (or data enablesignal).In this case the PRBS cannot synchronize. Note that an inversionof the output signal specified for some cases by the PRBSstandard is performed automatically upon PRBS selection.Manual inversion of the data signal is therefore not required.A bit error occurs duringsynchronization (nine databits with PRBS9)The BER measurement is started at a wrong position so thatabout 50% of the subsequent data bits are identified as faulty.No clock receivedfrom DUTMeasured BERtoo highWhen testing RFcomponents, clockrecovery is not available.An external clock ishowever required forclocking the data during theBER measurementThe data are clocked withthe wrong edge and/or theeye aperture of the data isnot optimally met.Instead of a clock recovery circuit, the bit clock at the PAR-DATAconnector of the SMIQ may be possibly used as a replacement.This is possible if DGEN (SMIQB11) is used as a data source.However, this bit clock is not possible with all modulation types.Also, the delay between data and clock has to be observed. Check the clock/data relationship by means of an oscilloscope andset optimum timing..BER measurement doesnot synchronizeIf data that are not cyclically continued (ie when a break occurs at thememory wrap-around), the measurement will identify about 50% of thebits as faulty after the wrap-around.Make sure the measurement is started optimally at the beginning of thesequence by means of a signal on the REStart line (see: "BERmeasurement with interrupted random sequence – integrating BERmeasurement" in section 2.23.1.3, "Test Method").1125.5555.03 2.377 E-9