Teledyne LeCroy QPHY-DDR4 - Manual (Page 62)

In the Measure section:
• tRPRE (P1) is measuring the time from when time DQS quits driving to the next rising edge on DQS
at Vref. The idle quit time is indicated by the trace label which is found through interpolation.
Essentially the time between the two trace labels is measured. The minimum value is the
measured value for tRPRE min reported in mtCK(avg). This test is considered informational only
since the limit is undefined.
• tDQDQS (P2) is measuring the skew between DQ and DQS. Since this measurement is performed
once per burst, this shows how many R bursts were in the acquired waveform.
• t@tRPREmin (P4) displays the location of where the minimum value of tRPRE occurred. This is
used to position the zoom traces at the location of the “worst case results”.
tDQSS, CK to DQS Skew
The purpose of this test is to characterize the allowed range for a rising DQS edge relative to CK on W
bursts. This measures the time from
CK rising at Vref to the nearest DQS rising at Vref. Both the maximum and
minimum values are measured. This test is very similar to tDQSCK, which is measured on R bursts.
After the completion of the tDQSS test the oscilloscope is in the following configuration:
Figure 53 - Oscilloscope Configuration after the tDQSS test
Shown on this screen:
• Z1 is a zoom of F1, the acquired CK signal after any probe deskew has been applied. The zoom is
position at the location of the “worst case” tDQSS measurement indicated by t@tDQSSmax. A
trace label is applied on this trace at Vref.
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