Teledyne LeCroy QPHY-DDR4 - Manual (Page 61)

QPHY-DDR4 Software Option
tRPRE/tRPST, Read Pre/Postamble Time
The purpose of these tests are to characterize the Preamble and Postamble times during all R bursts
detected in the acquisition. tRPRE is measuring the timing between when preamble starts (DQS comes
out of idle) and where the preamble ends (DQS at Vref). tRPST is measuring the timing between when
the postamble starts (DQS at Vref) and where the postamble ends (DQS begins to returns to idle). Both of
these test use an interpolation algorithm to determine the point where the signal begins and depending
upon the signal shape this can lead to some inaccuracies.
Note: Only tRPRE will be discussed below. As stated the only difference between TRPRE and tRPST
is whether the preambles or postambles are measured.
After the completion of the tRPRE test the oscilloscope is in the following configuration:
Figure 51 - Oscilloscope Configuration after the tRPRE test
Shown on this screen:
• Z2 is a zoom of F2, the acquired DQS signal after any probe deskew has been applied. The zoom is
positioned at the location of the “worst case” tRPRE measurement indicated by t@tRPREmin. A
trace label is applied on this trace according to the signal name assigned to DQS to indicate
where the interpolation algorithm has determined where the device is no longer idle and Vref.
Figure 52 – tRPRE/tRPST Results
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