Teledyne LeCroy QPHY-DDR4 - Manual (Page 69)

QPHY-DDR4 Software Option
In the Measure section:
• Tdqs (P1) is measuring the setup time from when the rising edge on DQ crosses Vref + (0.5*VdiVW)
to when the rising edge on DQS crosses Vref. Essentially the time between the two trace labels is
measured. The maximum value is the measured value for Tdqs max and is reported in mUI. 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 W bursts were in the acquired waveform.
• t@Tdqsmax (P3) displays the location of where the minimum value of tDSS occurred. This is used
to position the zoom traces at the location of the “worst case results”.
tWPRE/tWPST, Write Pre/Postamble Time
The purpose of these tests is to characterize the Preamble and Postamble times during all W bursts
detected in the acquisition. tWPRE is measuring the timing between when preamble starts (DQS comes
out of idle) and where the preamble ends (DQS at Vref). tWPST 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 tWPST will be discussed below. As stated the only difference between TWPRE and
tWPST is whether the preambles or postambles are measured.
After the completion of the tWPST test the oscilloscope is in the following configuration:
Figure 63 - Oscilloscope Configuration after the tWPST test
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