Teledyne LeCroy QPHY-DDR4 - Manual (Page 48)

• 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@tVACmin (P4) displays the location of where the minimum value of tDVAC occurred. This is used
to position the zoom traces at the location of the “worst case results”.
• Slew(z1) is measuring the slew rate on the rising edge of CK at t@tVACmin from Vref to VIH(ac).
This value is used to determine the appropriate limit for tDVAC.
AC Overshoot/Undershoot
The purpose of this test is to characterize the overshoot above VDDQ and undershoot below VSSQ on
DQ, DQS, and CK during W bursts. Both peak amplitude and area are tested.
Note: Only overshoot of DQ will be discussed below. The measurement methodology is exactly same
for the DQS and CK. The measurement methodology is also identical for undershoot except VSSQ is
used instead of VDDQ.
Peak Amplitude
After the completion of the Overshoot Peak Amplitude test the oscilloscope is in the following
configuration:
Figure 35 - Oscilloscope Configuration after Overshoot Peak Amplitude Test
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