Teledyne LeCroy QPHY-DDR4 - Manual (Page 47)

QPHY-DDR4 Software Option
tDVAC, Time Above AC Level
The purpose of this test is to verify the allowed time before ringback for the differential CK signal. It is
measured as the time above the VIH(ac) level and below the VIL(ac) level. This clock signal is only
measured when a W burst has been detected.
Note: Only tDVAC measured on above VIH(ac) will be discussed below. The measurement
methodology is exactly same for below VIL(ac).
After the completion of the tDVAC test the oscilloscope is in the following configuration:
Figure 33 - Oscilloscope Configuration after the tDVAC 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
positioned at the location of the “worst case” tDVAC measurement indicated by t@tVACmin. A
trace label is applied on this trace according to the signal name assigned to CK and placed at the
VIH(ac) level.
Figure 34 - tDVAC Results
In the Measure section:
• tVACvih (P1) is measuring the time above VIH(ac) for CK. VIH(ac) is indicated by the trace label
“CK at VIH(ac)”. The minimum value is the measured value for tDVAC min of CK. Since the limit
in the specification is undefined this test is Informational Only.
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