Teledyne LeCroy QPHY-DDR4 - Manual (Page 59)

QPHY-DDR4 Software Option
tHZ/tLZ, High/Low Impedance Time
The purpose of this test is to characterize the High and Low Impedance times. These tests are measuring
the timing between when the device quits driving (tHZ) or begins driving (tLZ) and CK at Vref. tHZ only
tests the maximum value and tLZ tests both a minimum and a maximum value. These tests are measured
on both DQ and DQS. 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 tHZ(DQ) will be discussed below. The only difference between tLZ and tHZ is begin
driving vs when the device quits driving. tLZ measures the time from when DQ/DQS begin driving
from CK. tHZ measures the time from when DQ/DQS quits driving from CK. The measurement
methodology is the same for the DQS.
After the completion of the tLZ(DQ) test the oscilloscope is in the following configuration:
Figure 49 - Oscilloscope Configuration after the tLZ(DQ) 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” tHZ measurement indicated by t@tHZmax. A trace
label is applied on this trace at Vref.
• 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” tHZ measurement indicated by t@tHZmax. This
signal is not measured in this test and is only provided as a visual reference.
• Z3 is a zoom of F3, the acquired DQ signal after any probe deskew has been applied. The zoom is
position at the location of the “worst case” tHZ measurement indicated by t@tHZmax. A trace
label is applied on this trace according to the signal name assigned to DQ to indicate where the
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