Teledyne LeCroy TF-DSQ - Manual (Page 19)

TF-DSQ Probe Calibration and Deskew Fixture
TF-DSQ-OM-E RevC 19
Common Mode Voltage Selection
The TF-DSQ fixture calibrates probes differentially or in single-ended mode depending on the
type of probe. Differential probes allow the common mode voltage component to be applied
during the DC calibration for improved calibration accuracy in situations where probe gain or
offset correction depends on common mode components. See
Probe DC Calibration or
Differential and Single-ended Probe Basics for details.
Advanced Probe Calibration
When the Advanced Mode checkbox is checked, you can perform the DC calibration and the
deskew calibration separately by pressing Gain/Offset Only or Deskew Only.
When performing DC calibration, you have the option to apply a common mode component to
the differential DC levels applied to the probe during calibration. See Probe DC Calibration or
Differential and Single-ended Probe Basics for details..
After performing the deskew calibration, you have the option to apply a common skew value to
all channels to adjust the zero time reference of the system.
If you know the risetime of the signals being measured, you can enter the measured risetime of
the signals in the Rise Time field to obtain a further skew correction that accounts for the
risetime. If the risetime entered is less than the risetime measured during the calibration, no
correction is applied; otherwise, the system calculates a correction to account for the signal
risetime. It is important to enter the measured risetime. That is the risetime of the signal that
the oscilloscope measures (or will measure). See details of
risetime correction .
Theory of Operation
Deskew Theory of Operation
Deskewing is an adjustment of the times of waveform data points on the screen. Deskewing is
an operation to correct the times that waveforms are displayed on the screen, mainly to
account for propagation delays through probes and cables.
When considering skew, there are two important things to consider:

The relative skew between two channels

The absolute skew from the zero time reference (i.e., the trigger point)