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Common mode voltage selection, Advanced probe calibration, Theory of operation – Teledyne LeCroy TF-DSQ User Manual

Page 19: Deskew theory of operation, Probe deskew calibration, Deskew calibration, Common mode voltage settings for dc calibration, Tf-dsq probe calibration and deskew fixture

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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)