Skew Measurements Of Differential Signals - Tektronix TriMode TDP7700 Series Technical Reference

Theory of operation
Skew measurements of
differential signals
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Figure 22: Active tip measurement configuration
Differential signals are composed of two complementary single-ended signals
that generally swing around a common bias voltage. An example of an LVDS
differential signal is shown in the following figure.
Figure 23: Example of LVDS differential signal
The complementary single-ended signals labeled A and B in the previous figure
must have well matched signal timing (for example, low skew) to function as a
useful differential signal. If the signal skew becomes comparable in size to the
rise time of the complementary signals, then the rise time of the resulting
differential signal will be slower than expected. Skew is a measure of the time
delay mismatch between two supposedly matched signals.
Although very accurate low skew measurements usually require TDR or VNA
measurement equipment, it is possible to make relatively accurate skew
measurements of a differential signal pair using a TDP7700 Series probe and a
TekFlex probe tip. A flex circuit based solder tip should first be soldered to the
DUT differential signal, taking care to match the A and B input wire lengths,
because the wiring length mismatch will contribute to the skew measurement
error. A DUT ground reference connection should also be made to one of the
TekFlex tip ground vias using a wire length as short as possible.
TDP7700 Series TriMode Probes Technical Reference