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Differential TDR Measurements
Differential TDR Features
Differential TDR Features
The HP 54754A TDR plug-in module is capable of performing differential TDR
measurements. These measurements include characterizing differential
microstrip lines, differential PC board traces, and differential cables. Because
differential TDR measurements are complex, the differential TDR plug-in
module has several features which make measurements easier.
The Preset TDR/TDT Feature
The Preset TDR/TDT feature prepares the oscilloscope for making TDR and
TDT measurements by automatically setting several menu fields. The Preset
TDR/TDT feature appears in the TDR/TDT Setup menu once a stimulus has
been selected.
Differential and Common Mode Stimulus Feature
The feature allows you to deliver to a TDR system either differential or common
mode stimulus. Differential stimulus launches a positive going step on channel
1 and an effective negative going step on channel 2. Common mode stimulus
launches a positive going step on both channels.
Responses to Differential and Common Mode Stimulus
Response controls are provided which show the differential or common mode
response of a TDR system under test stimulated by differential or common mode
stimulus. It is also possible to view the individual channels responses.
TDR Channel Deskewing Feature
Before accurate differential or common mode TDR measurements can be made,
it is necessary to deskew the two TDR step generators. Under the channel menu
for each TDR channel there is a Calibrate . . . softkey. When this softkey is
selected, it allows you to enter a channel Skew and a TDR skew parameter.
Channel Skew is a feature that allows the acquired signal to be moved in time
with respect to other acquired channels. Since sequential sampling
oscilloscopes do not have negative time, this control only allows waveforms to
be moved to the left or more positive in time. This control is used in deskewing
differential TDR and in normal signal acquisition applications.
TDR skew is a feature that allows positioning of the actual TDR step. It has an
approximate range of ±400ps. The units of the control are in % of the maximum
range of ±100%. This control moves the position of the TDR step whereas the
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