Single-ended TDR Measurements
Single-ended TDR Features
7-5
Bandwidth Limit
This feature, which is located under waveform math, allows any waveform on
screen to be filtered by a digital low pass filter. This filter is a 4th order Bessel-
Thompson filter. It has no pre-shoot and very little overshoot. The inherent
risetime of the TDR plug-in modules is 35 pS. For many real world systems,
this risetime is much too fast.
Often, it is necessary to test the response of a DUT using a step with a slower
risetime. One way of doing this is to use a TDR normalization filter. This is the
best way because it removes cable losses and discontinuities from the measured
values. It does, however, require that a normalization calibration be performed
at the reference plane. In cases where doing a normalization calibration is
difficult or where the highest degree of accuracy is not needed, the Bandwidth
Limit filter can be used to simulate the DUT with a slower risetime step,
providing good measurement results. In fact, if good quality cables and
connectors are used to connect to the DUT, this method can produce very
similar results to normalization, especially for slower risetimes.
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