Figure 11.12: Cross-section view of two different PCB boards connected by a typical
connector along with the simple model.
Figure 11.13: The TDR response for two different edge rates illustrates the resolution
difference on the connector lumped elements.
Incident Characteristics.
The inherent TDR response characteristics, such as settling time, foot, and preshoot (see
Figure 11.11
), are also important to consider with respect to TDR resolution. The incident
response characteristics are essentially the difference between the ideal and actual step
response. The foot and preshoot refer to the section of the response prior to the vertical
edge, while settling time is the time for the response to settle.
These characteristics are inherent in the incident wave and will affect the resolution of the
measurement. A simple example of this can be illustrated with the settling time. If the settling
time is long compared to the electrical delay of the structure being measured, it may induce
false readings because the impedance measurement might be taken at a peak or dip in the
response. This would look like an impedance variation when in reality it is simple inherent
ringing in the response. Possible methods to minimize these effects are covered in the
following section.
Summary :
The inherent TDR response characteristics, such as settling time, foot, and preshoot (see Figure 11.11 ), are also important to consider with respect to TDR resolution. The foot and preshoot refer to the section of the response prior to the vertical edge, while settling time is the time for the response to settle.
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response,time,characteristics,settling,incident,inherent,figure,simple,resolution,tdr,section,preshoot,difference