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Chapter 12: PCB Materials and Traces
Simulating Lossy Transmission Lines
Due to the different modeling implementations used by various circuit simulators,
frequency-domain versus time-domain techniques, it is important to check that the models
accurately reflect actual losses. One method is to compare the models against known
published configurations.
Cable
Cables are controlled-impedance transmission lines due to the constant physical
dimensions of conductor and dielectric along the length of the cable. The highest quality
cable shows little variation in these dimensions and also has a wide bandwidth with low
loss at high frequencies.
Connectors
The connectors attached to cables should exhibit low parasitic inductance and capacitance
for high bandwidth operation.
Optimal Cable Length
Xilinx provides cable characterization reports of CAT5/5E/6, Infiniband HSSDC2, and
Serial ATA for designers to select the appropriate cable type based on performance at
various lengths.
Skew Between Conductors
When selecting a cable, look for a specification of the skew between the conductors in a
cable. If the conductors are not length matched, the skew appears in the common mode
and directly reduces the eye height.
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Virtex-5 RocketIO GTP Transceiver User Guide
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UG196 (v1.3) May 25, 2007
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