High Speed Twisted-Pair Transmission
Data rates up to 100Mbps can be transmitted over short
distances using Category 5 UTP (unshielded twisted pair).
The cable distance will determine the maximum data rate.
Figures 11 and 12 show an 8ns pulse propagating over 25
feet of Category 5 UTP. Notice how the cable attenuates the
signal. Lucent Technologies’ BRF2A and BRS2A receivers
are recommended for these ultrahigh speed applications.
High Speed Backplane Transmission
The LTC1688/LTC1689 can be used in backplane point-to-
point and multipoint applications. At high data rates,
signals should be routed differentially and PC traces
should be terminated (see Figure 13). Note that the RS485
specification calls for characteristic impedances near 100Ω;
therefore, PC trace transmission lines should be designed
with an impedance close to 100Ω. If trace impedance is
much less than 100Ω, and the trace is double terminated,
the part will experience excess heating. The propagation
delay could then fall outside the specified window. The
LT1720 dual UltraFast
comparator is a good choice for
high data rate backplane applications.
Figure 12. 100Mbps Differential Data Connection
Figure 11. 8ns Pulse Over 25 Feet Category 5 UTP
25 FT CATEGORY 5 UTP
Figure 13. 100Mbps Backplane Transmission
UltraFast is a trademark of Linear Technology Corporation.