Xilinx RocketIO User Manual page 115

PCB Design Requirements
The RocketIO differential receiver produces the best bit-error rates when its common-mode voltage
falls between 1.6V and 1.8V. When the receiver is AC-coupled to the line, V
determinant of the receiver common-mode voltage, and therefore must be set to a value within this
range. When two transceivers, both terminated with 2.5V, are DC-coupled, the common-mode
voltage will establish itself at around 1.7V to 1.8V.
The V
Table 3-7: V
RocketIO™ Transceiver User Guide
UG024 (v2.3.2) June 24, 2004
TX
Figure 3-16: DC-Coupled Serial Link
and V voltages for different coupling environments are summarized in
TRX TTX
and V
TRX TTX
Coupling
AC
DC
Notes:
1. The recommended voltage for DC-coupled implementations is 2.5V. However, any
voltage is valid as long as both V
specifications shown in Table 3-5, page
Z = 100Ω Differential
0
for AC- and DC-Coupled Environments
V
TRX
1.6V to 1.8V
(1)
2.5V ±5%
and V are the same voltage, and within the
TRX TTX
107.
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RX
UG024_24_042503
is the sole
TRX
Table
V
TTX
2.5V ±5%
(1)
2.5V ±5%
R
3-7.
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