Xilinx RocketIO User Manual page 118

Product Not Recommended for New Designs
R
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
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
Table 3-8: Recommended V
Notes:
1. The recommended voltage for DC-coupled implementations is 2.5V. However,
118
TX
Figure 3-16: DC-Coupled Serial Link
is the sole determinant of the receiver common-mode voltage, and therefore must be
TRX
and V voltages for different coupling environments are summarized in
TRX TTX
3-8.
Coupling
AC
DC
any voltage is valid as long as both V
within the specifications shown in
www.xilinx.com
Chapter 3: Analog Design Considerations
Z = 100Ω Differential
0
and V for AC- and DC-Coupled Environments
TRX TTX
V
TRX
1.6V to 1.8V 2.5V ±5%
(1)
2.5V ±5% 2.5V ±5%
and V are the same voltage, and
TRX TTX
Table 3-5, page 109.
RX
UG024_24_042503
V
TTX
(1)
RocketIO™ Transceiver User Guide
UG024 (v3.0) February 22, 2007