Chapter 4: Pma Analog Design Considerations; Serial I/O Description; Differential Transmitter; Output Swing And Emphasis - Xilinx Virtex-4 RocketIO User Manual

R
PMA Analog Design Considerations

Serial I/O Description

The RocketIO Multi-Gigabit Transceiver (MGT) transmits and receives serial differential
signals, using a nominal termination supply voltage of 1.5 VDC. A serial differential pair
consists of a true (V
represents the transferred data. Thus: V
performed at the crossing of the two complementary signals so that no separate reference
level is needed. A graphical representation of this concept is shown in

Differential Transmitter

The RocketIO transceiver is implemented in Current Mode Logic (CML). A CML
transmitter output consists of transistors configured as shown in
a positive supply and offers easy interface requirements. In this configuration, both legs of
the driver, V
complement. The CML output consists of a differential pair with 50Ω source resistors. The
signal swing is created by switching the current in a common-source differential pair.
The differential transmitter specifications are shown in the RocketIO DC Specifications and
the RocketIO Transmitter Switching Characteristics in the Virtex-4 Data Sheet.

Output Swing and Emphasis

The output swing and emphasis levels of the MGTs are fully programmable. Each is
controlled via attributes at configuration, but can be modified via the Dynamic
Reconfiguration Port programming bus
Virtex-4 RocketIO MGT User Guide
UG076 (v4.1) November 2, 2008
) and a complement (V
P
CML Output Driver
Figure 4-1: Differential Amplifier
and V , sink current, with one leg always sinking more current than its
P N
www.xilinx.com
) set of signals. The voltage difference
N
V = V . Differential switching is
P –
N DATA
V
P
V V
V
- =
DATA
P N
V
N
U035_06_091903
Figure
(Appendix C, "Dynamic Reconfiguration
Chapter 4
Figure 4-1.
4-1. The CML uses
Port").
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