Serial I/O Description; Figure 4-1: Differential Amplifier - Xilinx RocketIO User Manual

R
Analog Design Considerations

Serial I/O Description

The RocketIO transceiver transmits and receives serial differential signals. This feature
operates at a nominal supply voltage of 2.5 VDC. A serial differential pair consists of a true
(V
transferred data. Thus: V
crossing of the two complementary signals. Therefore, no separate reference level is
needed.
A graphical representation of this concept is shown in
The RocketIO transceiver is implemented in Current Mode Logic (CML). A CML output
consists of transistors configured as shown in
offers easy interface requirements. In this configuration, both legs of the driver, V
sink current, with one leg always sinking more current than its complement. The CML
output consists of a differential pair with 50Ω (or, optionally, 75Ω) source resistors. The
signal swing is created by switching the current in a common-drain differential pair.
The differential transmitter specification is shown in
UG024 (v1.5) October 16, 2002
RocketIO™ Transceiver User Guide
) and a complement (V
P N
– V
P
www.xilinx.com
1-800-255-7778
) set of signals. The voltage difference represents the
= V . Differential switching is performed at the
N DATA
CML Output Driver
U024_06_020802

Figure 4-1: Differential Amplifier

Figure
Chapter 4
Figure 4-1.
DATA
4-1. CML uses a positive supply and
Table 4-1, page 84.
and V ,
P N
83