Pre-Emphasis Techniques; Table 4-1: Differential Transmitter Parameters; Table 4-2: Pre-Emphasis Values - Xilinx RocketIO User Manual

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Table 4-1: Differential Transmitter Parameters

Pre-emphasis Techniques

In pre-emphasis, the initial differential voltage swing is boosted to create a stronger rising
or falling waveform. This method compensates for high frequency loss in the transmission
media that would otherwise limit the magnitude of this waveform. The effects of
pre-emphasis are shown in four scope screen captures,
the pages following. The STRONG notation in
waveform is greater in voltage magnitude, at this point, than the LOGIC or normal level
(i.e., no pre-emphasis).
A second characteristic of RocketIO transceiver pre-emphasis is that the STRONG level is
reduced after some time to the LOGIC level, thereby minimizing the voltage swing
necessary to switch the differential pair into the opposite state.
Lossy transmission lines cause the dissipation of electrical energy. This pre-emphasis
technique extends the distance that signals can be driven down lossy line media and
increases the signal-to-noise ratio at the receiver.
The four levels of pre-emphasis are shown in

Table 4-2: Pre-emphasis Values

84
Parameter
V Serial output differential
OUT
peak to peak (TXP/TXN)
V Output termination
TTX
voltage supply
V Common mode output
TCM
voltage range
V Differential output skew
ISKEW
Attribute Values Emphasis (%)
0
1
2
3
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Chapter 4: Analog Design Considerations
Min Typ Max Units
800 1600
1.8 2.8
1.5 2.5
15
Figure 4-2
Figure 4-3
Table 4-2.
10
20
25
33
RocketIO™ Transceiver User Guide
Conditions
mV Output differential
voltage is program-
mable
V
V
ps
through Figure 4-5
is used to show that the
UG024 (v1.5) October 16, 2002
on