Output Swing And Emphasis; Emphasis; Chapter 4: Analog Design Considerations - Xilinx RocketIO X User Manual

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Output Swing and Emphasis

The output swing and emphasis levels of the RocketIO X MGTs are fully programmable.
Each is controlled via attributes at configuration, but can be modified via partial
reconfiguration or the PMA attribute programming bus
Programming
Note:
silicon-based tables.

Emphasis

With 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 emphasis
are shown in four scope screen captures,
Definition" in Appendix C
Figure 4-5
data. The STRONG notation in
voltage magnitude, at this point, than the LOGIC or normal level (LOGIC level is the level
with no emphasis).
A second characteristic of RocketIO X transceiver 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 emphasis
technique extends the distance that signals can be driven down lossy line media and
increases the signal-to-noise ratio at the receiver.
Emphasis can be described from two perspectives, additive to the smaller voltage (V
(pre-emphasis) or subtractive from the larger voltage (V
benefits in compensating for channel loss are identical. It is simply a relative way of
specifying the effect at the transmitter.
The equations for calculating Pre-Emphasis as a percentage and dB are as follows:
The equations for calculating De-Emphasis as a percentage and dB are as follows:
92
Bus").
Table 4-2 through Table 4-5
for the signal or attribute Effects.) Note that
are for illustration purposes only and do not correspond to actual RocketIO X
Pre-Emphasis = ((V
% LG
Pre-Emphasis = 20 log(V
dB
De-Emphasis = (V - V
% LG
De-Emphasis = 20 log(V
dB
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Chapter 4: Analog Design Considerations

are based on simulation only. See the Characterization Report for
Figure 4-2 through
Figure 4-3 is used to show that the waveform is greater in
-V ) / V ) x 100
SM SM
/V )
LG SM
) / V ) x 100
SM LG
/V )
SM LG
(Appendix C, "PMA Attribute
Figure 4-5. (Also, see "Register
Figure 4-2
) (de-emphasis). The resulting
LG
RocketIO™ X Transceiver User Guide
UG035 (v1.5) November 22, 2004
through
)
SM