Pre-Emphasis - Xilinx Virtex-5 RocketIO GTP User Manual

Chapter 6: GTP Transmitter (TX)
Table 6-17: Transmitter Output Swing
Port
TXDIFFCTRL0[2:0] = TXBUFDIFFCTRL0[2:0]
TXDIFFCTRL1[2:0] = TXBUFDIFFCTRL1[2:0]
Table 6-18: Transmitter Pre-Emphasis Settings
Port
TXPREEMPHASIS0[2:0]
TXPREEMPHASIS1[2:0]
Notes:
1. Nominal values. Refer to the Virtex-5 Data Sheet for the exact values.
2. Refer to [Ref 5], pages 211-215 and
Each of the pad drivers is driven by a pre-driver whose output amplitude is controlled by
TXBUFDIFCTRL. Although the pre-driver output swing does not change the output swing
at the TX pad, the inputs of TXBUFDIFCTRL and TXDIFFCTRL must always be tied
together.
Each GTP transceiver includes an additional attribute, TX_DIFF_BOOST, which can be
used to increase the maximum possible output swing. TX_DIFF_BOOST is set to FALSE
when additional output swing is required. TX_DIFF_BOOST is set to TRUE when the
output swing is acceptable and lower power consumption is desired.

Pre-Emphasis

Serial traces tend to attenuate high frequencies more than low frequencies. Pre-emphasis is
a technique used to equalize transmitted data. It compensates for the excess high-
frequency loss by transmitting high-frequency signals with more power than low-
frequency signals.
114
Value
Pre-Emphasis Boost On
TX_DIFF_BOOST = FALSE
2
000
2
001
2.5
010
4.5
011
9.5
100
16
101
23
110
31
111
[Ref 9], pages 465-471 for detailed explanations of pre-emphasis.
www.xilinx.com
Value Transmitter Differential Swing (mV)
000
001
010
011
100
101
110
111
Transmitter Pre-Emphasis (%)
Pre-Emphasis Boost Off
TX_DIFF_BOOST = TRUE (Default Setting)
Virtex-5 RocketIO GTP Transceiver User Guide
1100
1050
1000
900
800
600
400
0
(1,2)
3
3
4
10.5
18.5
28
39
52
UG196 (v1.3) May 25, 2007
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