Xilinx Virtex-5 RocketIO GTP User Manual

Virtex-5 RocketIO GTP Transceiver User Guide www.xilinx.com 115
UG196 (v1.3) May 25, 2007
Configurable TX Driver
R
The pre-emphasis technique used by the GTP transceiver is de-emphasis. When a serial bit
is repeated, the power of the repeated bit is reduced. For example, if two ones are sent in a
row, the power of the second one is reduced compared to the first. The power of slowly
changing signals (the low-frequency components) is reduced relative to quickly changing
signals (the high-frequency components). Refer to [Ref 4], pages 465-471, and [Ref 5],
pages 211-215, for more detailed explanations of pre-emphasis and de-emphasis.
Each GTP transceiver has a TXPREEMPHASIS port for controlling pre-emphasis.
Table 6-18 shows the percentage decrease of signal amplitude for de-emphasized bits at
each TXPREEMPHASIS level. The higher the percentage, the more de-emphasis is applied.
Be careful not to overcompensate for high-frequency losses. Using too much pre-emphasis
can cause signal distortion, and combining pre-emphasis with RX equalization (see “RX
Termination and Equalization,” page 125) can over-emphasize the high-frequency signal
in the channel.
Configurable Termination Impedance
The termination impedance of each transmitter must be matched as closely as possible to
the impedance of the serial trace it is driving to minimize distortion due to reflections. See
Chapter 10, “GTP-to-Board Interface,” for more information about how the termination
impedance is calibrated.
TXINHIBIT
The TX driver includes the TXINHIBIT port. When TXINHIBIT is driven High, the TX
driver stops sending data and transmits only a differential 0 value (TXP High, TXN Low).

Xilinx Virtex-5 RocketIO GTP Specifications

General

Brand	Xilinx
Model	Virtex-5 RocketIO GTP
Category	Transceiver
Language	English