Selectio-To-Gtp Crosstalk Guidelines - Xilinx Virtex-5 RocketIO GTP User Manual

Chapter 10: GTP-to-Board Interface

SelectIO-to-GTP Crosstalk Guidelines

Because it is possible for GTP transceiver performance can degrade in an environment
flooded with SelectIO™ activity, it is important to have guidelines for SelectIO usage that
minimize the impact on GTP transceiver performance.
Although the Virtex-5 package exhibits little package-related crosstalk issues, the pinout of
the device might lead to customer designs becoming susceptible to PCB-via related
crosstalk issues. The near proximity of SelectIO signals (aggressor) to GTP transceiver
analog supplies (victim) results in their PCB via structures being placed in close proximity
as well. This ball adjacency and resulting via adjacency creates a via-coupling region
between the SelectIO signals and the GTP transceiver analog supplies that is not filtered by
on-board power supply filtering. The amount of crosstalk voltage induced on the victim
circuit by the aggressor circuit is equal to the rate of change of current in the aggressor
times the mutual inductance shared between the two circuits. For an in-depth discussion
on via crosstalk and calculations of mutual inductance for various via configurations, refer
to High-Speed Signal Propagation: Advanced Black Magic by Howard Johnson and Martin
Graham
from the PCB results in a degradation of GTP transceiver performance. The MGTAVCC
and MGTAVCCPLL supplies are most sensitive to coupled noise.
To minimize the impact on GTP transceiver performance, the following list of BGA
adjacency guidelines must be followed:
•
•
Table 10-5: Aggressive I/O Banks
216
[Ref 5]. The sensitivity of the GTP transceiver analog supplies to coupled noise
Avoid utilizing SelectIO nets 1.0 mm (horizontal or vertical) or 1.4 mm (diagonal)
away from GTP transceiver analog power supply pins. Ground these SelectIO
locations in the PCB, and set the SelectIO output to the highest drive and a forced-Low
setting. If these SelectIO outputs must be used, use them either in differential signaling
applications or for static control/status signals with low speed and low drive.
Avoid using a large number of SelectIO signals in I/O banks near GTP transceivers.
See Table 10-5 for specific aggressive I/O bank to GTP transceiver pairing.
GTP_DUAL
MGT112
MGT114
MGT116
MGT118
MGT120
MGT122
MGT124
MGT126
MGT128
MGT130
MGT132
MGT134
www.xilinx.com
FF665 FF1136
12 12
12 18
12,16 12
12,18 18
12
18
12,20
22
Virtex-5 RocketIO GTP Transceiver User Guide
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18
12
18
12/20
26
12/20
26
20
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UG196 (v1.3) May 25, 2007