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46 Intel® 41210 Serial to Parallel PCI Bridge Design Guide
PCI Express Layout
9.2 PCI-Express Layout Guidelines
The layout guidelines for PCI-Express were developed for an adapter card topologies. The models and
assumptions used in development of these guidelines were as follows:
• Add-In Card Stackup: 60 Ω single-ended impedance
• Target Differential Impedance: 100 Ω +/- 20%.
• Driver Model: 41210 Bridge PCI-E IBIS
• Receiver Model: 41210 Bridge PCI-E IBIS. Specification model did not meet specifications
• Driver Package Model: Preliminary 41210 Bridge model.
• No receiver package model used since specification eye is at package pin.
• Assumed that traces in a lane could be routed totally on microstrip, totally on stripline, or a
mixture of microstrip and stripline.
• AC coupling capacitors were modeled as a parasitic resistor and inductor in series.
• Add-in card was modeled as micro-strip routes only.
• No vias were modeled at this time.
• Only the receiver eye was evaluated. The next revision will evaluate the eye at the transmitter
and connector as well as the receiver.
9.3 Adapter Card Layout Guidelines
Table 15. Adapter Card Routing Recommendations (Sheet 1 of 2)
Parameter Routing Guidelines
Reference Plane Route over an unbroken ground plane
Target Single Ended
Impedance
60 Ω nominal
Target Differential
Impedance
100 Ω +/- 20% Differential Impedance
Microstrip and Stripline Trace
Width
4 mils
Microstrip Trace Spacing
Intrapair: 10 mils center-to-center
Interpair: 30 mils center-to-center
22 mils. center to center (pair to pair).
Transmit and Receive pairs should be interleaved. If no interleaving, then inter
pair spacing should be increased to 50 mils (c2c). Center to center of inter pair is
defined as center of Positive of one pair to Center of Negative of the next or vice
versa
Group Spacing Spacing from other groups: 25 mils minimum, center to center
Transmit Trace Length
(41210 Bridge signal pin to
AC coupling capacitor.)
0.25”- 5.0” max
Transmit Trace Length (AC
coupling capacitor to card
edge finger.)
1.00”- 4.5” max