stm7007 STMicroelectronics, stm7007 Datasheet - Page 20

• Manufacturer Part Number: stm7007
• Description: Single-chip Hardware Accelerated Encryption Engine For Computer And Peripherals Applications
• Manufacturer: STMicroelectronics

3.1
20/27
PCB Routing of RX/TX differential signals
Ensure that the board design meets the following criteria:
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To avoid skew, make signal pair lengths equal from the ball to the connector:
TXP length = TXN length, and RXP length = RXN length
Lengths may differ if required to compensate for length mismatch due to poor package
substrate routing.
Route signal pairs in parallel
Ensure a 100Ω differential impedance trace:
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To avoid crosstalk:
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Do not use:
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Make all traces:
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If components (such as AC coupling capacitors) are required on the high speed signal
traces, choose the smallest SMD packages and place them close to connectors.
PCB trace crossing: if two differential traces from different ports must cross, cross the
traces at 90
Route signals on an external layer with a full or partial ground plane layer as the
next internal adjacent layer. A partial ground plane must cover and exceed the
area below the TX and RX signal routing.
Between the package pin and the PCI-Express connectors, ensure equal signal
trace interspace distance on each pair along the entire trace length.
Separate TX and RX pairs a minimum of 5 mm, with no other signals interleaved.
If several ports are routed, do not route the TX and RX traces of each port one
above the other on different layers.
Right angles or 45-degree trace angles; curved traces are preferred
PCB vias
As direct and straight as possible
As short as possible. Signal line attenuation may be compensated for by selecting
a higher buffer swing, but if the largest swing is specified for the application, there
is no capacity for swing compensation.
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(perpendicular) to each other.
Doc ID 022239 Rev 1