can ALSO be controlled by altering aggressor directionality
Cr osst alk in PCI Ex pr ess
On Microstrip Routing — Interleave TX and RX differential pairs
On Stripline Routing — Interleave RX and TX pairs for long routes — Do not interleave RX and TX pairs for short routes — Use simulation to determine NEXT/FEXT crossover point – Can vary based on length, spacing, stackup – Model different dielectric layers with appropriate dielectric constants – FEXT is not zero
Cont r olli ng Cr osst alk
Space signals further apart — Weaker field interaction
Minimize parallelism — Allows less time for coupled energy to build up — Shorter lengths — Spread out when able
Cont r olli ng Cr osst alk
Minimized through trace spacing — Smaller dielectric heights = less spacing required
Typically good to have at least 3 times the dielectric height for spacing
Should do analysis on signals using a simulator like HyperLynx
Sw eepi ng Tr ace Spacing
Sw eeping Coupli ng Lengt h
Ot her m et hods of noise coupling
Simultaneous switching noise (SSN) — Looks just like crosstalk in the lab – Edge-aligned phenomena
— I/Os switching all at once create excessive power draw which can show up on other signals – Caused by high power distribution network impedance (PDN) – Can be prevented with proper decoupling analysis
Via
noise coupling
— Vias can have mutual inductance and capacitance — Vias radiate noise into plane pairs, which can couple onto other vias and pins
