EMC and EMI
Electromagnetic compatibility (EMC) is a crucial aspect of high-speed PCB design, ensuring that the device operates reliably
without causing or being affected by electromagnetic interference (EMI). Implementing effective EMC design techniques is
essential to maintain signal integrity and compliance with regulatory standards.
General Solution:
To achieve EMC compliance, the design should incorporate strategies such as proper PCB stack up, proper grounding,
shielding, and trace routing. These techniques help minimize EMI emissions and susceptibility, ensuring the device operates
effectively in its intended environment.
Application in OrCAD X Presto:
1. Implement ground planes:
a. Go to Setup > Cross Section
b. Ensure dedicated ground planes are included in the stackup for effective return paths
2. Use guard traces:
a. Use Route > Add Dynamic Shape to create guard traces around sensitive signals like DDR3 clocks
b. Connect guard traces to ground at regular intervals using stitching vias
3. Add stitching vias:
a. Use Place > Via and select a predefined via definition
b. For automatic stitching, use Tools > Add Stitching
c. Set parameters for via spacing (e.g., every 500 mils) to enhance grounding
4. Route high-speed signals on inner layers:
a. Use Route > Interactive Routing and select inner layers for critical high-speed nets
b. This reduces EMI by shielding signals with adjacent ground planes
5. Minimize loop areas:
a. Ensure power and ground traces run parallel to minimize loop areas
b. Use Route > Power Planes to define power distribution areas that overlap with ground planes
6. Stub Length Control
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OrCAD X High-Speed Digital Design Guide
