EMI Bites: Why Controlled Impedance Traces Matter
If your signal integrity matters, then controlled impedance is not optional; it’s essential.
Designing traces with controlled impedance means keeping the impedance between the signal trace and the return/reference plane (RRP) constant along the entire length of the trace.
Why this matters:
- Impedance mismatches create signal reflections and distortion.
- Varying trace width or geometry breaks the transmission line’s consistency.
- Poor impedance control leads to signal integrity issues and potential EMI issues.
- Fast digital signals behave like RF; they demand clean, matched paths.
Key Insight:
Controlled impedance starts with a correct stackup and ends with a correct transmission line geometry.
How to design for controlled impedance:
- Keep the trace width constant across the entire route.
- Use impedance calculators to account for trace geometry and its position relative to the RRP.
- Always work with your PCB manufacturer; ask them for the correct trace width based on your stackup and materials used.
- Once you have the recommended width, stick to it to meet your impedance requirement.
—Dario
P.S. Want more EMI control strategies to pass EMC?