I am trying to calculate the differential impedance of a differential pair in a 4-layer PCB as follows:

  1. Layer: Low speed signal
  2. Layer: Power plane
  3. Layer: Differential pair
  4. Layer: Ground plane

I am currently using Saturn PCB Toolkit, may I know which settings should I consider:

  1. Edge Cpld Ext (Microstrip)
  2. Edge Cpld Int Sym (Edge-Coupled Symmetrical Stripline)
  3. Edge Cpld Int Asym (Edge-Coupled Asymmetrical Stripline)
  4. Edge Cpld Embed
  5. Broad Cpld Shld
  6. Broad Cpld NShld

Thank you.



If your only high speed signals are on layer 3 then you choose stripline. There is no need stated for an asymetric layer space.

Here is a web tool.

enter image description here
https://www.eeweb.com/tools/symmetric-stripline-impedance enter image description here
https://www.eeweb.com/tools/edge-coupled-stripline-impedance https://www.eeweb.com/tools/edge-coupled-microstrip-impedance https://www.eeweb.com/tools/broadside-coupled-stripline-impedance

| improve this answer | |
  • \$\begingroup\$ Hi Tony, thanks for your answer. Before I confirm on the correct answer, I would like to highlight my question that a stripline doesn't has to be between 2 ground planes right? Like my design, it can be between a power plane and a ground plane. Am I right? \$\endgroup\$ – sfcircuit Jan 29 '18 at 5:14
  • \$\begingroup\$ right. decoupling caps are intended to be <0.1 Ohm in the frequency range of strip lines. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 29 '18 at 5:35
  • \$\begingroup\$ alright, thanks. May I know why do you relate it to a decoupling caps? Asking out of curiosity. \$\endgroup\$ – sfcircuit Jan 29 '18 at 6:04
  • \$\begingroup\$ ac short circuit model equiv planes \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 29 '18 at 10:56

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