Stripline Differential Impedance Calculator

PCB CUPID - differential cables 2 - PCB

PCB stripline refers to a type of trace/transmission line that is routed in the inner layers of the PCB. Due to this, it is enclosed by a single material, usually the PCB substrate material. This is most commonly noticed on multilayer PCB designs, where the signal trace is equipped with ground planes both above and below it. Due to this arrangement, the high-frequency signal remains inside the PCB leading to fewer emissions and also provides shielding against incoming signals.

This calculator calculates the differential (ex : D+ & D- from USB) impedance between the positive and negative trace of the transmission line. Here the differential impedance is slightly less than twice the impedance of the single ended impedance. The closer the two traces, the smaller is the differential impedance. Now calculating the differential impedance is a two step process. First you need to calculate the single ended impedance Zo (Characteristic Impedance) then input the characteristic impedance, space between traces, and trace height to determine the impedance between two lines driven differentially.

Stripline PCB differential impedance.

Step – 1: Calculate the Characteristic Impedance (more Info)
Substrate Dielectric
Height of Trace
mm
Trace Thickness
mm
Width of the Trace
mm
Step – 2: Calculate the differential Impedance
Characteristic Impedance
Ohm
Space Between Traces
mm
Height of Trace
mm

Formula

\[d = 2 * z * (1 – 0.347 * e^{(-2.9 * (\frac {S}{H}))})\]

where :

  • d = Differential Impedance
  • z = Characteristic Impedance
  • s = Space between traces
  • h = Height of trace

Any questions? Drop them here!