Signal Integrity TUTORIAL

Differential Impedance Calculator - Stripline

Following is the formula for differential impedance for a Stripline.

Z diff = 2* Zo (1 - 0.347 e-2.9D/B)

Zo = Single Ended impedance
D = Separation between the differential traces
B = separation between reference planes

As seen from the formula when D decreases, while keeping B constant, Zdiff decrease. It actually depends upon the D/B ratio.

Calculatiing the differential impedance is a two two step process. First Calculate the single ended impedance Zo. In the next step you calculate the differential impedance.

Zo is in Ohms. The Units of B and D does not matter as long as both are same. They should be both in mils or both in meters, for example. After entering values, click on Zdiff button.

Zo Characteristic Impedance :
D edge to edge spacing
B plane to plane separation
  (Differential Impedance) :

In the next page we will learn about decoupling capacitors.