Controlled Impedance Formulas

You must use planes in your design if you wish to use Controlled Impedance Routing Features in Altium.

The downside to using planes in Altium is that you can not route traces that belong to nets within the plane.

Traces on planes are used to create:

Plane to Plane Clearances or Slots in the Plane.
Pull Back Copper from the Board Outline.
Create Split Planes and Nested Planes.

The upside is you get to use automatically controlled impedance line widths.

Equations for Microstrip (Simple trace on Plane):

CharacteristicImpedance = (60/SQRT(Er*(1-EXP(-1.55*(0.00002+TraceToPlaneDistance)/TraceToPlaneDistance))))*LN(5.98*TraceToPlaneDistance/(0.8*TraceWidth+TraceHeight)) TraceWidth = ((5.98*TraceToPlaneDistance)/EXP(CharacteristicImpedance/(60/SQRT(Er*(1-EXP(-1.55*(0.00002+TraceToPlaneDistance)/TraceToPlaneDistance)))))-TraceHeight)/0.8

Equations for Stripline (Simple trace asymmetrically placed between two planes):

CharacteristicImpedance = (80/SQRT(Er))*LN((1.9*(2*TraceToPlaneDistance+TraceHeight)/(0.8*TraceWidth+TraceHeight)))*(1-(TraceToPlaneDistance/(4*(PlaneToPlaneDistance-TraceHeight-TraceToPlaneDistance)))) TraceWidth = ((1.9*(2*TraceToPlaneDistance+TraceHeight))/(EXP((CharacteristicImpedance/(80/SQRT(Er)))/(1-(TraceToPlaneDistance/(4*(PlaneToPlaneDistance-TraceHeight-TraceToPlaneDistance))))))-TraceHeight)/0.8