Chapter 6 PCB Calculators
© National Instruments Corporation 6-11 NI Ultiboard User Manual

Embedded Microstrip Differential Impedance Equations

The equations used to perform the embedded microstrip differential
impedance calculations are:
Z0 = 56*ln(5.98*H/(0.8*W+T))/sqrt(Er*(1-exp(-1.55*H1/H)))
Tpd = 84.66667*sqrt(Er*(1-exp(-1.55*H1/H)))
C0 = Tpd/Z0
L0 = C0*Z0*Z0
Zdiff = 2*Z0*(1-0.48*exp(-0.96*S/H1))
Centered Stripline Calculations
Complete the following steps to perform centered stripline differential
impedance calculations:
1. Select Tools»PCB Differential Impedance Calculator.
2. Select Centered Stripline in the Type drop-down list.
3. In the Input Data area, edit the following fields as desired:
•Input Length Unit—Select mils or millimeters.
•Dielectric Thickness (H)—Refer to the figure below.
•Trace Thickness (T)—Refer to the figure below.
•Trace Width (W)—Refer to the figure below.
•Trace Spacing (S)—Refer to the figure below.
•Relative Permittivity (epsilon r)—Refer to the figure below.
Or
If you wish to define the Characteristic Impedance (Zo) yourself, click
User Defined Zo and edit the following fields as desired:
•Input Length Unit—Select mils or millimeters.
•Dielectric Thickness (H)—Refer to the figure below.
•Trace Spacing (S)—Refer to the figure below.
•Characteristic Impedance (Zo)—Refer to the figure below.