Chapter 6
PCB Calculators
©
National Instruments Corporation
6-11
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.
