The edge coupled differential microstrip transmission line is a common technique for routing differential traces. There are four types of impedance used in characterizing differential trace impedances. This calculator finds both odd and even transmission line impedance. Modeling approximation can be used to understand the impedance of the differential microstrip transmission line.
Inputs
Trace Thickness
T
Substrate Height
H1
Trace Width
W
Trace Spacing
S
Substrate Dielectric
Er
Outputs
Odd (Z):
Even (Z):
Common (Z):
Differential (Z):
Introduction
The edge couple differential microstrip transmission line is a common technique for routing differential
traces. There are four different types of impedance used in characterizing differential trace impedances.
This calculator finds both odd and even transmission line impedance. Modeling approximation can be used to
understand the impedance of the differential microstrip transmission line.
Description
An edge couple differential microstrip transmission line is constructed with two traces referenced to the
same reference plane. There is a dielectric material between them. There is also some coupling between the
lines. This coupling is one of the features of differential traces. Usually it is good practice to match
differential trace length and to keep the distances between the traces consistent. Also avoid placing vias
and other structures between these traces.
Differential Impedance Definitions
Differential Impedance The impedance measured between the two lines when they are driven with
opposite polarity signals. Zdiff is equal to twice the value of Zodd
Odd Impedance The impedance measured when testing only one of the differential traces referenced to
the ground plane. The differential signals need to be driven with opposite polarity signals. Zodd is equal
to half of the value of Zdiff
Common Impedance The impedance measured between the two lines when they are driven with the same
signal. Zcommon is half the value of Zeven
Even Impedance The impedance measured when testing only one of the differential traces referenced to
the ground plane. The differential signals need to be driven with the same identical signal. Zeven is twice
the value of Zcommon
Microstrip Transmission Line Models
Models have been created to approximate the characteristics of the microstrip transmission line.
