Differential impedance of an edge coupled stripline

Relative permitivity ϵ_r

Dielectric height h μm

Conductor thickness t μm

Conductor width w μm

Separation s μm

Differential impedance Z_diff ≈ Ω

Valid for 0.1 ≤ w / h ≤ 2.0 and t / h ≤ 0.25.

Formulas used

$Z_d &=& 2 Z_0 \left(1 - 0.347 e^{\left(\displaystyle\frac{-2.9 \, s}{2 h + t }\right)}\right)\\ Z_0 &=& \frac{120}{ \sqrt{\varepsilon_r}} \ln\left({1.9 \frac{2 h + t }{0.8 w + t}}\right)$

Valid for 0.1 ≤ w / h ≤ 2.0 and t / h ≤ 0.25

where,
	Z_o	: single ended impedance
	Z_d	: differential impedance
	e_r	: relative permitivity
	h	: height of the dielectric [μm]
	s	: side gap between the conductors [μm]
	t	: thickness of the conductor [μm]
	w	: width of the conductor [μm]

REFERENCE

Brian C. Wadell, "Transmission line design handbook", Artech House, Boston, May 31 1991, ISBN 0-89006-436-9
Howard Johnson, Martin Graham, "High Speed Digital Design: A Handbook of Black Magic", Prentice hall, April 18 1993, ISBN 0-13-395724-1

Relative permitivity ϵ_r
Dielectric height h	μm
Conductor thickness t	μm
Conductor width w	μm
Separation s	μm
Differential impedance Z_diff ≈	Ω
Valid for 0.1 ≤ w / h ≤ 2.0 and t / h ≤ 0.25.