This calculator estimates the differential impedance (Zd) of an edge-to-edge microstrip pair from the single-end impedance Z0, the track spacing d and the dielectric thickness h. Enter d and h in mils and Z0 in ohms to get Zd in ohms, useful during RF PCB design and differential signal integrity validation.
Formula
Zd = 2 × Z0 × ( 1 − 0.48 × exp( −0.96 × (d / h) ) )
Explanation of the formula
The formula adjusts the simple impedance Z0 to take into account the coupling between two tracks separated by d on a substrate of thickness h. The exponential term models the decay of coupling as spacing increases, and the constant 0.48 sets the magnitude of this correction for typical edge-to-edge microstrips.
Uses
- Design and simulation of differential traces on RF PCB.
- Impedance verification for high-speed buses and interfaces.
- Spacing sizing and matching control for 100 Ω or other differential targets.
- Validation tool during routing and prototype development.