This calculator determines the differential impedance of a microstrip line from its physical dimensions and the properties of the substrate. It is essential for high-frequency PCB design, where the balance between differential traces directly influences signal quality.
Formulas
Z0 = (87 / √(εr + 1.41)) × ln((5.98 × h) / (0.8 × w + t))
Zd = (174 / √(εr + 1.41)) × ln((5.98 × h) / (0.8 × w + t)) × (1 − 0.48 × exp(−0.96 × (d/h)))
Explanation of formulas
Z0 represents the characteristic impedance of a single microstrip track, while Zd is the differential impedance of the pair of tracks. Parameters include the width of the track (w), the distance between the two tracks (d), the thickness of the copper (t), the height of the substrate (h), and the dielectric constant of the material (εr). These values influence the propagation speed and the quality of the differential signal.
Uses of the calculator
- Differential pair design for USB, HDMI, Ethernet and other high-speed buses.
- Optimization of signals in RF and microwave circuits.
- Quick assessment of the effect of dimensions on impedance.
- Reference tool for PCB design engineers.