This calculator determines the differential impedance of a pair of coupled microstrips, from the simple impedance Z0, the separation between the tracks and the thickness of the dielectric. It is essential for the design of high-speed differential lines to ensure balanced and interference-free transmission.
Useful for electronic engineers, circuit board designers and students working on differential connections in high frequency communications systems.
Formula
Zd = 2 × Z0 × ( 1 – 0.48 × exp( -0.96 × (d/h) ) )
Explanation of the formula
- Z0 is the simple impedance of a single track (in ohms).
- d is the distance between the two tracks (in mils).
- h is the thickness of the dielectric substrate (in mils).
- The exponential term adjusts for the reduction in impedance due to the electromagnetic coupling between the two traces.
100 ohm differential microstrip impedance
Input : Z0 = 55 Ω, d = 12 mils, h = 6 mils
Output : Zd ≈ 100.2 Ω
Benefits and uses
- Quickly calculates differential impedance for coupled microstrip lines.
- Optimizes the design of high-speed circuits and differential signals.
- Useful for designing differential pairs like USB, HDMI or Ethernet.
- Improves electromagnetic compatibility and reduces common mode noise.