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Calculate Differential and Coplanar Differential Transmission Lines

This calculation type allows you to calculate the differential characteristic impedance and secondary parameters of a differential pair or coplanar differential pair with specified geometric and electrophysical parameters.

Example

Walkthrough

To perform a calculation of differential transmission lines in lossless mode, follow these steps:

  1. Set the calculation settings as shown below:

    • Set Target to Transmission line
    • Set Target type to Diff pair or Coplanar diff pair
    • Set Mode to Lossless

    Initial calculation settings

  2. Select the required transmission line model and review it in the preview area.

    Select and preview model

  3. Define the input parameters for the selected transmission line.

    For a differential pair, the parameter set includes:

    • H – Dielectric thickness. For each dielectric layer, you can specify its own thickness using the H1..H4 parameters (the number of H(n) parameters is determined by the number of dielectric layers).
    • Er – Dielectric constant. For each dielectric layer, you can specify its own dielectric constant using the Er1..Er4 parameters (the number of Er(n) parameters is determined by the number of dielectric layers).
    • W1 – Trace width.
    • W2 – Trace width after undercut.
    • S1 – Diff-pair trace spacing.
    • T1 – Trace thickness.
    • C1 – Coating thickness.
    • CEr – Coating dielectric constant.

    Differential pair parameters

    For a coplanar differential pair, the parameter set also includes:

    • D1 – Distance from the trace to the reference plane.

    Coplanar differential pair parameters

  4. Ensure Impedance is selected as the calculated parameter.

    Impedance selected as calculated parameter

  5. Click Calculate in the lower-right corner of the calculation tab to run the calculation.

    Calculate button

    Before running the calculation, you can click the dropdown arrow next to the Calculate button to choose between two calculation saving options:

    Calculate dropdown options

    • Overwrite calculation – Saves the modified input parameters to the current calculation, overwriting previous data.
    • Save as new calculation – Saves the modified input parameters to a new calculation. This calculation will appear in the Projects panel.

Calculation Results

The calculated parameters of the transmission line are shown in the results table at the bottom of the tab.

Differential pair calculation results

  • Zdiff / Zcomm / Zodd / Zeven – Characteristic impedance (Ohm)
  • Tpd – Propagation delay (ps/m)
  • C – Capacitance per unit length (pF/m)
  • Vp – Signal propagation velocity (m/s)
  • L – Inductance per unit length (nH/m)
  • EEr – Effective dielectric constant

You can configure the result display settings in the Calculation results panel.

Result display mode

  • Differential – Displays the differential characteristic impedance (Zdiff) in the results table.
  • Common – Displays the characteristic impedance in common mode (Zcomm) in the results table.
  • Odd – Displays the characteristic impedance in odd mode (Zodd) in the results table.
  • Even – Displays the characteristic impedance in even mode (Zeven) in the results table.

See Also