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Crosstalk

In frequency-domain analysis, you can calculate crosstalk (voltage and phase) at specific frequencies at the near and far ends of matched transmission lines, and determine the minimum trace spacing required to ensure an acceptable crosstalk level. These calculations are supported for single-ended transmission lines and differential pairs.

Examples

Crosstalk Calculation Walkthrough

To perform a Crosstalk calculation, follow these steps:

  1. Set the initial calculation settings:

    • Set Target to Transmission line
    • Set Target type to Single-ended or Diff pair
    • Set Mode to Frequency domain
    • Set Parameters to Crosstalk

    Crosstalk calculation settings

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

    Crosstalk calculation - Select model

  3. Define the input parameters for the transmission line.

    Crosstalk input parameters

    Available parameters are listed below. Some of them may not be available for certain transmission line types.

    • H – Dielectric thickness (mm). 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 (mm).
    • W2 – Trace width after undercut (mm).
    • T1 – Trace thickness (mm).
    • C1 – Coating thickness (mm).
    • CEr – Coating dielectric constant.
    • S1 – Diff-pair trace spacing (mm).
    • TR – Rise time (ps).
    • FREQ – Frequency (MHz).

    Parameters specific to Crosstalk calculations:

    • Transmission line count – The number of lines in the model (2 or 3).

    • V1, V3, V5... – The input voltage applied to Port 1, Port 3, Port 5, respectively. The total number of available voltage inputs corresponds directly to the number of transmission lines in the selected model.

      These parameters must be set to fixed values (+1 V, 0 V, or -1 V) using the drop-down menus. At least one port must be configured with a non-zero voltage.

      The actual crosstalk level scales proportionally with the voltage applied to the non-zero port.

    • LTL – Line length (mm).

    • G1 – Trace gap (mm).

  4. 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 for Single-Ended Lines

For single-ended transmission lines, the following parameters are calculated:

  • Zo – Characteristic impedance (Ohm).
  • UNEXT – Near-end voltage (V).
  • ɸNEXT – Near-end phase (°).
  • UFEXT – Far-end voltage (V).
  • ɸFEXT – Far-end phase (°).

Crosstalk results for single-ended lines

Calculation Results for Differential Lines

For differential transmission lines, the following parameters are calculated:

  • Zodd – Characteristic impedance of the line driven in odd mode (Ohm).
  • Voltage and phase at the near and far ends of each line. The number of calculated parameters (UNEXT, ɸNEXT, UFEXT, ɸFEXT) depends on the selected model and the number of transmission lines.

Crosstalk results for differential lines

Crosstalk calculation results for differential lines can be displayed in three modes:

  • Single-ended
  • Odd mode
  • Even mode

To select the required mode, use the View settings → Mode drop-down in the Calculation results panel.

Crosstalk representation modes

Parametric Sweep

Parametric sweeps for Crosstalk calculations follow the same workflow as other sweeps in SimPCB Lite: you must specify a value range and step size for a selected input parameter.

Parametric sweep - Set value range

Calculation Results

You can display the following calculated parameters in the graph:

  • UNEXT/FEXT – Crosstalk voltage on the selected port(s). Use the View settings → Port drop-down menu in the Calculation results panel to select the port(s) to display.

  • ɸNEXT/FEXT – Crosstalk phase on the selected port(s).

To display multiple calculated parameters in the graph simultaneously, select the required ports in the View settings → Port drop-down menu.

Crosstalk parametric sweep

For differential transmission lines, you can also display calculated parameters in one of the following display modes:

  • Single-ended
  • Odd mode
  • Even mode

Use the View settings → Mode drop-down in the Calculation results panel to select the required display mode:

Crosstalk differential parametric sweep - Choose display mode

See Also