The following procedures describe how to configure the routing design rules for differential pairs. This is done in the Rule Editor dialog: Differential Pairs tab. Launch this dialog as follows:
- In eCADSTAR Library Editor,
click Home > Editors >
Rule. - In eCADSTAR PCB Editor,
click Home > Design Rules > Rule Editor. Alternatively,
click Design > Design Rules > Rule
Editor.
Setting the Default Differential Pair Rule Stack
Set the differential pair rule stack that is referenced, by default, for differential pair routing, as follows.
- In the Differential pair rule stack box, enter a new differential pair rule stack name and click Add.
- In the Default differential pair rule stack for board box, select the differential pair rule stack that you added in the Differential pair rule stack box.
Configuring the Differential Pair Rule Stack
For each conductor layer, set the design rules for differential pair routing in the Differential pair rule stack table.
Calculating Differential Impedance
- For each layer, enter a value for Track width in the Differential pair rule stack table and press Return.
- For each layer, enter a value for Track spacing in the Differential pair rule stack table and press Return.
- Click Calculate differential impedance. Values for differential impedance and delay are calculated, based on the values that you specify, and displayed in the Differential pair rule stack table.
Calculating Track Width
- Create a new Differential pair rule stack by defining its name and clicking Add in the Differential pair rule stack section.
- Click Calculate differential impedance -> Track Width. The Calculate Differential Impedance -> Track Width dialog is displayed.
- In the Differential impedance -> Track Width dialog, Calculation mode, select Track width.
- For each layer, enter a value for Target differential impedance [Ω] and press Return.
- For each layer, enter a value for Track spacing and press Return.
- Click Calculate Track Width. Values for Track Width, Differential impedance calculated value [Ω], and Delay are calculated, and displayed in the Calculate Differential Impedance -> Track Width dialog.
- Click Apply calculated results to diff. pair rule stack. The calculated values are displayed in the Differential pair rule stack table.
Note
- Multiple rule stacks can be created simultaneously by entering multiple names, separated by a space.
- Delay is displayed in either nanoseconds or picoseconds, depending on the value specified in the Delay section, in the Application Settings dialog, Interaction tab. You must restart Rule Editor to apply changes to this setting.
Calculating Track Spacing
- Create a new Differential pair rule stack by defining its name and clicking Add in the Differential pair rule stack section.
- Click Calculate differential impedance -> Track Width. The Calculate differential impedance -> Track Width dialog is displayed.
- In the Differential impedance -> Track Width dialog, Calculation mode, select Track spacing.
- For each layer, enter a value for Target differential impedance [Ω] and press Return.
- For each layer, enter a value for Track width and press Return.
- Click Calculate Track Spacing. Values for Track spacing, Differential impedance calculated value [Ω] and Delay are calculated and displayed in the Calculate Differential Impedance -> Track Width dialog.
- Click Apply calculated results to diff. pair rule stack. The calculated values are displayed in the Differential pair rule stack table.
Note
- To correctly calculate track widths and spacings, impedances and delays, accurate values for layer thickness, resistivity, dielectric constant and loss tangent must be provided in the layer configuration.
- Multiple attempts may be needed to produce the required value for differential impedance.
