Calculating Track Width Stack Values from a Target Characteristic Impedance Value

For a track width stack that you select in the Calculate Characteristic Impedance - > Track Width dialog, this topic explains how to calculate the track width, characteristic impedance and delay per unit length. These values are calculated, based on the target characteristic impedance that you specify.

  1. In eCADSTAR PCB Editor, launch the Rule Editor dialog by clicking Home > Design Rules > Rule Editor. Alternatively, click Design > Design Rules > Rule Editor.
  2. In the Rule Editor dialog, select the Tracks tab.
  3. In the Tracks tab, Track width stack section, select the track width stack for which to calculate the track width, characteristic impedance and delay per unit length.
  4. Click Calculate characteristic impedance -> Track Width. The Calculate characteristic impedance -> Track Width dialog is displayed.
  5. In the Rounding precision for track width box, set the value by which the track width is incremented in order to reach the specified Target characteristic impedance value. When you click Calculate Track Width, the Track width value is automatically incremented by this value until the characteristic impedance is as close as possible to the Target characteristic impedance value. The most accurate results are produced by specifying smaller values.

 

Note
  • When you click Calculate Track Width, the calculated track width is displayed using the number of decimal places specified on the Status Bar. For example:
  • Specifying a rounding precision of 0.01, with 5 decimal places set, produces a track width in the following format: 0.43000.
  • Specifying a rounding precision of 0.01, with 3 decimal places set, produces a track width in the following format: 0.430.
  • If you change the units in the design, then the precision of the calculated track width value may appear to be different as the value is displayed using the new units. However, the specified precision is maintained. For example, in units of mm, specifying a rounding precision of 0.01 might produce a track width of 0.43000. If this value is saved and then the units are changed to inch, the saved value is changed to 0.01693 in the Tracks tab.
  • If the units are set to mil in eCADSTAR, and a value of 0.04 or less is entered in the Rounding Precision for Track Width box, then the calculated track width is displayed with higher precision than specified.

 

  1. In the Calculate characteristic impedance -> Track Width dialog, Track width table, enter a value in the Target characteristic impedance [Ω] box for a particular conductor layer, and press Return. This is the required characteristic impedance for this layer in the relevant track width stack.
  2. Click Calculate Track Width. eCADSTAR attempts to calculate a track width using the Target characteristic impedance [Ω] and Rounding precision for track width values that you specify.
  3. If a track width value is calculated that is between the Minimum and Maximum values for Track Width that are set in the Tracks tab, Track width stack table, then the following columns are updated in the Calculate characteristic impedance -> Track Widthdialog: Track width, Characteristic impedance calculated value [Ω] and Delay. Values are shown in black to indicate that they are acceptable.
  4. If a track width value is calculated that is outside of the Minimum and Maximum values, then the Track width value is shown in red.
  5. If a track width value cannot be calculated using the specified Target characteristic impedance [Ω] and Rounding precision for track width values, then an error message is displayed and is displayed in the Track width, Characteristic impedance calculated value [Ω] and Delay columns.
  1. To execute the track width calculation again, enter new values in the Target characteristic impedance [Ω] and Rounding precision for track width boxes and click Calculate Track Width.
  2. When you are satisfied with the results, click Apply calculated results to track width stack to add the calculated values to the Rule Editor dialog, Tracks tab. The following columns are updated in the Track width stack table for the relevant layer in the track width stack: Typical in the Track width section, Characteristic impedance, and Delay.
  3. Click Apply in the Rule Editor dialog to save the settings.

Checking a Track width value after changing the Units value

  1. After following the above procedure to calculate a track width value for a particular conductor layer in a Track width stack, note the Typical value in the Rule Editor dialog, Track width section, and then close the dialog.
  2. On the Status Bar, select a different value for Units.
  3. Launch the Rule Editor dialog.
  4. In the Tracks Tab, Track width stack section, notice that the Typical value in the Track width section is shown using the new units.
  5. Select a Track width stack value and click Calculate characteristic impedance -> Track Width.
  6. In the displayed Calculate characteristic impedance -> Track Width dialog, notice that the Rounding precision for track width value must now be specified using the new units.
  7. Click Close in the Calculate characteristic impedance -> Track Width dialog.
  8. Click Cancel in the Rule Editor dialog.

 

Related Topics
Calculate Characteristic Impedance - > Track Width Dialog
Rule Editor Dialog: Tracks Tab