Altium Designer Documentation

Impedance Formula Editor

Modified by Susan Riege on Feb 22, 2018

The Impedance Formula Editor dialog

Summary

This dialog allows you to view and (if required) modifythe formulae used to calculate Impedance and Trace Width when using impedance-controlled routing.

Access

The dialog is accessed from the PCB Editor by clicking the Impedance Calculation button in the Layer Stack Manager dialog. The latter is accessed by choosing Design » Layer Stack Manager from the main menus.

Options/Controls

Microstrip Tab

Click this tab to access formulae used when a route has a plane layer present on only one side of it (referred to as a microstrip).

  • Calculated Impedance - this region of the tab presents the current formula used in the calculation of the routing impedance. The formula can be modified as required, either directly in-situ or through use of the Query Helper, accessed by clicking the Helper button. The default formula is:

(60/SQRT(Er*(1-EXP(-1.55*(0.00002+TraceToPlaneDistance)/TraceToPlaneDistance))))*LN(5.98*TraceToPlaneDistance/(0.8*TraceWidth+TraceHeight))

  • Calculated Trace Width - this region of the tab presents the current formula used in the calculation of the routing trace width, which is used in the impedance formula. The formula can be modified as required, either directly in-situ, or through use of the Query Helper, accessed by clicking the Helper button. The default formula is:

((5.98*TraceToPlaneDistance)/EXP(CharacteristicImpedance/(60/SQRT(Er*(1-EXP(-1.55*(0.00002+TraceToPlaneDistance)/TraceToPlaneDistance)))))-TraceHeight)/0.8

The following pair of buttons are available for each formula region:

  • Helper - click to access the Query Helper dialog with the current formula loaded ready to make changes as required. While you can modify the formula directly in its region, especially if you are proficient with the Query Language, the Query Helper provides additional support with function keywords, operators and a syntax checker.
  • Default - click to load the region with the default formula.
Note that if the plane layer is not adjacent to the signal layer then the nearest plane layer will be used in the calculations.

Stripline Tab

Click this tab to access formulae used when a route has planes present on both sides of it (referred to as a stripline).

  • Calculated Impedance - this region of the tab presents the current formula used in the calculation of the routing impedance. The formula can be modified as required, either directly in-situ, or through use of the Query Helper, accessed by clicking the Helper button. The default formula is:

(80/SQRT(Er))*LN((1.9*(2*TraceToPlaneDistance+TraceHeight)/(0.8*TraceWidth+TraceHeight)))*(1-(TraceToPlaneDistance/(4*(PlaneToPlaneDistance-TraceHeight-TraceToPlaneDistance))))

  • Calculated Trace Width - this region of the tab presents the current formula used in the calculation of the routing trace width, which is used in the impedance formula. The formula can be modified as required, either directly in-situ, or through use of the Query Helper, accessed by clicking the Helper button. The default formula is:

((1.9*(2*TraceToPlaneDistance+TraceHeight))/(EXP((CharacteristicImpedance/(80/SQRT(Er)))/(1-(TraceToPlaneDistance/(4*(PlaneToPlaneDistance-TraceHeight-TraceToPlaneDistance))))))-TraceHeight)/0.8

The following pair of buttons are available for each formula region:

  • Helper - click to access the Query Helper dialog, with the current formula loaded, ready to make changes as required. While you can modify the formula directly in its region, especially if you are proficient with the Query Language, the Query Helper provides additional support with function keywords, operators and a syntax checker.
  • Default - click to load the region with the default formula.
Note that if the plane layers are not adjacent to the signal layer then the nearest plane layers will be used in the calculations. Note also that an offset stripline configuration is not supported.

 

Found an issue with this document? Highlight the area, then use Ctrl+Enter to report it.

Contact Us

Contact our corporate or local offices directly.

You are reporting an issue with the following selected text
and/or image within the active document:
ALTIUM DESIGNER FREE TRIAL
Altium Designer Free Trial
Let’s get started. First off, are you or your organization already using Altium Designer?

If would like to speak with a representative, please contact your local Altium office.
Copyright © 2019 Altium Limited

In that case, why do you need an evaluation license?

If would like to speak with a representative, please contact your local Altium office.
Copyright © 2019 Altium Limited

Got it. You actually don’t need an evaluation license for that.

Click the button below to download the latest Altium Designer installer.

Download Altium Designer Installer

If would like to speak with a representative, please contact your local Altium office.
Copyright © 2019 Altium Limited

Please fill out the form below to get a quote for a new seat of Altium Designer.

By clicking “Get Your Free Trial”, you are agreeing to our Privacy Policy.
You may receive communications from Altium and can change your notification preferences at any time.

If you are on Altium Subscription, you don’t need an evaluation license.

If you are not an active Altium Subscription member, please fill out the form below to get your free trial.

By clicking “Get Your Free Trial”, you are agreeing to our Privacy Policy.
You may receive communications from Altium and can change your notification preferences at any time.

Why are you looking to evaluate Altium Designer?

If would like to speak with a representative, please contact your local Altium office.
Copyright © 2019 Altium Limited

You came to the right place! Please fill out the form below to get your free trial started.

By clicking “Get Your Free Trial”, you are agreeing to our Privacy Policy.
You may receive communications from Altium and can change your notification preferences at any time.

Sounds exciting! Did you know we offer special discounted student licenses? For more information, click here.

In the meantime, feel free to request a free trial by filling out the form below.

By clicking “Get Your Free Trial”, you are agreeing to our Privacy Policy.
You may receive communications from Altium and can change your notification preferences at any time.

Got it. You can download a free Altium Designer Viewer license which is valid for a 6 months.

Please fill out the form below to request one.

By clicking “Get Your Free Trial”, you are agreeing to our Privacy Policy.
You may receive communications from Altium and can change your notification preferences at any time.

That’s great! Making things is awesome. We have the perfect program for you.

Upverter is a free community-driven platform designed specifically to meet the needs of makers like you.

Click here to give it a try!

If would like to speak with a representative, please contact your local Altium office.
Copyright © 2019 Altium Limited

Got it. You can download a free Altium Designer Viewer license which is valid for a 6 months.

Please fill out the form below to request one.

By clicking “Get Your Free Trial”, you are agreeing to our Privacy Policy.
You may receive communications from Altium and can change your notification preferences at any time.