Applies to
Layout Editor

Purpose
In Signal transmission ,if all the energy is not absorbed by the load then the left over energy can interact with the original signal (depending on the polarity of the energy), and implies degradation of signal quality, jitter etc. Effective coupling between source and load can be achieved by impedance matching. In EDWinXP the impedance can be controlled in the layout editing phase by routing the traces at defined impedance. Optimal trace widths calculated with help of impedance calculator for every layer in the stack, may be stored as design rules.

Operation
Invoke Characteristic Impedance calculator from Tools.

Stack Design

Select Stack Layers

Displays the stack layers used in the PCB from Top to bottom.
 
Make New Stack

Select the required stack layers and click on Make New Stack button. Click Yes on stack design window. Stack layers created will be displayed as shown in the above figure. There is also provision to choose the stack layer types and set the dielectric material properties.

Insert Selected Layers in the stack

Select the stack layer which is to be inserted and click on the Insert Selected Layers in the stack button. The selected stack layer will get inserted to the current stack.

Make Stack of currently used Layers

Click on Make Stack of currently used Layers button to create stack of currently used layers.


Dielectric material property

Dielectric material properties are displayed in this field. Properties can be set depending upon the dielectric used on the PCB. Provisions for selecting dielectric materials from the library and saving the dielectric to the library are also provided.

Select material from library

Displays Dielectric material library. Double click on the dielectric material to select that material. You can also remove the materials from the Dielectric library .
Store properties in library
After setting the properties of dielectric material click on Store properties in library button to Store that material in the library.

Calculations

The program calculates characteristic impedance, Trace Width, Cu Thickness, Thickness of dielectric, and Permittivity.
Thickness of dielectric material, permittivity of dielectric material, Cu thickness and trace width on signal layers can be assigned. The program calculates required trace width, Cu thickness, thickness of dielectric, and permittivity for the layer when value of characteristic impedance is specified as a design rule.

Operation
 
For calculation double click on signal or mixed layer. Set values for the variables. Select the variable to calculate from the Calculate variable drop down menu. Program automatically applies suitable characteristic impedance formula depending on layer configuration. (Microstrip, Stripline and Dual Stripline). You can save the out put to an ASCII file.


Dielectric Materials Library

Library of common dielectric materials are integrated with calculator. Entries in this library may be edited and new materials can be added.

Design Rules Settings

Optimal trace widths calculated with help of impedance calculator for every layer in the stack, may be stored as design rules. These rules will apply for all nets that have been assigned status “impedance controlled net”.

Operation

Select the impedance controlled nets form the list of Available Nets. Save the trace width of selected nets as design rules. After setting the design rules whenever a trace for impedance controlled net is routed, the trace width will reset to width set for currently routed layer (assuming that this layer is included in the stack).
 
For example,the optimal trace width calculated for layer B is 1.215mm. This width is automatically assigned to trace segment originating on this layer. After layer change to “K”, trace width switches automatically to .003mm”. Returning to layer 'B' causes automatic change of the trace segment width back to .1.215mm: