Conformal Mesh

Tips and App Notes

We recommend reading the chapter "Conformal Mesh" in the Sonnet User’s Guide for a background discussion of conformal mesh before performing this tutorial.

You use the example file, cm_spiral.son, pictured below, for this example. You can obtain a copy of this file from the Sonnet Examples. If you do not know how to obtain a Sonnet example, select Help => Examples from any program menu, then click on the Instructions button.

Note that the spiral was added to the circuit using the palette of standard geometries (Tools => Add Metalization => Round Spiral).

Sonnet uses staircase fill by default. Using staircase fill, the memory requirement for this circuit is approximately 7000 Mbytes using 30,000 subsections. This analysis would be impossible or prohibitively time consuming to run on most computers. In this tutorial, you will use conformal meshing where appropriate to reduce the number of subsections so that the circuit uses around 2,800 subsections and requires 69 Mbytes of memory.

Below is a close-up of the circuit which shows the high number of rectangular subsections needed to subsection the curves of the spiral. Note that the feedline is a Manhattan polygon and therefore uses fewer, larger subsections.

As discussed in the rules list in Chapter 11, ”Conformal Mesh,” in the Sonnet User’s Guide, we want to use conformal meshing on non-manhattan polygons while continuing to use staircase fill on large rectangular polygons. Our spiral consists of three polygons: the three turn spiral inductor and two feed lines. One feed line is on the same level as the spiral and the other, connected to the spiral by a via, is one level down.

No Polygon Overlap

Rule 1:, "Polygon Overlap" in the Sonnet User’s Guide states that there should be no polygon overlap in a circuit which uses conformal mesh. If you zoom in on the boundary between the spiral conductor and the feedline on level 0, you will observe, as shown below, that the two polygons overlap.

Using the Merge Polygon command is an easy way to remove the overlap from your circuit. To do so, perform the following:

1. Click on the small rectangular polygon which overlaps the conductor to select it.
   
   The polygon is highlighted.
   
   

2. Hold down the Control key and click on the spiral conductor to select it.
   
   Holding down the control key allows you to select another object without de-selecting any previously selected items. Both polygons are now highlighted.
   
   

3. Select Edit => Merge Polygons from the project editor main menu.
   
   The two polygons are merged into one polygon and the overlap is removed.
   
   
   
   Invoking Conformal Meshing
   
   You need to apply conformal meshing to the three turn spiral. To invoke conformal meshing, you apply the Conformal fill type to the spiral conductor polygon. To do so, perform the following:

4. Double-click on the spiral inductor polygon to open the Metalization Properties dialog box for the polygon.
   
   The polygon is highlighted and the Metalization Properties dialog box appears on your display.
   
   

5. Select Conformal from the Fill Type drop list.
   
   This applies conformal subsectioning to the spiral polygon. If a Notice appears, click on the OK button to close the message.

6. Click on the OK button to apply the change and close the dialog box.
   
   Note that the appearance of the polygon does not change.
   
   Viewing Conformal Meshing
   
   To see the effect that conformal meshing has on the subsectioning, you must perform an Estimate Memory command on the circuit and view the subsectioning. To do this, perform the following:

7. Select Analysis => Estimate Memory from the project editor main menu.
   
   A status message appears while the circuit is being evaluated. It may take a few minutes to complete the subsectioning depending on the processing speed and memory available on your computer. Once the subsectioning is complete, the Estimated Memory window appears.
   
   The memory requirement is now around 77 Mbytes and the number of subsections is approximately 2900 subsections.

8. Click on the View Subsections button in the Estimated Memory window.
   
   There is a small delay while the Subsection Viewer is being opened. The circuit is shown with the subsectioning highlighted by black outlines as shown below.
   
   
   
    

 The use of conformal meshing for the spiral inductor reduced the number of required subsections from about 70,000 to 2,800 and required memory from 7,000 Mbytes to about 77 Mbytes. This analysis is now a manageable problem. This concludes the conformal meshing application note.