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What's Good About PCB SI Static IR Drop Analysis? 16.5 Has Many New Enhancements!

Comments(5)Filed under: SPB, PDN, IBIS-AMI, Allegro, Power, SigXP UI, PCB SI, IBIS, SI analysis and modeling, design, "PCB SI", "PCB PI", IR drop, PCB PI, High Speed, 3D viewer, power integrity, PI, SPB16.5, Allegro 16.5, Allegro PCB SI, 16.5, Grzenia

In the Allegro PCB SI 16.5 release, static IR drop analysis has been integrated into PDN (power delivery network) analysis, with several new features added, such as current density display and the display of current direction.

Read on for more details …

Analyze Menu

To invoke Static IR Drop analyze, select Analyze > Static IRDrop Analysis at the bottom of the PDN Analysis form:


This will open the following window:


Field Solver Preferences

If you select the Preferences button and select the Field Solver tab, you can see the field solver options in the bottom section:

In this tab, you can select to use the full wave model (for high frequencies) or equivalent circuit (for low frequencies) since this option does not affect static IR drop analysis (Static IR drop will calculate the resistor with equations based on the mesh). You can ignore some layers which will ignore all shapes of the specified layers during the modeling. The ambient temperature will be used for static IR drop analysis and PI analysis, the surface roughness is used for PI analysis, and the debye model can be used for future model extraction.

Saving Analysis Results

By default, the analysis results will be saved using the .brd file name with different extensions. If you want to run multiple simulations for the same board file with different settings, you can change the session name for each simulation to store the results. Otherwise, the previous results will be overwritten by the new analysis. Select the Session button in the Static IRDrop Analysis dialog. This will open the Session Name dialog:


Display Options

The Options pane in Allegro PCB SI contains information specific to IRDrop analysis:


The default layer to Review is Top. This layer may or may not have any shapes on it for the DC Nets that are being analyzed. Use the Review pulldown in the Options pane to select a specific layer in the design:


The color contour that appears depends on several factors: the actual analysis results, the threshold values set in the main dialog, and the Color Legend.
Selecting a point on a net that was analyzed will display the value at that location in the Options pane:


To see the display options for static IR drop, right click in the PCB SI canvas to see the menu:

The Set reference command allows you to pick a reference point in the design which will be graphically displayed on the canvas. Subsequent probe points will be displayed in the Options pane with the actual drop value at that point and the relative voltage value to the Reference point. In the Options pane, select the Color Legend radio button, and you will see the following:


In previous releases, this legend was fixed. To change the color legend, select the Custom button in the Options pane to open the Color Legend dialog:


You can set different color legends for different result (current, voltage, impedance, density, and temperature rise) by selecting the Format pulldown and the Method options. Use the RMB menu to select the other Display options for IRDrop analysis - Display Mesh, Display Current, Display Density, and Display TempRise. If you are just running IR Drop, it is not necessary to run the Mesh analysis separately. The mesh that was generated for IR Drop can be accessed using RMB > Display Mesh. If you RMB select 3D EMViewer, the 3D result will be displayed in the 3D EMViewer:


Please share your experiences with this new 16.5 capability.

Jerry "GenPart" Grzenia


By steve on August 12, 2013
I am trying to use the Static IR analysis on a mobile PC board. One of the problems that I am encountering is the Error -- meshing overlapped founded for shapes on layer 0 at xx,yy.
I have set the mesh dimensions to 4mils which is smaller than the gap where the mesh overlap occurs.

By Jerry GenPart on August 13, 2013
Hi Steve,
Please look at page 63 in the documentation located at -
Jerry G.

By sms050 on August 14, 2013
Thanks Jerry. The problem I see is a mesh overlap where a shape (VDD) wraps around a GND via also within a shape. I reduced the pad size on the TOP layer that has the overlap from 20mils to 15mils. After that change the mesh will run on the TOP layer without a overlap error. Is there a way to invert the colors? I assigned each power pin in my bga to a source and made the VRM output a sink so I could see the pin current. I would like a large negative current to be red rather than blue. The color legend custom dialog will not let me make red -5A for example.

By Jerry GenPart on August 15, 2013
Hi "sms050",
I checked with one of our PCB SI Customer Support experts and they state -
"Currently we cannot assign the red color to a negative value"
Jerry G.

By sms050 on August 16, 2013
Hi Jerry

I found that I can re-assign colors in the Color Dialog, but it does not change the legend.

Steve S.

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