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Design Notes

Current Density Back Annotation of Circuit Routing

This project shows the ability of the AWR design tool to automatically back annotate your circuit layout with accurate current density using Inets (Intelligent nets).  In addition, the tool will color code the annotation depending upon the margin of pass/failure of the design rules.  The circuit example is kept extremely simple to focus attention on the interconnect routing between circuit elements. 


There a 2 separate schematic/layout examples:

1.   Simple Interconnect:

This schematic demonstrates the pass/failure of 5 separate current branches.  There are 2 resistors (3 kohm + 3 kohm) in each branch connected to a 3 V supply.  Each branch is identical with 0.5 mA current flow.  The difference is shown in the layout with varying widths of interconnect to demonstrate varying degrees of pass/failure of the current density design rule.  Choose Simulate > Analyze.  After the circuit/layout has been analyzed, the current densities are back annotated on the layout with color coding to represent various degrees of pass/fail.  Notice the dark colors (blue and purple) represent pass conditions while bright colors (red, orange, yellow) represent failure conditions.

View the dialog box for the current density measurement by double-clicking the INET_J annotation under Simple Interconnect schematic in the Project tab.  The “Symbol size (m)” field defines the size of the text denoting current density on the schematic.  The “Specify max density (A/m^2)” defines the design rule for current density color coding pass/failure.

2.   Multiple Segment Interconnect:

This schematic shows only a single branch of 0.5 mA.  However, the layout shows a path of multiple segments of varying width, varying metal layers, and varying number of vias between metal layers.  As in the 1st schematic, after the circuit is analyzed, the layout is back annotated with varying degrees of color coded current density.

Zoom to any group of vias in the multi-segment line.  Double-click the vias.  The vias will be highlighted with a blue border and diamonds in each corner.  Drag the cursor over one of the blue diamonds until the cursor turns to cross-hairs, then click and drag to re-size the vias.  Notice the current density associated with the vias is automatically updated.

Double-click the multi-segment line in the layout.  Right mouse click and choose Shape Properties, then choose Segments tab.  All 5 segments of our line are listed.  Select any segment under the Line column to obtain a drop down list of all metal layers.  Try selecting any other metal layer and notice the layout and current density are updated automatically.

Schematic - Multiple_Segement_Interconnect

Schematic - Simple_Interconnect

Schematic Layout - Multiple_Segement_Interconnect

Schematic Layout - Simple_Interconnect