Applying Decoupling Rules

To change EMI Scanner Decoupling rules:

1. Launch EMI Scanner.

   The EMI Scanner window appears, on the Rules tab.

   

2. From the Rules pane, select one of the seven subcategories under Decoupling:
   • Decoupling Capacitor Density – displays Decoupling Capacitor Density rule configuration.

     

     This rule states that decoupling capacitors must be placed between all adjacent plane pairs within a specified grid density.

     From here, you can set the following:

     • Rule State – toggles Decoupling Capacitor Density rules on or off.
     • Check Only for Pwr-to-Gnd Plane Decoupling – sets whether to ignore plane-to-plane decoupling and check only for decoupling capacitors between power and ground planes.
     • Grid Size (X Direction) – specifies the size of the grid used to check for decoupling capacitors. Used in conjunction with Grid Size (Y Direction).
     • Grid Size (Y Direction) – specifies the size of the grid used to check for decoupling capacitors. Used in conjunction with Grid Size (X Direction).
     • Number of Decoupling Caps Required within Each Grid – specifies the number of decoupling capacitors connecting between planes that are required within each grid location.
     • Number of Vias Required within Each Grid – specifies the number of vias connecting between planes that are required within each grid location. You must select Allow Via Connection for Same Net Name to use this option.
     • Sort by Column – specifies the column by which results are sorted.
     • Log File State – determines whether EMI Scanner creates a log file with additional details (intended for use in debugging).
     • Weighting Factor – specifies the weighting factor (0<factor<=1) that is applied to violations of this rule when assigning a rank. A violation's rank is its own "degree of badness" multiplied by the weighting factor. See Exporting EMI Scanner Results and Analyzing EMI Scanner Results Using iQ-Harmony.
     • Allow Via Connection for Same Net Name – determines whether EMI Scanner allows a via in place of a decoupling capacitor when the two planes are the same net name.
     • Include Power/Ground Islands on Signal Layers – specifies whether to check for decoupling on power/ground islands.
     • Check Only When Grid on Board by at Least – specifies the percentage of a grid that must be on the board in order for it to be checked.
     • Ignore Violations from Pwr/Gnd Nets with Same Name – determines that only one plane of a given name is checked for violations (e.g., if two planes are "gnd" and a violation occurs between gnd and another layer, only one violation is reported).
     • Require One Capacitor Pin to be Inside Grid – changes how EMI Scanner determines whether a component is inside or outside the grid. See Technical Note.
     • Require ALL Capacitor Pins to be Inside Grid – changes how EMI Scanner determines whether a component is inside or outside the grid. See Technical Note.
     • Layer Choice – specifies the layers to include in this rule analysis.
   • Power Pin Capacitor Distance – displays Decoupling Capacitor Distance from IC Power Pin rule configuration.

     

     This rule states that a decoupling capacitor must be connected between the power and ground-reference planes and be placed within a specified distance of each IC power pin.

     From here, you can set the following:

     • Rule State – toggles Power Pin Capacitor Distance rules on or off.
     • Max Distance between Decoupling Cap and IC Power Pin – specifies the maximum distance between an IC power pin and its decoupling capacitor.
     • Sort by Column – specifies the column by which results are sorted.
     • Log File State – determines whether EMI Scanner creates a log file with additional details (intended for use in debugging).
     • Weighting Factor – specifies the weighting factor (0<factor<=1) that is applied to violations of this rule when assigning a rank. A violation's rank is its own "degree of badness" multiplied by the weighting factor. See Exporting EMI Scanner Results and Analyzing EMI Scanner Results Using iQ-Harmony.
     • Maximum Search Distance for Cap – specifies a maximum search distance for a capacitor. A larger search box increases the chances of EMI Scanner finding capacitors, but can slow processing time.
     • Allow Capacitors on Both Sides of Board – specifies whether to include capacitors on both sides of the board.
     • Require Only One Cap Pin to be Within Specified Distance – changes how EMI Scanner determines whether a component is inside or outside the grid. See Technical Note.
     • Require ALL Cap Pins to be within Specified Distance – changes how EMI Scanner determines whether a component is inside or outside the grid. See Technical Note.
     • ICs to Check – selects the types of components to include in this rule analysis.
   • IC Power/Ground Pin-Via Distance – displays IC Power/Ground-Reference Pin Distance to Via rule configuration.

     

     This rule states that the trace connecting the IC power/ground reference pin to its associated via to the power/ground-reference plane must be no longer than a specified distance.

     From here, you can set the following:

     • Rule State – toggles IC Power/Ground Pin-Via Distance rules on or off.
     • Maximum Distance between IC Pin and Via – specifies the maximum distance between the center of the IC power or ground-reference pin and the center of the via to the power or ground-reference plane.
     • Sort by Column – specifies the column by which results are sorted.
     • Log File State – determines whether EMI Scanner creates a log file with additional details (intended for use in debugging).
     • Weighting Factor – specifies the weighting factor (0<factor<=1) that is applied to violations of this rule when assigning a rank. A violation's rank is its own "degree of badness" multiplied by the weighting factor. See Exporting EMI Scanner Results and Analyzing EMI Scanner Results Using iQ-Harmony.
     • Maximum Search Distance for Via – specifies a maximum search distance for a via when a violation is found. This allows you to spot vias that are barely outside the original requirement and therefore not serious violations.
     • Check Power/Ground Pins Without Plane – checks the distance between the IC power/ground pin and its via when the power/ground plane has not been completed yet.
     • Verify Via Connected to Appropriate Plane – selecting 'no' speeds up EMI Scanner by not verifying that the via connects to an appropriate plane (shape).
   • Decoupling Cap Distance to Via – displays Decoupling Capacitor Distance to Via rule configuration.

     

     This rule states that the trace connecting a decoupling capacitor to its associated via to the power/ground-reference plane must be no longer than the specified distance.

     From here, you can set the following:

     • Rule State – toggles Decoupling Cap Distance to Via rules on or off.
     • Maximum Distance Between Capacitor and Via – specifies the maximum distance between the capacitor pin and the center of the via to the power or ground-reference plane.
     • Sort by Column – specifies the column by which results are sorted.
     • Log File State – determines whether EMI Scanner creates a log file with additional details (intended for use in debugging).
     • Weighting Factor – specifies the weighting factor (0<factor<=1) that is applied to violations of this rule when assigning a rank. A violation's rank is its own "degree of badness" multiplied by the weighting factor. See Exporting EMI Scanner Results and Analyzing EMI Scanner Results Using iQ-Harmony.
     • Maximum Search Distance for Via – specifies a maximum search distance for a via when a violation is found. This allows you to spot vias that are barely outside the original requirement and therefore not serious violations.
     • Verify Via Connected to Appropriate Plane – selecting 'no' speeds up EMI Scanner by not verifying that the via connects to an appropriate plane (shape).
   • Power/Ground Trace Decoupling – displays Power/Ground-Reference Trace Decoupling rule configuration.

     

     This rule states that all power and ground-reference traces longer than a specified length must have a decoupling capacitor within a specified distance of the IC power pin.

     From here, you can set the following:

     • Rule State – toggles Power/Ground Trace Decoupling rules on or off.
     • Maximum Ignorable Power/Ground Trace Length – specifies the maximum power/ground trace length that may be ignored. All traces longer than this length must meet this rule's requirement.
     • Max Distance between Cap and IC Power Pin – specifies the maximum distance between the capacitor pin and the power or ground-reference pin.
     • Sort by Column – specifies the column by which results are sorted.
     • Log File State – determines whether EMI Scanner creates a log file with additional details (intended for use in debugging).
     • Weighting Factor – specifies the weighting factor (0<factor<=1) that is applied to violations of this rule when assigning a rank. A violation's rank is its own "degree of badness" multiplied by the weighting factor. See Exporting EMI Scanner Results and Analyzing EMI Scanner Results Using iQ-Harmony.
     • Net Choice – specifies the nets to include in this rule analysis. Select one, or Ctrl+click to select multiple nets.
   • Power/Via Density – displays Power Via Density rule configuration.

     

     This rule checks for power planes that do not have enough adjacent layer via connections.

     From here, you can set the following:

     • Rule State – toggles Power Via Density rules on or off.
     • Minimum Number of Vias – sets the minimum number of vias required to connect adjacent power planes.
     • Use Grid – toggles the use of a grid on or off.
     • Grid Size (X Direction/Y Direction) – when Use Grid is enabled, these fields specify the size of the grid.
     • Number of Vias Required within Each Grid – when Use Grid is enabled, specifies the number of vias required within each grid.
     • Check Only When Grid on Board by at Least – specifies the percentage of the grid that must be on the board for analysis to occur.
     • Sort by Column – specifies the column by which results are sorted.
     • Log File State – determines whether EMI Scanner creates a log file with additional details (intended for use in debugging).
     • Weighting Factor – specifies the weighting factor (0<factor<=1) that is applied to violations of this rule when assigning a rank. A violation's rank is its own "degree of badness" multiplied by the weighting factor. See Exporting EMI Scanner Results and Analyzing EMI Scanner Results Using iQ-Harmony.
   • Reference Overlap – displays Disparate Reference Overlap rule configuration.

     

     The Disparate Reference Overlap rule checks for overlapping reference planes from different domains.

     From here, you can set the following:

     • Rule State – toggles Disparate Reference Overlap on or off.
     • Maximum Total Overlap Area – specifies the maximum overlap area that is acceptable. Overlap over this maximum will report a violation.
     • Nets to Include in Reference Group A – selects a net type.
     • Nets to Include in Reference Group B – selects a net type.
     • Sort by Column – specifies the column by which results are sorted.
     • Log File State – determines whether EMI Scanner creates a log file with additional details (intended for use in debugging).
     • Weighting Factor – specifies the weighting factor (0<factor<=1) that is applied to violations of this rule when assigning a rank. A violation's rank is its own "degree of badness" multiplied by the weighting factor. See Exporting EMI Scanner Results and Analyzing EMI Scanner Results Using iQ-Harmony.
3. Rules are automatically saved for the current EMI scan. To save them for a future scan, click Save Rules.