Signal integrity

Signal integrity is a key component of high-speed electronics, such as USB, Bluetooth, wi-fi, and RAM, where boards operate in the GHz space. If you work in this area, signal integrity is essential to your design.

When is the best time to analyze signal integrity? After you have laid out the schematic and placed components on the 2D PCB. Now you are ready to begin routing the board and this is when you want to start considering signal integrity. Using this feature during the routing activity helps you to keep within design requirements as you work. You don’t have to wait until the board is completely designed to start getting important feedback. And, any time significant changes are made, you can update the analysis to see their effect.

Work with the analysis results

The table displays a hierarchical view of the path being analyzed and reports the results. The path row displays the aggregated values for segments in the path. Each segment row displays the results for a single segment.

In the canvas, segments are colored according to their impedance value as shown in the color chart on the right.

• Green represents the target value defined by the input parameters.
• Cooler colors, such as blue, denote lower impedance.
• Warmer colors, such as red, denote higher impedance.

In the table:

• Double-click a path or segment to highlight it in the canvas. The view is zoomed to display the path or segment extents. A temporary border overlay surrounds the selected object.

• The canvas overlay tools include:

  • displays the impedance overlay and legend.
  • turns off overlay display.

• The table tools include, from left to right:

  

  • Stop analysis: Stops the analysis.
  • Refresh table: All results are discarded and paths in the table are reanalyzed. Displays if changes have been made to the board.
  • Delete results: Deletes the table contents.
  • Expand table: Shows all results rows for the analyzed path.
  • Collapse table: Hides all results rows for the analyzed path.
  • Export results: Saves the results data as a file so it can be used outside of Fusion.

• The results table provides the following information:

  • Length: the linear measurement of the segment or path in mils.
  • Impedance: for a path, the value is the range from the lowest segment value to the highest segment value. For a segment, the value is for the selected segment alone. Arrows indicate whether the impedance value is higher or lower than the target impedance.
  • Time delay: explains the amount of time the signal takes to travel from one end point to the other. The value is in picoseconds.
  • Resistance: the measure of opposition to current flow in an electrical circuit. The value is represented in ohms (Ω).
  • Capacitance: describes the ability of a circuit or component to collect and store energy as an electrical charge. The value is expressed in microfarads (µF).
  • Inductance: describes the ability to store energy created by electric current flow as a magnetic field. The value is expressed as nanohenries (nH).

Analysis notifications

When you cancel an analysis the table populates with data up to the point of cancellation. A yellow triangular badge displays next to any path with an incomplete analysis. To re-run the analysis, right-click the signal path and click Re-run analysis. In the context menu use Clear signal to delete the results and Collapse all children to view only full paths in the table.

If the analysis returns errors a red diamond shape badge displays next to paths having errors. Double click the path row to view the path in the canvas.