The Differential Pair Skew Rules dialog is used to specify the minimum paired length and maximum length difference (skew) between the two tracks in the differential pair.
The general rule matching mechanism is described here.
One way to achieve the required length skew is to use Serpentine to lengthen one side of the Differential Pair. View the Serpentine Routing Overview page.
Shortcuts
Menu: Setup
Default Keys: T
Command: Technology
Locating this option
Available from: Setup menu > Technology option > Rules - High Speed - Differential Pair Skew page
Using the dialog
On selection, the Technology dialog opens, select Differential Pair Skew. The existing Differential Pair Skew rules for the Technology being used will be presented.
Navigation
The buttons to the right side of the dialog are used to navigate the grid, the general common buttons are detailed on the Technology Navigation page.
Where Used
Using the Selected button will report where the selected rule is used in the Technology. Likewise, using the All button will report where all the rules in this dialog are used in the Technology.
Using the editing pane
Attribute Name
Use the Attribute Name to define how the rule will be matched. From the drop down list, choose from
built in names which includes
Match Value is used to match the rule against the Differential Pair name or the Attribute name
defined. Wildcards are acceptable in the value, for example HSE*. Use the small button
next to the Match entry to display the
Wildcard Wizard dialog.
The appropriate skew rule is found for each differential pair by working down the list of rules until
the first match is found. Hence, the order of the rules is important. A match is when the specified
Attribute Name and Match Value match an attribute of a differential pair, or an attribute
on both nets of a differential pair. So the differential pair or nets must have the given attribute,
and it’s value must wildcard match the value.
In particular, you can match the inbuilt attribute
Min % Paired specifies the minimum percentage of the total track length which must be paired. Paired means that it should be parallel and at the gap specified by the Differential Pair Gap rule, or otherwise, the track to track spacing rule. The percentage is calculated using unadjusted lengths (see below for adjustments applied for length difference).
Max Length Diff specifies the maximum difference (or skew) of the total track length of each side
of the differential pair. This length includes any length adjustments caused by
Track Length Factor,
Layer Change Length or
Differential Pairs in the Rules Spreadsheet
The Rules Spreadsheet provides information about the differential pairs in the design. This displays the rules and actual lengths as they are edited in the design. This is presented to you in a dockable modeless bar.
Export and Import CSV
Use the Export CSV button to export the data in your PCB design into a CSV format file. Using the Export CSV option will provide you with a formatted template ready for you to edit in your own data.
Use the Import CSV button to import data back into the PCB design using a CSV format file.
The data in the file represents a spreadsheet of dialog contents with the data headings along the top row.
Units
The Units button allows you to locally switch between Metric and Imperial units whilst in this dialog. Once the dialog is closed, the units revert back to the original design units. If switching to different units to the design units, the value typed will be converted when you next enter this page.
Related Topics
Serpentine Routing Overview | Technology Overview | Using Dialog Grids | Differential Pairs Overview | Differential Pairs | Differential Pair Gap Rules | Spacing Rules | Layer Change Length | Rules Spreadsheet | Design Rule Check | Export CSV | Import CSV