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The Interactive Length Tuning dialog
The Interactive Length Tuning dialog allows you to optimize and control net lengths by allowing variable amplitude patterns to be inserted for existing lengths on the current PCB document.
This dialog has two sections: the Target Length and Pattern. The Target Length section allows you to control the net length from a user defined length, the current net length or one of the length or matched net length rules. The Pattern section allows you to control the amplitude pattern of the net on the PCB document by varying the amplitude and the gap.
The Target Length Tuning dialog allows users to see all applicable rules and select the one to be used. If no rule is selected by a user, the rule with the longer max length will be used by default. Alternately, if the target lengths for two rules are equal, then the rule with higher priority will be used.
The title bar of the dialog displays the current net name and the old length.
The dialog is accessed by clicking Route » Interactive Length Tuning then pressing Tab while tuning a net's length. When length tuning Differential Pairs, click Route » Interactive Diff Pair Length Tuning. The dialog is the same for both options, except the From Net option is replaced with From Diff. Pairs when accessed through the second command.
The length tuning offers four approaches for specifying the target length. The length can be: manually defined, based on a net that has already been routed, based on a set of Differential Pairs, or defined by design rules. The grid area on the right side will update accordingly. Currently selected rules are highlighted in blue within the grid area.
Manual - enter the length in the Target Length field. The list on the right keeps track of the values you have typed in, so that you can use one again.
From Net - after selecting From Net you can choose a net from the list on the right. The length of this net will become the target, however, it will be overridden if there are more restrictive design rules defined.
From Diff. Pairs - lists the differential pairs and their lengths on the current PCB. The currently selected differential pair length value is shown in the Target Length field, along with a description.
From Rules - you need to have one or both of the Length and Matched Length design rules defined to use this mode. Altium Designer will then obey the most stringent combination of these rules.
Edit Length Rule - click to change the values used for the High Speed Length design rule. The From Rules option needs to be selected first.
Edit Matched Lengths Rule - Click to change the values used for the High Speed Matched Lengths design rule. The From Rules option needs to be selected first.
Target Length - displays the target length being defined by the rules. Note that the most stringent combination of the rules is used. The target length will be set to halfway between range values in rules.
Create Rules From Length - click to open the Edit PCB Rule - Max-Min Length Rule dialog, in which you can create length rules.
Clip to target length - enable to ensure that the final length does not exceed the target length. When enabled, the Amplitude and Gap values are automatically adjusted to achieve the target length.
Style - shows the current amplitude wave pattern. Click to view and select another pattern. There are three pattern styles: Mitered with Lines, Mitered with Arcs, and Rounded. The PCB Editor will attempt to match the target length by adding segments to the length according to the defined target length.
mm
or mil units. To specify the units when entering a number, add the mm or mil suffix to the value.
mil suffix
to the value.
mm or mil units. To specify the units when entering a number, add the mm or mil suffix to the value.Once you have launched the length tuning command, length tuning segments are added by moving the cursor along the routed net.
The interactive length tuning cursor provides you with information during the tuning process including before and current track lengths, as well as a graphical representation to gauge how close you are to the ideal lengths. The yellow cursor bars indicate the possible minimum and maximum lengths. The green bar indicates the target length, as determined from the applicable Matched Length and Max Length design rules, or the settings in the Interactive Length Tuning dialog. The sliding indicator shows how close you are to achieving a match.
The length tuning can be created from straight or arc segments, with full control over the amplitude, pitch, and corner radius, or miter.
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