A layout engineer who studies signal integrity simulation.
When designing layouts, we need to control the impedance of layouts that encounter differential signals, such as USB and HDMI. Then we also need to follow the rules of electrical appliances when wiring. Set the differential requirements on the physical rules, and today I will summarize and share the differential pair settings in Allegro:
First: open the rule manager Constraint Manager
In the menu bar of Allegro, select Constraint in Setup, click the rule management at the bottom, or directly click CM in the shortcut toolbar, as shown in the following figure:
Step 2: Set Differential Pair
Find the bottom delay setting in Net in Electrical Rules, and then find the network to be added. Right-click on one of the networks and select Differential Pair in Create, as shown in the figure below:
After completing the above step, the Create Differential Pair dialog box will pop up. Find the differential network in the left Net and click the middle arrow to add it to the Diff Pair and Fill in the name of the differential pair, and finally click Create, as shown in the figure below:
Step 3: Add physical rules Physical line width:
Because we set the differential rules, according to different impedance requirements, the line width and spacing of the traces are different from other general traces, so a physical rule Physical is added here. First select Physical, then click All layers, right-click on the default rule and select Create Physical Set, as shown in the figure below:
fill in the name of the differential physical rule in the pop-up dialog box, and then modify different situations under the corresponding physical rule (each layer line width, minimum line width, maximum line width, etc.), in general, we can set the value in Line Width, as shown in the figure below: Then select
Net in Physical, find the differential pair we set, in Select physical rule 100 in the rule column on the right, so that the line width of our differential pair is set, as shown in the following figure:
Step 3: Add Spacing differential spacing:
The setting of the spacing is the same as the setting of the line width in the previous step. First establish the spacing rule, and then add the spacing rule to the differential pair. You can directly refer to the following figure: after completing the above steps, our differential rule is set.
Everyone You can go back to the design interface to try whether the setting is successful, as shown in the figure below:
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The above information is mainly compiled by myself in PCB design and Internet search
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