Where To Find This Example
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Viewing iNet Parasitics
This example shows several techniques designers can use to estimate the parasitics (R,L,C or K) of the Intelligent Nets (iNets) used in their design. The process of extraction allows these parasitics to be included while simulating the circuit. However, many times designers want to know what the approximate parasitic values are.
This example will show you two different techniques to see your parasitic values in your iNets. The first is a layout annotation that will show you a single R and C per iNet. The second is to perform your parasitic extraction and then view the parasitics that were created superimposed on the 3D layout of the extraction layout.
In this discussion, we will discuss the following properties of an iNet:
1. iNet - complete interconnect metal for a single node in the circuit. An iNet can be made up of one or many routes.
2. Route - part of an iNet that is created during one editing operation. A route can be made up one or many segments.
3. Segment - a single section of a route, this is a single straight line on the same metal layer created with each mouse click when implementing an iNet.
The INET_RC annotation allows you to view your iNet parasitics on the layout for the circuit. This is a very simple calculation for each iNet to get an effective resistance and capacitance for each iNet. These values are calculated from the geometry of each iNet segment and resistance (resistance per length and per via) and capacitance (capacitance per area and capacitance per edge) values derived for the technology. The values are then annotated on the layout.
There are two schematics in this example, "Many_Routes" and "One_Route". The difference between the two layouts is that the iNet routing between the two resistors was done two different ways. The "One_Route" iNet has only one route with 5 segments. The "Many_Routes" iNet has 5 routes with each route having only one segment. If you select the iNets in both layout can see that in "One_Route" layout, the selection will highlight all segments of the iNet where for the "Many_Routes" layout the selection will only highlight one segment of the iNet.
View the layouts for each and you will see resistors and a capacitor superimposed on the layout. You get one resistor per route and one capacitor per iNet. You can see from the two layouts how this annotation changes based on how you implement your iNet. Once you change your iNet these values will update immediately. Try changing an iNet in either layout and see how the annotation changes.
You add this annotation by right mouse click on any EM structure used for extraction in the project browser and select Add Annotation. From the Measurement column, select INET_RC. You then have various options on how to display this annotation.
The EXT_CKT3D annotation allows you to view your iNet parasitics on the 3D layout of the extracted layout. Now, you are viewing each parasitic element created during the parasitic simulation. This is different than looking in the extraction netlist since each value is drawn in the 3D layout at the right physical location for that particular parasitic.
An extraction was setup for both schematics in this example, the EM document "Multiple" is the extraction for the "Many_Routes" schematic and the EM document "Single" is the extraction for the "One_Route" schematic.
After you simulate this example, you will see these parasitics in the 3D layout only for the extraction layouts.
You add this annotation by right mouse click on any EM structure used for extraction in the project browser and select Add Annotation. From the ERC Measurement Type, select EXT_CKT3D Measurement. You then have various options on how to display this annotation. Typically all of the extracted elements make this view too busy, so you might want to start out with only some of the options turned on.