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Chapter 18. EM: NET-AN

The NET-AN tool from OEA is used to extract metal into equivalent RLCK netlists.

18.1. Parasitic Extraction

Parasitic extraction is a method of automatically modeling the electrical characteristics of a single or group of iNet(s) using a parasitic extractor. Cadence® defines parasitic extractor as a physical simulator that produced RLCK netlists. This type of extraction is the type of extraction common to silicon design styles.

The basics of the extraction flows have been covered in previous chapters. This chapter discusses specific issues unique to parasitic extractors. Parasitic extraction is typically used for iNets only. The only exception might be spiral inductors if the parasitic extractor can accurately model them.

18.1.1. Setup Issues

Selecting iNets for Extraction

See “Electrical Net (iNet) Elements” for techniques on how to select multiple iNets for extraction.

Extract Block

When using the EXTRACT block and using a parasitic extractor, there are several settings to consider.

  1. Simulator - choosing the wrong simulator can result in a very long simulation that you didn't intend. You can always cancel long simulations if necessary.

  2. Cell Size - the x and y cell size setting should be small enough to resolve the smallest line or via geometry. For shape-based extractors (like OEA), if the cell size is too big, the connectivity may not be correct. Currently 0.1um is a good setting.

  3. PortType - always leave at the default.

  4. Extension - this setting won't affect the simulation results, but will affect the size the EM structure draws for extraction. Currently, 10um is a good setting.

  5. NET-AN Options - Found on the NET-AN Options tab of the EXTRACT block when NET-AN is selected as the simulator. See “Options Dialog Box: NET-AN Options Tab” for option details.

STACKUP Block

For designers using parasitic extractors, their process is typically configured by a PDK, including the STACKUP block. The STACKUP block is typically located in the Global Definitions area.

If you need to work with your STACKUP block, the main issue is configuring the mapping properly, either using EM Layer Mapping or Line Type mapping. See “EM Layer Mapping vs. Line Types” for more information.

Parasitic Extractor Options

Each parasitic extractor has simulator specific options. You should first create your extraction document (see “Viewing EM Structures Before Simulation”) and view the options specific to the extractor being used.

18.1.2. Viewing Parasitic Extraction Results

Viewing the parasitic extraction results is best discussed using an example. Figure 18.1, “Simple 2um x 5um Line Routed between Two Rect Pins ” shows a very simple 2um x 5um line on the lowest level metal of a generic silicon process (used for demonstration purposes only).

Figure 18.1. Simple 2um x 5um Line Routed between Two Rect Pins

Simple 2um x 5um Line Routed between Two Rect Pins

Viewing the Netlist

After a parasitic extraction runs, you can view the resulting netlist from the Status window. In this simple example, the Status Window displays as shown in Figure 18.2, “Status Window after Parasitic Extraction Runs”.

Figure 18.2. Status Window after Parasitic Extraction Runs

Status Window after Parasitic Extraction Runs

There is a line for the extracted netlist information included for the netlist link. If you click on the link, a new window opens with the netlist as shown in Figure 18.3, “View of Extracted Netlist”.

Figure 18.3. View of Extracted Netlist

View of Extracted Netlist

Viewing Extraction Elements in Layout

You can also view the parasitic extracted element superimposed on the 3D view of the EM structure. Figure 18.4, “3D Layout of EM Structure with Extracted Elements Displayed” shows this view with the simple line example.

You can access this view by right-clicking the EM structure used for your parasitic extraction, and choosing Add Annotation. In the Add EM Structure Annotation dialog box, select Annotate > ERC as the Measurement Type and choose EXT_CKT3D as the Measurement. Add the measurement as shown in Figure 13.11, “Add Annotation to Display the Circuit Representing the Extracted Document”.

There are several controls to help show only specific elements of the netlist. In this example, you can see all the elements. In more complex extracted networks, the display is too difficult to understand without pruning the data.

Notice in the Add EM Structure Annotation dialog box, there is a Display values option. You can specify that each component display their Component Values, Component IDs, or Node Numbers. Figure 18.4, “3D Layout of EM Structure with Extracted Elements Displayed” shows node numbers that correspond with the netlist you can view, as shown in the previous section.

Figure 18.4. 3D Layout of EM Structure with Extracted Elements Displayed

3D Layout of EM Structure with Extracted Elements Displayed

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