Product Documentation
Voltus-Fi Custom Power Integrity Solution L User Guide
Product Version IC23.1, August 2023

6

IR Drop Analysis Results

Overview

Voltus-Fi-L uses the results of the simulation performed using the vavo-db or the parameter storage format (PSF) data to perform IR drop and EM analysis. The software provides both batch mode and GUI support for performing these analyses.

Signal Net IR Drop Analysis

By default, IR drop analysis can only be applied to power nets, which are nets driven by DC or constant voltage sources. The advanced feature, signal net IR drop analysis, lets you perform IR drop analysis on signal nets, which are nets that are not connected to any DC or constant voltage source.

In the signal net IR drop analysis, the maximum or average IR drop is reported using the analysis=[sigvmax sigvavg] statement in the EMIR control file (emir.config).

For details, see the Signal Net IR Drop Analysis section in the “IR Drop Analysis Results” chapter of the Voltus-Fi Custom Power Integrity Solution XL User Guide.

Solid Shape Highlighting

The rail analysis plots that are displayed on the Virtuoso Layout can be viewed as either stick diagrams or solid shape highlights. In the solid shape display, the plots highlight the full shape of the presistors, while in the stick diagram display, the presistors are connected through thin lines over the layout shapes.

The solid shape display is more useful for designers because it allows them to see the shapes that are failing the analysis. There are two flows for solid shape display. You can either specify the DFII layermap file or the QRC run name for viewing solid shape display for plots. When you specify the QRC run name, the plots are displayed based on the shape database generated by Quantus QRC.

For details, see the Solid Shape Highlighting section in the “IR Drop Analysis Results” chapter of the Voltus-Fi Custom Power Integrity Solution XL User Guide.

Displaying Finer Color Gradient for Selected Layers in IR and EM Plots

In the DFII layermap flow, for solid shape display of IR/EM violations on the Virtuoso layout, Voltus-Fi-L locates all the nodes lying on a shape and then colors the shape with the worst violation value among all resistors connected to these nodes.

However, sometimes resistors do not align well with the shapes used to display the violations. This may be because the shapes are large and have multiple nodes and resistors. Voltus-Fi supports a finer display of the color gradient for violations in different segments of such layers. The shape polygons are split into subpolygons and then the subpolygons are colored with the worst violation value for all resistors connected to the nodes in the split shape. This feature is turned on by default for all layers. However, you can select specific layers to view their finer gradient instead of viewing for all layers.

For this, specify the DFII Layermap file and then click the Finer Gradient button provided on the IR or EM tabs of the IR/EM Results form. In the Finer Gradient Layer Selection pop-up, click Deselect All and then select the PGDB layers for which you want to view finer gradient. For details of the steps involved, see Displaying Finer Color Gradient for Selected Layers in IR and EM Plots in the “IR Drop Analysis Results” chapter of the Voltus-Fi Custom Power Integrity Solution XL User Guide.

Loading the DFII Layer Map File by Default

You can specify the path to the DFII Layer Map file in the GUI for both IR drop and EM analysis results in the DFII Layermap file field provided in both the IR and EM tabs of the IR/EM Results form. You can also use a variable to load the layer map file by default. For this, specify the DFII layer map file in either the .cdsinit or the .cdsenv file by using the vfiDfiiLayerMapFile environment variable. The syntax and example of specifying the path to the DFII layer map file is provided below.

Setting a Layer Index for Displaying Violations on the Layout

Voltus-Fi-L creates layers for displaying the EMIR violations when you plot them on the Virtuoso Layout. By default, the software uses more than a hundred layers for displaying violations. It creates these layers by using a layer index value or layer number that is equal to or greater than 256.

However, if you are already using the same layer number as that used by Voltus-Fi-L, a layer number conflict will occur and a warning will be issued. To avoid this warning, specify a different value for the layer number. You can specify the layer index value in either the .cdsinit or the .cdsenv file by using the vfiLayerIndex environment variable. The syntax and example of specifying the variable is provided below.

The IR Drop Analysis Flow

In this section, the use model for the IR drop analysis flow is detailed for batch mode and GUI mode.

The IR Drop Analysis Batch Mode Flow

The IR drop analysis batch mode flow can be run using either the EMIR configuration file used in Voltus-Fi-XL or the command file used by legacy (VPS-L). The complete details of the batch mode flow are covered in the “Batch Mode Execution” chapter.

For details of the Voltus-Fi-L batch mode flow, see the following sections in the “Batch Mode Execution” chapter:

For details about migrating from legacy (VPS-L) to Voltus-Fi-L in batch mode, see Migrating from Legacy (VPS-L) to Voltus-Fi-L in Batch Mode in the “Batch Mode Execution” chapter.

The batch mode IR drop analysis flow involves the following key tasks, which are detailed in the sections below:

Loading the IR Drop Analysis Results

When the legacy (VPS-L) command file is used for running Voltus-Fi-L in the batch mode, you can load the IR drop analysis results by writing the following command in the vfibatch command file:

load_ir_results_extview -i cmd_file

Where,

cmd_file is the same batch file that is used in the legacy (VPS-L) batch mode execution.

Printing the IR Drop Analysis Reports

When the EMIR configuration file is used for running Voltus-Fi-L in the batch mode, the IR drop analysis report, #.rpt_ir, is generated automatically by the tool.

When the legacy (VPS-L) batch command file is used for running Voltus-Fi-L in the batch mode, the command, print_ir_report, is used to generate the IR drop analysis reports. This is the same command that is used to print IR drop analysis reports in Voltus-Fi-XL.

The syntax of the command is as follows:

print_ir_report
-net {all_power | netname}
-type {ir | iravg | rc | rcavg | rcrms}
[-threshold threshold_value]
-filename output_file_name]
In the -type parameter, only the analysis types listed in the syntax above are supported in the Voltus-Fi-L flow.

For details of the above command and its parameters, see print_ir_report in the “Batch Mode Execution” chapter.

Sample Command Files for IR Drop Analysis

Sample command files used for running the IR drop analysis in batch mode in Voltus-Fi-L are provided below.

The IR Drop Analysis GUI Flow

To view the IR drop analysis results in Voltus-Fi-L, ensure the following are provided:

The following topics are covered in this section:

Viewing the IR Drop Analysis Results

Follow these steps to view the IR drop analysis results:

In the Results group box:

Displaying and Querying EMIR Results

Voltus-Fi-L lets you specify the plot display settings for the IR drop and EM plots that are displayed on the Virtuoso layout.

The plot display options include a Min - Max slider that lets you customize the range of violations you want to view. A continuous RGB gradient is used to highlight the worst violation regions in the design. The vast range of color options provided by the RGB gradient makes it easier to view a range of violations on the layout.

In addition to specifying settings for the plots displayed on the layout, there are options to query the layout for viewing specific violations. The results of the query are highlighted in the EM/IR tab of the Annotation Browser.

You can also compare reports that are generated for different analysis types either in the GUI or the batch mode. You can compare any two reports; one GUI and one batch report, two GUI reports, or even two batch reports. For this, Compare Report button is provided in the Display form.

For detailed descriptions of the display options and query feature in the GUI mode, see Displaying and Querying EMIR Results in the “IR Drop Analysis Plots” chapter of the Voltus-Fi Custom Power Integrity Solution XL User Guide.

The section, Displaying and Querying EMIR Results includes the following topics and subtopics:

For the batch command flow of the Query feature, see Batch Command for RON Reports in the “Batch Mode Execution” chapter.

Types of IR Drop Analysis Plots

Following types of IR drop analysis results plots are available in the list in the Rail Analysis field in the IR/EM Results form.

For details of the above plots, see Types of IR Drop Analysis Plots in the “IR Drop Analysis” chapter of the Voltus-Fi Custom Power Integrity Solution XL User Guide.
The following IR drop analysis plots, currently supported in Voltus-Fi-XL, are not supported in Voltus-Fi-L:

Plotting the Least-Resistive Path

The least-resistive path (LRP) plot lets you identify the weakly-connected instances in the design during early stages of power planning. The resistance for an instance pin is calculated as the total resistance along the least resistance path. If an instance has multiple power pins connected to the power grid, the LRP plot uses the pin with the worst (highest) resistance value to plot the instance-based data. This plot highlights the current path for the selected instance to the voltage source. A long LRP usually results in high resistance and potentially high voltage drop.

In addition to identifying and displaying the worst IR drop violations, the LRP feature in Voltus-Fi-L lets you plot LRP on demand for any node. You can view the LRP for any high IR drop node by selecting it on the layout. There are two options provided in the GUI, Get Layout Node and Get Marker Node, to let you select a node on the GUI and view its LRP, and to select an object in the Annotation Browser and view the LRP for the node on the selected marker. For details, see The LRP Browser and Displaying LRP for the Node on the Selected Marker, respectively.

The use model for LRP analysis is detailed below.

To view the LRP plot for a net, perform the following steps after loading the IR drop analysis results:

The LRP Browser

The LRP Browser tab lets you specify the nets, layers, and nodes for which you want to view the LRP plots. The various options provided for this tab are detailed below.

Voltus-Fi-L provides support in the form of tips about the information to be filled out in the various fields in the LRP Browser form. This tooltip appears when you hover the pointer over a field in the form. This is shown below.

Figure 6-9 Tool Tips for LRP Browser Tab

To start, click the LRP Browser tab of the IR/EM Results form. The form shown below opens.

Figure 6-10 LRP Browser Tab of the IR/EM Results Form

There are two group boxes in this tab, the LRP Paths and Resistance Path.

Resistance Path Group Box Table Information

The Resistance Path table lists all the resistors in the LRP path for the node selected in the Node ID - Node Name table. You can click any row to highlight the resistor in the layout window.

A section of the Resistance Path table is shown in the image below. The details of the column information is provided subsequently.

Figure 6-15 Information in the Resistance Path Table

The following information is provided in the table:

Shorting Layers for LRP Analysis

While computing LRP for a node or instance, you can short specific layers. When you do this, all the resistance on the specified layer is shorted. That means, the LRP display shows a value of 0 for all resistors on the shorted layer. This is shown in the images below.

When you click Shorted layers, the Filters pop-up window opens. In this window, select the layer you want to short. You can short multiple layers.

For example, in the image below, layer Metal1 or mt1 is shorted.

Figure 6-16 Specifying the layers to be shorted for the LRP Analysis

When a layer is shorted, the resistance value information in the Resistance Path group box shows a value of 0 in the R val (Ohm) column for all the resistors on that layer. For example, in the image below, the LRP value for resistor rf147 on layer mt1 is 0.

Figure 6-17 LRP Value for Resistors on the Shorted Layer

Displaying LRP for the Node on the Selected Marker

You can display the LRP for a node on the selected marker in the Annotation Browser. When you select a violation marker in the Browser, it is highlighted on the layout. If the marker is associated with a node name, you can view the LRP for the node.

The steps are detailed below.

Generating EMIR Analysis Reports in Voltus-Fi-L

The following topics are covered in this section:

Reports Generated Using the EMIR Control File

You can generate both textual and html reports for EMIR results in Voltus-Fi-L from the simulation results by specifying the EMIR control file (emir.conf), the EMIR database file, and the output directory. In the EMIR control file, the emirutil command’s report option is set to text or html depending upon the required output.

For details, see Reports Generated using the EMIR Control File in the “IR Drop Analysis” chapter of the Voltus-Fi Custom Power Integrity Solution XL User Guide.

For details of the supported EMIR control file options that can be specified, see EMIR Control File Options Supported in Voltus-Fi-L in the “Batch Mode Execution” chapter.

You can also see the EMIR Control FIle Options Supported in Voltus-Fi-XL in the “Data Preparation” chapter of the Voltus-Fi Custom Power Integrity Solution XL User Guide.

For details on how to specify variables using the emirutil command in the EMIR control file, see Using the emirutil Command in the EMIR Control File in the “Variables” chapter.

Default Reports Generated by Voltus-Fi-L for EMIR Analysis

By default, Voltus-Fi-L generates the following reports for EMIR analysis:

For details of the report formats and sample reports, see Default Reports Generated for EMIR Analysis in the “IR Drop Analysis” chapter of the Voltus-Fi Custom Power Integrity Solution XL User Guide.

RLRP Report

RLRP analysis report (RLRP.rpt) includes the LRP values of the instances or tap-nodes of the specified net.

For details of the report format and sample report, see RLRP Report in the “IR Drop Analysis” chapter of the Voltus-Fi Custom Power Integrity Solution XL User Guide.

Reporting On-Resistance Values

Overview

Voltus-Fi-L reports the on-resistance (RON) values for all layers and devices between specified pairs of pins in a design. The software reports the combined resistance contribution of both pins in the pair and the contribution from each pin. The resistance values are reported in ohms.

For this feature, report_vfi_L_ron command has been provided. For details, see report_vfi_L_ron.

The flow is currently enabled only after setting the variable shown below:

setenv ENABLE_VFI_L_RON_DATA_READING_FROM_PSF t

Generating the RON Report

This flow is supported only in the batch mode. To enable this flow, perform the following steps:

Example

These set of commands are included in the main command file, main.cmd.

Contents of the extViewExtraCmdFile

The extracted-view data is loaded through the cmd_file, extViewExtraCmdFile. A sample command file for EM analysis is shown below.

;vsa batch mode command file
;common commands 
_vsa_extracted_lib_cell_view “amsPLL” “vco” “av_extracted_sol”
_vsa_testbench_lib_cell_view “amsPLL” “TB1_vco_single” “schematic”
_vsa_simulation_directory “/custom/TB1_vco_single/spectre/schematic/”
_vsa_pres_cellname “presistor”
_vsa_analysis_data “TRANSIENT”
;commands for EM analysis
_vsa_qrc_run_directory “/custom/WORK/AV/LVS_emir”
_vsa_em_data_file “emDataFile.txt”
;_vsa_analyze_em "0" "1n"
_vsa_analyze_em
exit

Output

The RON report includes the following information:

Sample Pin-Pair File

D S

Where D and S are names of pins separated by a space.

Sample RON Report

A sample RON report is shown below.

Figure 6-19 Sample RON Report


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