9 

Static Power Grid Calculator

This chapter describes how to analyze the effects of parasitics on power net wiring, without performing a full simulation, using the Virtuoso^® UltraSim^™ static power grid calculator.

Analyzing Parasitic Effects on Power Net Wiring

The static power grid calculator can be used to calculate all pin-to-tap or pin-to-subnode resistances based on the net description from a DSPF or SPEF file (a pre-layout netlist file is not required). The analysis assumes that all pins are connected, and an ordered list of instance pins or taps and their resistances is reported.

To invoke the static power grid calculator, use the -r command line option accompanied by a command file. The command file contains all of the calculator control and data filtering options. See Figure 9-1 for more information about inputs to the static power grid calculator.

Figure 9-1  Static Power Grid Calculator Input

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The analysis results are printed into text files (two files per net) with filename prefixes specified in the command line option. The -rout filtering routine is used to filter existing output data without running the calculator again. See static power grid calculator output in Figure 9-2.

Figure 9-2  Static Power Grid Calculator Output

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ultrasim -r

Spectre Syntax

ultrasim -r <resistance_command_file> -o <output_prefix> [+log <log_file_name> |

-log]

SPICE Syntax

.ultrasim -r <resistance_command_file> -o <output_prefix> [+log <log_file_name> |

-log]

Arguments

 

-r	Enables static power grid calculator
-o	Output files prefix
+log	Prints log on display and into a specified log file
-log	Calculated resistances are not copied to a file

Command File Options (resistance_command_file)

 

file <file_name>	DSPF or SPEF filename.
net <net_name>	Defines power net for calculation. Net needs to be defined in DSPF *|NET section of file. Multiple net statements are allowed. net_name is case sensitive.
addnetpin <net_name> <node_name>	Converts subnode to pin in net <net_name>.
netdeletepin <net_name> <node_name> [<node_name>]	Converts pins to subnode.
subnode <subnode_pattern> [<subnode_pattern>]	Converts subnodes to tap nodes.
netdeletetap <net_name> <node_name> [<node_name>]	Convert tap nodes to subnodes.
ipin <pin_pattern>	Specifies tap nodes for resistor calculation. All other tap nodes are converted to subnodes.
layer0ohm <layer_name> [<layer_name>]	Resistors with specified layer names are shorted.
layerfactor <layer_name> <scale_factor>	Resistors with specified layer name are scaled by factor. Multiple layerfactor options are accepted.
rmin <value>	Resistors with a value less than rmin are shorted.
sortby <sortkey>	Specifies sorting method where sortkey can be r, w/l, or rw/l.
report <report_options>	Inserts -rout filtering options into command file (see <report_options> for definition).

Filtering Routine

The -rout command line option allows you to filter results from the static power grid calculator analysis without having to rerun the calculation. The calculator reads the existing -r output files and applies filtering to the data stored in these files.

Spectre Syntax

ultrasim -rout <prefix_of_rout_file> <report_options> [+log <log_file_name> |

-log]

SPICE Syntax

.ultrasim -rout <prefix_of_rout_file> <report_options> [+log <log_file_name> |
-log]

Arguments

 

-rout	Enables filtering routine
<prefix_of_rout_file>	Defines output file prefix
<report_options>	Defines options filtering
+log	Prints log on display and into a specified log file
-log	Calculated resistances are not copied to a file

Arguments for Data Filtering (report_options)

 

-pat <"pattern_with_wildcards">	Limits report to nodes matching specified pattern
-nr <integer_value>	Limits number of output nodes (no limit if not defined)
-minr <double_value>	Reports only nodes with Reff>minr
-maxr <double_value>	Reports only nodes with Reff<maxr;
-xmin <value> -xmax <value> -ymin <value> -ymax <value>	Reports only nodes in specified region
-gdsmag <value>	Specifies geometry magnification where all coordinates are multiplied by <value> if <value> is positive, or divided by <value> if <value> is negative
-gdsunits <value>	Specifies geometry units within the DSPF or SPEF file
-rth <th_value>	Generates a file with the name <file_name>.0.report for nodes with Reff < rth and a file with the name <file_name>.1.report for nodes with Reff >= rth.

For tap nodes connected to a MOSFET gate, w/l is reported to be zero. If the source and drain of the same MOSFET are connected to the same net, w/l for this tap node is also reported to be zero.

Examples

In the first static power grid calculator example, the following Rescalc.config command file is used:

file cell.spf

net gnd

netdeletepin gnd gnd_1

subnode gnd:* vcc:*

rmin 0.01

sortby w/l

report -nr 1000 -minr 20 -pat*.SRC -pat*.DRN

net vcc

netdeletetap vcc x1/m2:drain x1/m4:source

addnetpin vcc vcca:1

The static power grid calculator is run using the following options:

ultrasim -r Rescalc.config -o res_examp

The static power grid calculator results are printed into the following files:

- res_examp-gnd.rout (non-filtered results)

- res_examp-gnd.minr20nr1000.rout (filtered results)

- res_examp-vcc.rout (non-filtered results)

- res_examp-vcc.minr20nr1000.rout (filtered results)

In the next example,

ultrasim -rout res_examp-gnd -o -nr 1000 -minr 5 -maxr 1000

a filtering routine is used on the res_examp-gnd.rout output file to filter out the first 1000 resistive paths with a resistance between 5 and 1000 Ohm. The filtered results are printed into the res_examp-gnd.nr1000minr5maxr1000.report file.