Latest update: 7/8/2024

Relevant product(s): Analog FastSPICE
Operating systems: Linux RHEL 7 and above
Versions affected: All
Relevant area(s): Simulations

Summary

Guide of AFS eXTreme such as:

Introduction

In AFS simulations, afsmode is the accuracy and performance settings. The higher the accuracy the lower the performance, vice versa. However, in the latest small-geometry technologies, post-layout design especially in analog design, verification accuracy cannot be easily compromised.

AFS eXTreme (AFS xt) is the newer feature, which directly focuses on improving simulation efficiency and capacity during verification, with minimal impact on accuracy. AFS XT performance improvements are achieved using a new solver and new reduction techniques. While the greatest runtime improvements can be expected with transient simulations, there are no limitations on which analyses can be used during a design’s verification.

There are 3 levels of accuracy & performance in AFS xt, red has the highest accuracy, green is intermediate, blue has the highest performance.

Launching AFS eXTreme From the Command Line

There are two command line options:

• a general option –xt,
• post-layout adjustment option –xtl.

Example:

afs netlist [–xt red|grn|green|blu|blue]  [–xtl red|grn|green|blu|blue]

3 accuracy/performance options for AFS eXTreme command:

–xt, –xtl	Extraction	Target Accuracy	Benefiting Analyses
red	RCC	Same as AFS. (Best accuracy)	Transient, Transient Noise, all RF.
grn	RCC or RC	Within 1%/1ps/3dB of AFS. (Intermediate)	Transient, Transient Noise, all RF.
blu	RCC or RC	Within 5%/5ps of AFS. (Best performance)	Transient.

xt

• –xt red
  • Optimize performance with a comparable accuracy to default AFS.Automatically apply –xtl red if –xtl is not used.
• –xt grn|green
  • Optimize performance within a target accuracy of 1ps/1%/3dB.
  • Automatically apply –xtl grn if –xtl is not used.
• –xt blu|blue
  • Optimize performance within a target accuracy of 5ps/5%.
  • Automatically apply –xtl blu if –xtl is not used.

xtl

• –xtl red
  • Optimize the post-layout design without applying reduction. This is most efficient on RCC extractions, with no impact on accuracy.
• –xtl grn|green
  • Optimize the post-layout design applying a conservative level of reduction. This is targeted at RC or RCC extractions and has a target accuracy of 1ps/1%/3dB.
• –xtl blu|blue
  • Optimize the post-layout design applying a higher level of reduction. This is targeted at RC or RCC extractions and has a target accuracy of 5ps/5%.

Note that–xt grn is automatically applied if –xt is not used.

Impact of AFS eXTreme on AFS simulations

• When you use –xt or –xtl, below options are disabled:
  • –afsmode
  • –performance
  • –parasitics

• The following user-specified options are ignored unless the command line option –xtoverride is used:
  • –abstol
  • –iabstol
  • –reltol, unless set by param_vec.
  • –vabstol
  • –vnto
• In Transient Analysis, the following user-specified options are ignored unless the command line option –xtoverride is used:
  • –errpreset
  • –maxiters
  • –maxstep, unless set by param_vec.

Useful references

https://docs.sw.siemens.com/en-US/doc/908970151/202401010.afs_useref/id3100ad81-6c62-415e-8d16-169c4cdd3efa

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