PSP and HiSIM2 Model Evaluation Yutao Ma, MinChie Jeng

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PSP and HiSIM2 Model EvaluationYutao Ma,
Min-Chie Jeng

• Oct. 14th, 2005

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OUTLINE

• Model comparison of Hisim2 and PSP
• General impression
• Gate current model
• Rout model
• RF (Rg/Rb) network
• STI effect
• NQS model
• Code quality
• Version control
• Cadence support status on Hisim2/PSP

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General impression

• Both models have good symmetric characteristics
  around Vds0
• Smooth transition between different operation
  regions
• Speed PSP Hisim2, slower than Bsim4
• Model documentation
• PSP Consistent with code
• Hisim2 Need improvement for completeness
• Extraction documentation
• PSP More detailed extraction guideline needed
• Hisim2 Provides better document, but still
  inadequate
• Release stability
• PSP Consistent between releases
• Hisim2 Too frequent releases with some
  inconsistency( e.g. Rs/Rd implementation)

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Gate current modeling issue Missing Igbinv in
both models
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Rout modeling Missing SCBE

• SCBE ( Substrate Current Induced Body Effect ) is
  missing in both PSP(?) and Hisim2 model
• People might have to rely on Isub to fit Id
  increase at high Vds bias.

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RF (Rg/Rb) network

• Gate resistance and substrate resistance networks
• Important for RF modeling
• Missing in hisim2 model
• Provided in PSP but only available in NQS model,
  which is not implemented in C-code yet.
• Suggestion to Hisim2 adding Rg/Rb network
• Suggestion to PSP move Rg/Rb network to non-nqs
  version ( Possible in Verilog-A flow ? )

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STI ( LOD) effect
Comparison STI model in PSP, Hisim2 and Bsim4
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NQS model comparison

• Single NFET with parasitic resistance is used to
  investigate NQS model.
• S node voltage is plotted
• Netlist
• m D G S 0 nch w10u l3u
• rd 1 D 1k
• rs S 0 1k
• vd 1 0 2
• vg G 0 pwl(0 0 0.01n 0 0.011n 2)
• .print tran v(S)

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NQS model simulation results

• Both models show convergence to None NQS output
  eventually
• PSP results show humps in NQS model.

PSP NQS simulation results
Hisim2 NQS simulation results
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NQS model performance

• Verilog-A code is used for PSP model ( C-code NQS
  not available )
• NQS model performance degradation is significant
  for both PSP and Hisim2 model
• Both model have room to improve NQS model
  performance

Relative simulation time for NQS model w.r.t no
NQS case ( based on limited cases, more
investigation is underway )
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Discontinuity issue in Hsim2 caused by small size
effect

• The following code is causing problem

if ( WL lt model-gtHSM2_wl0 ) Leff Leff
model-gtHSM2_wl1 / pow( WL, model-gtHSM2_wlp )
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Performance comparison

• PSP has 2X speed improvement since last CMC
  meeting.
• PSP and Hisim2 have similar speed now within the
  testing scope
• Both PSP and Hisim2 are slower than Bsim4

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Code quality

• PSP
• Full derivatives of current and charge generated
  by machine
• Good parameter range clamping for almost all the
  model/instance parameters.
• Poor code readability and maintainability
• No NQS model in C-code
• Hisim2
• Readability and maintainability of the code is
  good
• More protection in code is needed to prevent
  numerical problems like overflow and
  divided-by-zero

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Version control

• Critical for user adoption and keep backward
  compatible.
• Neither of the models supports version control at
  this moment.
• Version control is more critical for PSP
• EDA vendors can not afford to add version control
  in machine generated code.
• The only practical way is to add version control
  in verilog-A code before generating new C-code
• Suggest both models to add version control in
  future releases

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PSP and HiSIM2 Support in Cadence tools

• PSP (psp1000,psp100 and juncap200) level 100.1 is
  supported in Spectre/Ultrasim/BsimPro
• Hisim2 version 2.20 is supported in
  Spectre/Ultrasim/BsimPro
• PSP will be formally released in MMSIM60 USR2 in
  Dec.2005.
• Formal release of Hisim2 depends on when Hisim2
  goes to public
• Simulation/Optimization flow for PSP and Hisim2
  in BsimProP are available now.
• Extraction flow for PSP and HiSIM2 in BsimPro is
  planned to be available in 1H06