04/22/23 Fractal TechnologiesConfidential

Fractal Technologies

Typical STD Cell Library Errors

04/22/23 Quality in Design Formats 2

Typical Cell Presence Errors

• Obsolete Cells– Cadence DFII has many times hierarchical cells that are not used

anymore. (Artefacts)– Double cell entries– Cells removed from Cadence DB still remain in other formats. (Verilog,

MilkyWay, Liberty, etc...)• Missing Cells

– Wrong database in cds.lib included. Hierarchical cells are missing.– Cells in the CDB do not exist in the other formats due to later added

cells not all Databases are updated or an older database is delivered– Documentation many times misses a cell

• Due to no formal checking method• Filler and alignment cells not consistent for the various DB’s

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Typical Terminals & Pins Errors

• Direction of the pins does not match– Input,Output, Bidirectional

• Pins are in the wrong layer• Uses busses instead of single pins

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Typical Label Errors

• Missing labels– Simply missing– Typing errors– Uppor vs lower case errors

• Labels in the wrong layer

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Typical Net Errors

• Missing net information– Due to copy actions in the Cadence Database Net information

may be lost.– Database corrupt…

• Busses used instead of single pins

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Typical Layout vs. layout Errors

• Modifications in the master Cadence Database not copied to GDSII or LEF

• 45 degrees not accurately enough in LEF

• Abstract not generated correctly

• Shifted polygons

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Typical Abutment Errors

• 1 grid shift • Missing boundary layer

• Layers do not touch the outline

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Typical Routability Errors

• Pins not on grid• Wrongly coded off-set

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Typical Functional Equivalence Errors

• Both active PRESET and SET yield different result over the various formats– Priority definitions wrong

• Mismatch between asynchronous and synchronous descriptions

• Missing functional description• Short circuit detection• Cont…

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Typical Functional Equivalence Errors

• Documentation errors– Due to missing formal checking. (Depends on human reading)

Datasheet

.lib pin(OA1) { direction : output ;

function : "(!M2|(M1&M0))" ;

pin(OA2) { direction : output ;

function : "(M2|(!M1&!M0))" ;

pin(Z) { direction : output ;

function : "!(M1^M0)" ;

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Typical Characterization Errors

• Last characterization entries all 0.• Delay decreases with increasing output load• Conditional vs non-conditional descriptions• Back-annotation errors

– Conditions don’t match string based• Obsolete default conditions• Non-paired setup and hold times• Swapping of Liberty file names ff, tt, vs ss

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Typical CCS Characterization Errors

• Cells do not have a single peak current

• Current curves have a “correction current” at the tail

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Typical ECSM Characterization Errors

• ECSM-curves have large deviations (20-300%) between ECSM and NLDM delay values

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Conclusions

• It’s better to check the STD Cell Library before using it