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Re-characterizing a tap-less cell library (Cadence Liberate)

anurans

Hi All,

I want to re-characterize the existing library to a lower supply voltage. I have been provided the extracted (with parasitics) netlist (.cir) of this tap-less cell library by the vendor. 

> I generated the cell template file from existing .lib in .tcl format which contains cell definitions, delay/power templates with slew/load indices.

> The provided netlist however contains the VBN/VBP contact ports (along with its parasitics) which are not available in generated template (I assume the earlier characterization was done by connecting well contacts to the supply rails accordingly / or atleast that's what I'd do if I create a lib for my custom made cells).

> In this condition, re-characterization is not possible as Liberate does not see VBN/VBP in cell definitions of the template. Is it possible to indicate "Liberate" that those well contacts should be connected globally to respective supply rails during the characterization ?

> When doing the characterization, are those slew values for the given loads automatically re-calculated for the new supply voltage ?

Thanks

Anuradha

Parents
  • Guangjun Cao

    1. if you want the new library to have exact the same arcs, use -verbose in the write_template command, and -user_arcs_only in char_library command;

    2. PG pins are not written out during write_template. users have to use set_vdd/gnd or set_pin_vdd/gnd to declare/define the PG pins and association of pin/PG-pins;

    3. if your reference library has normalized waveform, you can write out this and re-use it for re-characterisation. slew/load index tables are not necessarily related to supply for a give corner. If you want the tool to auto-calculate the index table, you need to specify the min/max_transition of your design and minimum input capacitance, which can all be corner dependent as your cells' behavior. -auto_index is also needed. you can also use -driver_waveform to include the normallized waveform in the generated library. Some STA tools use this information, which can improve the correlation between Spice simulation and STA analysis results.

Reply
  • Guangjun Cao

    1. if you want the new library to have exact the same arcs, use -verbose in the write_template command, and -user_arcs_only in char_library command;

    2. PG pins are not written out during write_template. users have to use set_vdd/gnd or set_pin_vdd/gnd to declare/define the PG pins and association of pin/PG-pins;

    3. if your reference library has normalized waveform, you can write out this and re-use it for re-characterisation. slew/load index tables are not necessarily related to supply for a give corner. If you want the tool to auto-calculate the index table, you need to specify the min/max_transition of your design and minimum input capacitance, which can all be corner dependent as your cells' behavior. -auto_index is also needed. you can also use -driver_waveform to include the normallized waveform in the generated library. Some STA tools use this information, which can improve the correlation between Spice simulation and STA analysis results.

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