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Liberate not able to characterize at low supply voltages

marten

Hi there,

we would like to characterize standard cells for low supply voltages (e.g. 200mV).
While the same cells get characterized correctly at 1V, they all fail at 300 mV.

For a d latch the follwing kinds of errors occur (even at vdd=600mV) during characterization phase:

Performance statistics for DL_X1: Spectre cpu time = 75.9 seconds, total cpu time = 76.2 seconds, wall clock time = 63.0 seconds.
ERROR (LIB-52): On arc 'DL_X1 CLK f D r setup_falling rise_constraint', the constraint search failed to find a solution within the search range. The cell will be marked as failed and the .lib will contain 'constraint_failed_value'.  To debug, save and review the simulation results using extsim_save_passed and extsim_save_failed. Possible causes include: constraint_delay_degrade too large; constraint_delay_degrade_abstol too large; constraint_search_bound too small. Modify the constraint parameters and rerun.
ERROR (LIB-52): On arc 'DL_X1 CLK f D f setup_falling fall_constraint', the constraint search failed to find a solution within the search range. The cell will be marked as failed and the .lib will contain 'constraint_failed_value'.  To debug, save and review the simulation results using extsim_save_passed and extsim_save_failed. Possible causes include: constraint_delay_degrade too large; constraint_delay_degrade_abstol too large; constraint_search_bound too small. Modify the constraint parameters and rerun.


And when writing out the .lib file, this kind of errors occour for boolean logic:

*Error* (write_library) : Invalid ecsm data found at points indexed at [ 0 1 2 3 4 5 6 7 8 9 10 ] in rise_transition for cell:NAND2_X1 pin:Z related_pin:A when:"". Only the indices without any invalid data will be output to the library for this ecsm waveform!!
The invalid data may be caused by waveform can not reach full power railPlease check the design and/or char option setings


Has anybody else encountered these errors?
I would highly appreciate each hint for solving this issues.

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