Modeling of SRAM Standby Current by Three-Parameter Lognormal Distribution

Measurements reveal that SRAM standby current follows a lognormal distribution where a location parameter is introduced, in addition to the well-known scale and shape parameters. The location parameter sets a threshold, indicating that the sample value must be bounded above by some non-zero minimum. This is of tremendous importance for the modeling of the SRAM standby current, since in the probability plot, the threshold leads to downward sloping trends at both ends which match the measurements fairly well. Further, it is shown that the three-parameter lognormal distribution remains valid for a standby current reduction scheme in a sleep mode by source line self bias.