Background

PET (Power Evaluation Tool) is a software tool to evaluate the power consumption of a CMOS circuit realized with standard cells. PET interacts with the COMPASS tools and provides accurate evaluations with a small time overhead. Although PET can be run over different formats (i.e. different ECAD tools), COMPASS is at the moment the only design tool supported.

The power consumption in a CMOS cell is proportional to the output load, to the frequency of the switching and to the short-circuit currents. In more complex cells and sequential cells also the switching of the internal nodes, not affecting the cell's output, dissipates power. The model used in PET doesn't take into account transitions occurring in internal nodes. The expression used by PET to calculate the power dissipated by a CMOS circuit realized with standard cells is:

f0 (frequency) and n0 (number of transitions) are designer's choices.

Eint (internal energy per transition), Ecl (energy dissipated per clock cycle) and VDD (power supply voltage) depend on the Standard Cells Library.

C (load capacitance) depends on the layout.

ni and ncl (number of transitions in the nodes) depend on the result of the simulation and on the choice of the test vectors.

For more detail see PET references.

The figure shows the work flow of PET.

The steps to be taken when using PET are:

Extract the netlist from the layout (i.e. file [nle])

Run PET analyze on the netlist [nle]

Add file [mon] to the input stimuli (generate file [csm])

Run COMPASS sim and obtain file [trc]

Run PET ttgen to generate file [trn]

Run PET calpot to calculate the power dissipation