A simple way to estimate the total power consumption of memories in an SoC

Memories are increasingly occupying more area in today’s SoCs. So, it is imperative to have an early estimate of the total power consumed by the memories. Memory power consumption can be divided into two components:

• Leakage power – consisting of memory bitcell array leakage and memory periphery leakage
• Dynamic power – consisting of capacitive switching and crowbar current

Using a memory datasheet, you can gather all the leakage and dynamic current parameters that are needed to calculate the total power.

Leakage current parameters:

• Leakage_c_chipdisable - Leakage current of memory bitcell array when memory is disabled
• Leakage_p_chipdisable – Leakage current of memory periphery when memory is disabled
• Leakage_c_chipenable - Leakage current of memory bitcell array when memory is enabled
• Leakage_p_chipenable - Leakage current of memory periphery when memory is enabled

Dynamic current parameters:

• Icc_c_read – dynamic current of memory bitcell array during read cycle
• Icc_p_read– dynamic current of memory periphery during read cycle
• Icc_c_write– dynamic current of memory bitcell array during write cycle
• Icc_p_write– dynamic current of memory periphery during write cycle

The total power can then be calculated using the following equation.

P_total_estimate = Vdd * (1-activity_factor) * (Leakage_c_chipdisable + Leakage_p_chipdisable) +

                                  Vdd * activity_factor * ( Leakage_c_chipenable + Leakage_p_chipenable) +

                                 Vdd * activity_factor * frequency * ((Icc_c_read + Icc_p_read + Icc_c_write +  Icc_p_write)/2)

To ensure you obtain correct results:

• generate the data with 1Mhz frequency
• generate the data with 100% activity factor

This equation will give you the total power estimate for one instance. In a typical SoC, there are hundreds or thousands of instances. To find out the total power consumed by all the memories in a SoC, you can enter the above parameters and the equation into a spreadsheet and do the calculation. Estimating the total power consumption enables you to identify the hotspots early in the design cycle. To save power you can now decide to reconfigure the memory instances or choose a different compiler  to generate hotspot instances.