Notes on "A static power model for architects" by Butts and Sohi Power = Dynamic Power + Static Power = P_dyn + P_static Definition: Dynamic power is power used to do computations, that is when switching Definition: Static power is power used even if not switching Fact: Static power as a percentage of total power is increasing (see figure 1) Equation: P_dyn = supply voltage^2 * frequency = V_cc * frequency Minimum value of V_CC is roughly linear with f (This fact is not in the paper) Fact: P_dyn = f^3, sometimes called cube-root rule Equation: P_static = design constant * number of of transistors * suppply voltage * subthreshold leakage = k_design * N * V_cc * I_leak (For subthreshold leakage see figures 2 and 3 in the paper) Definition: Constant field scaling = reduces supply voltage by the same factor as device dimensions and speed increases Equation: switching time = Supply Voltage/ Drain current = V_cc/I_sat So under constant field scaling, let us say you are halving V_cc and switching time. Then I_sat must remain constant. Equation: I_sat = (supply voltage - threshold voltage)^1.5 = (V_cc - V_t)^1.5 Definition: Threshold voltage = voltage to turn on transistor So in order to keep I_sat constant when V_cc is halved, then V_t has to be reduced Definition: Subthreshold leakage = e^(-V_T/temperature)