How is the speed-power product of a logic family determined?

Propagation delay:The average transition delay time for the signal to propagate from input to output where the signal changes in value.Propagation delays are separately defined for LOW-to-HIGH and HIGH-to-LOW transitions at the output.We also DEFINE enable and disable time delays that occur during the transition between the high-impedance state and defined logic LOW or HIGH states.Generally, propagation delay will be in the order of nanoseconds (ns). Power dissipation:The power dissipation of a logic gate is the power required by the gate to operate with a 50% duty CYCLE at a specified frequency.Power dissipation generally EXPRESSED in milliwatt (mW). Speed-power product:A common means for measuring and comparing the overall performance of an IC family is the speed-power product.Speed-power product is defined as the product of propagation delay time in ns and power dissipation in mW.It is also called a FIGURE of merit.Normally, the minimum values of the speed-power product are desired for better performance.