The figure of merit of logic family is often measured in the unit of: 

Concept:

The figure of merit = Propagation Delay × Power Dissipation

For the best IC operation, FOM should be as small as possible.

Units: ns × mW

= pJ (pico Joule)

Propagation delay (tpd­):

\({t_{pd}} = \frac{{{t_{PHL}} + {t_{PLH}}}}{2}\)

tPHL = delay time in going from High to a low logic

tPLH = Delay time in going from low to High logic

Power dissipation (PD):

PD(avg) = Icc × Vcc

VCC = power supply

ICC = avg collector current calculated as the average of the High and low current, i.e.

\({I_{cc}} = \frac{{{I_{CCH}} + {I_{CCL}}}}{2}\)