Sources of Power Dissipation

Abstract

This chapter presents various sources of power dissipation. At the outset, the difference between power and energy is explained, because most of the time when we say low power, we actually mean low energy. Various sources of power dissipations, both static and dynamic, are introduced first. The expression for short-circuit power dissipation, which is one of the dynamic power dissipations, is derived. Switching power dissipation, which occurs due to the charging and discharging of node capacitances, is introduced and the expression for switching power dissipation is derived. Switching activity for different types of gates is calculated. Switching activity for dynamic complementary metal–oxide–semiconductor (CMOS) circuits is also discussed. The expression for power dissipation due to charge sharing in dynamic CMOS circuits is obtained. Glitching power dissipation, which is another source of dynamic power dissipation, is introduced along with suitable approach to reduce it. Various sources of leakage power dissipations such as subthreshold leakage, gate leakage power dissipations are presented. Various mechanisms which affect the subthreshold leakage current are also highlighted.