Area, Speed and Cost were used to be the main concerns in the VLSI industry and Power consumption was the secondary consideration. But, nowadays, Power is given equal importance as area and speed. The increasing demand for mobile electronic devices which require complex functionality and high speed has increased the requirement for power efficient VLSI circuits. Since, a large number of transistors are being packed onto a single chip, the increase in operating frequency and processing capacity results in increased power dissipation. Power dissipation plays an important role in VLSI circuits since it not only causes overheating which reduces chip life but also makes it difficult to use devices in a portable environment [1]. Also, it results in waste of energy in form of heat which is obviously a major concern nowadays.

Transistor Gating Drain Gating Power Gating Low Power Source Gating Power Dissipation Source of Power Dissipation.