i A PHYSICAL IMPLEMENTATION WITH CUSTOM LOW POWER ...

3.1.1 Static Power Consumption
Static power is the power dissipated when the gate or circuit is not switching. In other words, the
power consumed when the device is static or inactive can be called static power. The primary
source of static power comes from the leakage of current from the supply rail to ground through
various paths within the circuit. Hence, it has become conventional to refer static power as
leakage power.
Sub-threshold leakage has been one of the main sources of leakage in nanometer CMOS
technologies. Consider an NMOS transistor as an example. The sub-threshold leakage is due to
the current flow from the drain to source of the transistor, even when the gate voltage is set
below the threshold voltage of the transistor. This is because of the weak inversion layer that
exists in the channel at voltages close to the threshold voltage of the transistor. Sub-threshold
leakage has been shown to be the major leakage source in nanometer CMOS technologies. The
other sources of leakage include gate tunneling leakage and junction tunneling leakage. Gate
tunneling leakage is the current flow into or out of the gate terminal of a MOSFET. Gate
tunneling leakage has become an issue with nanometer CMOS technologies because of the
reduced gate oxide thickness. Junction leakage is the current flow from the drain or source
diffusion region to the body (substrate) terminal of a MOSFET. This leakage current is because
of the reverse biased junctions between the source/drain diffusion region and the substrate or the
well [6].
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