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Subthreshold leakage
From Wikipedia, the free encyclopedia
Subthreshold leakage or subthreshold conduction is the current that flows between the source and drain of a MOSFET when the transistor is in the weak-inversion region.
In digital circuits, subthreshold conduction is generally viewed as a parasitic leakage in a state that would ideally have no current. In micropower analog circuits, on the other hand, weak inversion is an efficient operating region, and subthreshold conduction is a normal transistor property around which circuit functions are designed.
In the past, the subthreshold leakage of transistors has been very small, but as transistors have been scaled down, subthreshold leakage can compose nearly 50% of total power consumption. The reason for this is that the supply voltage has continually scaled down to reduce the dynamic power consumption of integrated circuits (the power that is consumed when the transistor is switching from an on-state to an off-state) which depends on the square of the supply voltage. As the supply voltage is scaled down, to maintain performance, the threshold voltage has to be reduced in the same proportion. As threshold voltages are reduced, subthreshold leakage rises exponentially.
