Ultra Low Voltage Level Shifters to Interface Sub and Super Threshold Reconfigurable Logic Cells

Ultra-low power consumption often comes at the price of reduced performance for energy conscious electronics - particularly reconfigurable circuits. Operating devices at ultra-low voltage levels provides the lowest energy per operation, but can penalize the frequency of operation by several orders of magnitude. A more optimized approach is to segregate the logic based on performance requirements and use multiple voltage levels to supply separate voltage islands in an integrated circuit. The concept can be extended such that the low performance circuits can be supplied with a voltage below the threshold voltage of the transistor (i.e. subthreshold logic), however no analysis has been completed to date with regards to the performance and operation of the level shifters required for communication between voltage islands of such disparate levels. This paper compares a variety of existing level shifters as well as several proposed level shifters in the context of up-converting subthreshold signals to superthreshold levels.