Radiation hardened level shifter for sub to superthreshold voltage translation

For ultra low power applications, improved energy efficiency can be achieved by operating non-critical portions of the logic in the subthreshold region (V_DD <; V_TH) while performance-critical sections are maintained in the superthreshold region (V_DD >; V_TH). Signal interfacing from subthreshold to superthreshold levels is a significant challenge and requires a robust level shifter that operates across an extreme input-to-output voltage range. Beyond the challenges of translating signals between such disparate voltages, another concern is the increased sensitivity to radiation that results from the weakened drivers in the traditional level shifter feedback structure. This paper presents a novel rad-hard ultra-low-power level shifter that 1) is Single Event Upset (SEU) immune over a wide range of supply voltages due to a Dual Interlocked Storage Cell (DICE) feedback and 2) is optimized for translating signals from sub to superthreshold levels. Radiation hardness of the proposed design is captured as Q_crit - the amount of radiation-induced charge required to flip the output unintentionally. The proposed design provides SEU resilience at subthreshold voltage (0.45V) with 12x improvement in Q_crit values as simulated using 250 nm CMOS TSMC technology models.