A fully integrable hybrid power management unit for passive UHF RFID

Abstract

This paper presents a fully integrable hybrid power management unit (HPMU) realized in the 130 nm generic CMOS (complementary metal-oxide-semiconductor) process from GlobalFoundries to increase the performance of RFID tags—especially those with passively powered sensors—by intelligently managing harvested power. The HPMU strategically takes advantage of the excess harvested power beyond the operational requirements of a tag and stores this energy externally. Through intelligent power routing, this stored energy is used to sustain the supply voltage of tag circuitry during brownouts, cold starts, and for reading ranges where harvested power is inadequate to power tag logic circuits but the tag distance to an interrogating antenna is close enough to expect a backscattered response to be received by an RFID reader. This approach can reduce cold start-up time, mitigate consequences of brownouts and, effectively, extend the operational range and the responsiveness of tags—especially those with passively powered sensors. In addition, the HPMU switches off when the harvested power, indicative of a weak interrogating signal, is too low to conserve stored power. The entire HPMU has been optimized for low power consumption, which not only reduces the power overhead that HPMU introduces but also ensures that as much power as possible is siphoned and stored rather than dissipated in the power management circuitry. In off state, the HPMU consumes only around 10 nA from the external storage element and during charge storage mode of operation, the HPMU has a peak conversion efficiency of approximately 65%.