An ultra-low power ring oscillator for passive UHF RFID transponders

This paper presents a new two-stage CMOS voltage-controlled ring oscillator (VCO) designed for passive UHF RFID transponders. The goal is to explore the design space for the lowest possible power dissipation. A nano-power VCO capable of functioning as a local oscillator for the transponders is obtained by biasing the delay cells to operate in weak inversion region. Further power reduction is achieved by transistor sizing. Designed in a 90 nm CMOS technology, the proposed circuit generates oscillation signals at 5.12 MHz and consumes only 24 nW with 0.3 V power supply.