Differential ring oscillator based voltage control oscillator for readerless RFID transponder

Designing a compact, power efficient voltage controlled oscillator (VCO) for high frequency phase lock loop (PLL) in modern wireless communication system is decisively a challenging task. Inappropriately designed VCOs for battery-powered radio frequency identification (RFID) transponder cause huge degradation of overall system. The proposed work presents a low power 2.45 GHz VCO developed for active readerless transponder compatible with IEEE 802.11b protocol. A 3-stage, single delay path, differential ring oscillator based architecture has been adopted for the ease of integration and implementation of the circuit in small die area. 0.18μm CMOS process is used for designing the proposed VCO. Simulated results showed that the proposed VCO would work in the tuning range of 2.4GHz-2.5GHz with 1.8V supply. Thus, the proposed VCO will be a key component for readerless RFID transponder.