CMOS ring VCO for UHF RFID readers

A complementary metal oxide semiconductor (CMOS) voltage controlled ring oscillator for ultra high frequency (UHF) radio frequency identification (RFID) readers has been realized and characterized. Fabricated in charter 0.35 μ m CMOS process, the total chip size is 0.47× 0.67 mm2. While excluding the pads, the core area is only 0.15× 0.2 mm2. At a supply voltage of 3.3 V, the measured power consumption is 66 mW including the output buffer for 50 Ω testing load. This proposed voltage-controlled ring oscillator exhibits a low phase noise of −116 dBc/Hz at 10 MHz offset from the center frequency of 922.5 MHz and a lower tuning gain through the use of coarse/fine frequency control.