Optimization of the Phase Noise of LC VCO in UHF RFID Reader

A low phase noise LC voltage controlled oscillator for UHF radio frequency identification reader is presented in this paper. Symmetrical LC resonators and a low-dropout-regulator are used to suppress the noise from tail current and power supply, respectively. 3-bit switched-capacitor array for coarse tuning followed by MOS varactors for fine tuning to ensure a Low voltage controlled oscillator gain (<48 MHz/V). The circuit is implemented in IBM 0.18 mum CMOS process, and the measured phase noise is -136.25 dBc/Hz at 1 MHz offset from the carrier while drawing 4.5 mA from a 3.3 V supply.