A low-power low-noise VCO with nearly constant Kvco for UHF RFID transceivers

In this paper a low-power low phase noise VCO with nearly constant K_VCO for UHF RFID transceivers is presented. To achieve a wide tuning range while maintaining a low K_VCO and phase noise, a 6 bit digital controlled capacitor array is used. To achieve a nearly constant K_VCO in a wide tuning range, an improved 3 bit digital controlled varactor array is proposed. With the TSMC 0.18 μ m 1p6m RF CMOS process, the simulated K_VCO is less than 30MHz/V in a 20% tuning range. The phase noise is lower than -127 dBc/Hz @1MHz offset at 1.8 GHz. At the same time, the K_VCO variation is ±2% in a single sub-band and the overall variation is lower than ±7% within the operation frequency of interest. The VCO consumes 3.5 mA current under 1.8 V supply voltage.