A low phase noise and wide-band VCO for UHF RFID reader

Based on the 0.18 μm CMOS process, a low phase noise voltage-controlled oscillator (VCO) with wide-band for UHF RFID reader was presented. The VCO was supplied by a fully integrated low-output-noise and high power supply rejection ratio (PSRR) low-dropout linear regulator (LDO). To widen the output frequency range, a 4 bit resistor-biased switch capacitor array (SCA) was used. The resistor-biased switch capacitor reduced losses introduced by the parasitic diodes and improved the VCO phase noise performance. Measurement results show that: the whole circuit consumes a current of about 4.8 mA with 2.5 V power supply of LDO. The output frequency of VCO could change from 3.12 GHz to 4.21 GHz (increase by 30.5%). The circuit achieves a phase noise of -109.9 dBc/Hz at 200 kHz offset and -129 dBc/Hz at 1 MHz offset with the 3.6 GHz center frequency.