A wideband VCO with constant tuning-gain and uniform sub-band interval for single-chip UHF RFID reader

A novel VCO with constant tuning-gain and uniform sub-band interval is presented in this paper for single-chip UHF RFID reader application. An optimized calculation method is proposed to attain the accurate capacitor ratio for digital-controlled capacitor array units. The resistor-biased switched-capacitor structure is used to achieve large frequency range and optimized phase noise performance. The circuit is realized in 0.18μm CMOS process and the simulation results show that the VCO features a tuning-gain from 46.8 to 50.7MHz/V with ±4% variation and a sub-band interval from 47 to 49 MHz with ±2% variation for frequencies from 3.23 to 4.03GHz and phase noise of -128.5dBc/Hz at 1MHz offset from 3.6GHz carrier. The whole circuit consumes 5.9mA from a 3.3 V to 2.5 V LDO-biased power supply.