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 0.18 mu m 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 3.3V to 2.5V LDO-biased power supply.