Design of a 1 V low power 900 MHz QVCO

This paper describes the design of a 1 V, 900 MHz quadrature voltage controlled oscillator (QVCO) implemented in 0.18μm CMOS technology. The VCO can be tuned from 825 to 975 MHz, which corresponds to a tuning range of 16.6%, consuming only 3.5 mW of power for quadrature signal outputs. The phase noise of the VCO is -136 dBc/Hz at 3 MHz offset from 900 MHz. The VCO features discrete tuning using switched capacitors with a K_vco of 50 MHz/V which makes it very suitable for using in a PLL. Challenges with low voltage implementation of the VCO and modifications required both at device and circuit level are discussed in detail. Novel design of the VCO has also ensured very low supply sensitivity of the output frequency (K_VDD = 6 MHz/V) despite low supply voltage.