18-GHz band low-power LC VCO IC using LC bias circuit in 56-nm SOI CMOS

This paper presents a novel 18-GHz band 0.5 V Class-C pMOSFET LC-VCO IC. The LC-VCO IC consists of an oscillator core circuit with a cross-coupled pMOSFETs and an LC bias circuit, an amplitude feedback circuit for realizing Class-C operation and buffer amplifiers. The VCO IC starts to oscillate in Class AB mode and enters Class C mode in the steady-state by changing the gate bias voltage. Since the LC bias circuit increases the current amplitude of the VCO and Class-C operation prevents the pMOSFETs from entering into the deep-triode region, the novel VCO circuit topology is effective in improving the phase noise. The low-power LC biased VCO IC is designed, fabricated and fully evaluated on-wafer in 56-nm SOI CMOS technology. The fabricated VCO IC has exhibited a measured phase noise of -117.6 dBc/Hz at 5 MHz offset from the 18.88 GHz carrier frequency with a supply voltage of only 0.5-V. The power consumption of VCO core is 2.56 mW and that of the feedback loop is only 0.046 mW.