A 1.22/6.7 ppm/°C VCO with frequency-drifting compensator in 60 nm CMOS

This paper presents a low-temperature coefficient VCO with a proposed frequency-drifting compensator. The compensator inside the VCO core can work both in burst-mode and continuous-mode operations. With its integration in the frequency synthesizer, no impact on spur and phase noise degradation is observed. A fractional-N synthesizer with this compensator is fabricated in a 60nm CMOS technology with core area of 0.31 mm². In the burst-mode operation, the measured VCO temperature coefficient is 1.22ppm/°C over -20 °C~80°C as the VCO operates at 4.2GHz. In the continuous-mode operation, the measured temperature coefficient is improved from -35ppm/°C to 6.7ppm/°C at 4.2GHz over -20°C ~50°C. The PLL phase noise at 3MHz offset is -137.4dBc/Hz and almost unaffected.