A Low-phase-noise 1-GHz LC VCO Differentially Tuned by Switched Step Capacitors

This paper proposes a novel 1-GHz LC oscillator differentially tuned by switched step capacitors, which is implemented in a 0.25mum 1P5M CMOS process. A period calculation technique (PCT) is adopted to analyze the differential tuning characteristic of switched step capacitors. Due to the symmetric oscillation waveforms, the differentially tuned LC VCO has 7 dB phase noise reduction in the 1/f
³
region compared to the single-ended tuned topology, and 23.6dB CMRR. It achieves phase noise -83 dBc/Hz, -107 dBc/Hz and -130 dBc/Hz respectively at 10-kHz, 100-kHz and 1-MHz offsets, while dissipating 3.3 mA current at 2.6 V power supply. Chip size is 0.82 mm times 0.84 mm