Low Phase-Noise and Wide Tuning-Range CMOS Differential VCO for Frequency ?S Modulator

In this paper, a novel low phase-noise and wide tuning-range CMOS differential Voltage-Controlled Oscillator (VCO) for a frequency ΔΣ modulator (FDSM) is presented. The VCO which converts an analog input voltage to phase information is based on a differential ring oscillator with modified symmetric load and a positive feedback in the differential delay cells, combined with a new bias circuit. The proposed VCO with two stages operating at a low power supply voltage of 0.6V can achieve low power consumption of 212uW, and wide tuning-range by increasing the operating frequency range by about 22%. The phase noise is -132dBc/Hz at 600KHz offset from the centre frequency of 480MHz. The new VCO has a good linearity reducing harmonic distortion in the ΔΣ modulator. The circuits are designed using a 65nm CMOS process.