Differentially-Tuned VCO with Reduced Tuning Sensitivity and Flicker Noise Up-Conversion

Differential tuning in oscillators allows cancellation of common-mode bias noise and lower tuning sensitivity with respect to the most conventional single-ended tuning. However, the direct application of differential tuning increases the capacitor non-linearity and the flicker-induced phase noise. This paper analyzes quantitatively this phenomenon and proposes a novel configuration, which includes all the benefits of differential tuning with no penalty on phase noise. This circuit is fabricated in a 0.35-mgrm CMOS technology together with a single-end-tuned oscillator and both cover the 2.0–2.4 GHz frequency range. The measured 1/f3 phase noise at 10 kHz offset is –71 dBc/Hz, which outperforms the companion single-end tuning oscillator by 10 dB.