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A Wide-Tunning-Range Low-Phase-Noise Colpitts Oscillator with Variable Capacitive Feedback

In this paper, we propose a technique to extend the tuning range (TR) of Colpitts complementary metal-oxide semiconductor (CMOS) voltage-controlled oscillators (VCOs). To achieve a wide tuning range, we use variable capacitive feedback to extend the tuning range while achieving lower phase noise (PN) than that of the conventional Colpitts VCOs. In addition, the structure benefits from the dynamic forward-body self-biased technique to reduce the power consumption and facilitate the start-up condition. As a proof-of-concept, a 28-GHz Colpitts oscillator, which is suitable for 5G wireless applications, is designed and laid out in a 65-nm CMOS process. Post-layout simulations in conjunction with electromagnetic (EM) simulations confirm the improved performance of the proposed technique. Based on the simulation results, the VC O achieves a PN of −115.7 dBc/Hz at 10-MHz offset, and TR of ∼34.5% resulting in a figure of merit incorporating the tuning range (FOMt) of −189 dBc/Hz. The circuit consumes 4.3 mW from a 1-V supply and excluding the pads occupies a 0.12 mm2 of silicon area.