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This paper presents a scalable low voltage CMOS folded-cascode quadrature voltage controlled oscillator (QVCO) design for radio-frequency (RF) applications using the TSMC 0.18 μm 6M1P CMOS process technology. The simulated startup behavior of this proposed QVCO topology indicates that, the QVCO is free from bi-modal oscillation (frequency ambiguity). The QVCO provided extended voltage swing with the supply voltage scalable in the range of 1.8 V to 0.75 V. The QVCO operates in the frequency range of 4 GHz to 3 GHz (corresponding to supply voltage scaling in the range of 1.8 V to 0.75 V) with around 11.7% tuning range and low quadrature error. The QVCO had a power consumption under 10 mW within the specified supply voltage scaling range. Phase noise simulations using the Monte Carlo analysis provide an approximate phase noise estimate of ≈ -150 dBc/Hz at an offset of 600 KHz from the center frequency (@3.7 GHz) for operation using the 1.8 V supply voltage, using moderate inductor-Q values. Monte Carlo simulations were also carried out to determine the effects of the process, voltage and temperature variations.

This study presents a new wide-tunable, area-efficient and low-phase noise quadrature voltage-controlled oscillator(QVCO). Initially, a modified Colpitts voltage-controlled oscillator (VCO) is proposed in which all transistors are cross-connected in a self-biased scheme to increase negative resistance and facilitate the startup condition. Besides, instead of a passive inductor, a modified tunable active inducer (AI) is used in the proposed Colpitts VCO. Then a new AI-based QVCO is presented by the in-phase anti-phase coupling of two identical Colpitts VCOs. The core VCOs are coupled by the current source transistors of the AI and in this way, no extra coupling devices are used. The proposed AI-based QVCO is designed and simulated in TSMC $0.18\mu \mathrm{\text{m}}$ CMOS technology by Cadence. Post-layout simulation results show that the proposed QVCO occupies only $0.024{\mathrm{\text{mm}}}^2$ of chip area, and has a phase noise of −106.6dBc/Hz at 1MHz offset from the 0.7GHz oscillation frequency. A wide frequency tuning range (FTR) of 68% (i.e., 0.68–1.4GHz) is achieved by adjusting the tuning voltage of the active inductor (AI), and the total power consumption is 7.2mW. Coarse and fine frequency tuning of the QVCO is available by changing the emulated inductors and varactors, respectively, that gives $K_{\mathrm{\text{vco}}}$ of 1100 and 34MHz/V, respectively.