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This paper presents a 0.6-V quadrature voltage-controlled oscillator (QVCO) with enhanced swing for low power supply applications. The QVCO comprises a novel capacitive coupling technique that is employed not only for quadrature signal coupling, but also for phase noise reduction. As a result, the proposed QVCO can even achieve 4.6 dB lower phase noise than its single-phase counterpart at 3-MHz offset. Optimized capacitive coupling combined with source inductive enhance-swing technique enables low power and low phase noise simultaneously. The QVCO achieves a measured phase noise of -132.2 dBc/Hz @ 3-MHz offset with a center frequency of 5.6 GHz and consumes 4.2 mW from a 0.6-V supply. This performance corresponds to a figure-of-merit (FoM) of 191.4 dB. Due to the intrinsic phase shift in the proposed quadrature-coupling path, the problem associated with ±90° phase ambiguity between the quadrature outputs has been avoided. The QVCO RFIC is implemented in a 0.13 μm CMOS process with core area of 0.6 × 0.8 mm2.