High-Frequency Low-Noise Voltage-Controlled LC-Tank Oscillators Using a Tunable Inductor Technique

This paper describes 3-GHz and 7-GHz tunableinductance LC-tank voltage-controlled oscillators (VCOs) implemented in 0.18-μm CMOS technology. Unlike the traditional tuning method by a varactor, a tunable inductor is employed in the VCO by using a transformer to compensate for the energy loss. The VCO facilitates the tuning frequency and low noise of the output signals, together with a variable inductor which satisfies both criteria. The 3-GHz VCO using a symmetry transformer provides the tuning range of 2.85 to 3.12 GHz at 1-V supply. The power consumption is 4.8 mW while the measured phase noise is −126 dBc/Hz at 1-MHz offset from a 2.85-GHz carrier. A small-area stacked transformer is employed in the 7-GHz VCO, which achieves a tuning range of 6.59 to 7.02 GHz and measured phase noise of −114 dBc/Hz at 1-MHz offset from a 6.59-GHz carrier while consuming 9 mW from a 1.2-V supply. key words: LC VCO, tunable inductor, high Q, transformer