| An integrated voltage-controlled oscillator (VCO) is an essential building block in modern communication systems, and low phase noise is a critical parameter for good system performance. Traditional CMOS VCO designs using LC tank circuits achieve their lowest phase noise performance by using the minimum gate length permitted by the technology. Most designs produce a reliable and high Q LC tank circuit, but the variation of MOSFET noise with device size is not taken into account. This research considers how the sizes of the MOSFETs affect the phase noise of the VCO. In addition, the relationships between the power consumption, the output signal level, and the properties of the LC tank circuit are characterized. Based on these analyses, a design methodology for lowest phase noise in LC tuned CMOS voltage-controlled oscillators is developed. Six VCOs with the same tank circuit, but different sizes of the MOSFETs, were simulated, laid out, and fabricated using AMIC5N (0.5μm) technology. A 5 GHz VCO with optimum gate length has been simulated, laid out, and fabricated using TIs' 0.15μm technology. The measurement results of the 1 GHz VCOs have verified the developed design methodology. |
