Low-noise voltage-controlled oscillators using enhanced LC-tanks

摘要

Frequency synthesizers used in modern telecommunication systems,nsuch as cellular telephones, need to have very low phase noise.nTherefore, in the design of high performance frequency synthesizersnusing Phase Locked Loops (PLL), the Voltage-Controlled Oscillator (VCO)nhas become a key issue. The trend towards monolithic Integration posesnsome major challenges. This paper discusses the phase noise aspects ofnLC-tuned oscillators. A general formula is developed, based on thenconcepts of effective resistance and capacitance. The formula alsonapplies for oscillators using active inductors. From these results thenimportance of an inductor with very low series resistance is apparent.nTo circumvent the technological limits given by an Inductor's seriesnresistance, a presented enhanced LC-tank can be used to make a trade-offnbetween noise and power