Although voltage controlled oscillators (VCOs) are widely used, their design is still quite difficult, since it involves many trade-offs regarding the range of frequency of oscillation attainable, area, power and noise. The development of efficient and reliable simple models for VCOs is therefore of capital importance for the automatic design of these circuits. As far as ring voltage controlled oscillators are concerned several models have been proposed, based on the evaluation of the delay introduce by each stage comprising the oscillator. However, the simple models turn out to be quite inaccurate for oscillators comprising a small number of stages. Such inaccuracy is particularly restrictive when high frequency signals are to be generated. In this paper a general, simple and accurate model is proposed to overcome the mentioned limitations
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