The Research And Application Of CMOS Ring VCO

There are ring VCO and the LC VCO in the CMOS integrated circuit.The Q value of LC VCO is high and it has strong noise suppression ability.However,the large chip area occupied by inductance is the biggest disadvantage.The ring VCO is made of MOS transistor and it has the advantages of easy integration,wide tuning range and small chip area.But phase noise is higher than LC VCO about 20?40 dBc/Hz@1MHz.The poor performance of phase noise is a fatal shortcoming and severely limits its application.At present,the design of VCO with low phase noise becomes an urgent problem,so the purpose of this paper is to design a loop VCO which phase noise performance equivalent to the LC VCO.The main contents of this paper can be summarized as follows:(1)In this paper,the working principle of voltage controlled oscillator is discussed.Several classical structures are analyzed and compared.The contribution of the positive feedback introduced in the differential delay cell in improving the frequency of VCO and improving the phase noise performance is analyzed.The frequency modulation mode of the ring oscillator is analyzed.The compromise between VCO power consumption,phase noise,frequency,output swing,and linearity are discussed.These analyses provide a basis for the design of the VCO in the choice of the differential structure,the way of frequency regulation,the compromise between the various indicators and so on.(2)The noise mechanism of voltage controlled oscillator is discussed.Firstly,the contribution of the signal path and control path to the phase noise is discussed.Secondly,We have deduced the two common models of phase noise:Lesson model and Hajimiri model,and the advantages and disadvantages of the two models are analyzed.Finally,several methods to reduce the phase noise are given.(3)A ring voltage controlled oscillator with tunable frequency range of 2?4GHz is designed.For the poor noise suppression ability of the ring voltage controlled oscillator,a waveform adjustment module is designed to charge and discharge for the output node of the delay unit in the process of electrical level switching.The switching speed of the delay unit is improved,then the amplitude of the waveform is improved,and the symmetry of the rise and fall time of the waveform is improved.Finally,the phase noise of the ring VCO is reduced.This is the most innovative part of this paper and the proposed noise reduction measures are based on the Lesson model and Hajimiri model.Finally,the layout design rules and skill are discussed,and a complete design layout of VCO is given.(4)This paper briefly introduces an areas of application:voltage-controlled oscillator clock circuit.The design of each circuit module are given.The performance of the VCO is verified.