Simulation And Design Of Phase Noise Of Oscillator With Nonlinear Excitation

In practical applications,nonlinear excitation will change the measurement results of the phase noise of oscillator.It is of necessity to consider nonlinear factors in the design of oscillator.This paper analyzes and designs the phase noise of oscillator with nonlinear excitation.Three different types of nonlinear analysis methods are simulated,deduced and measured.The influences of these methods on oscillator's phase noise are analyzed.The main work of this paper is as follows:1)In this paper,a 100 MHz oscillator based on colpitts circuit is designed,without any extra nonlinear excitation.Through ADS simulation,its phase noise result can be obtained,which turns out to meet the requirement of this paper.The phase noise result is used for comparison with the following analysis results of oscillator with nonlinear excitation.2)The existence of noise in oscillators is unavoidable.The first kind of nonlinear excitation is nonlinear noise source model added in oscillating circuit.The noise model is a nonlinear noise source model based on the root mean square algorithm(RMS),and the order of magnitude of RMS value X of this noise source is nV.This model is added to the original 100 MHz oscillation circuit.Compared the phase noise result of this combined circuit with the original result,the deterioration of phase noise is significant.While X =300nV,the near end of phase noise is deteriorated by 25 dB,and the mid end deteriorates by 43 dB.It can be concluded that this noise model will lead to deterioration of phase noise.3)Voltage controlled frequency modulation technology is a commonly used nowadays.The second method draws on the principle of voltage-controlled frequency modulation.A nonlinear circuit module is composed of input voltage and a varactor,and is connected with resonators in series.With changes in input voltage,the frequency of oscillator varies as well.Compared with the original data,the simulation of the phase noise curve deterioration by 13 dB when input voltage is 24 V.It is proved that the nonlinear excitation based on the voltage controlled frequency modulation will cause phase noise's deterioration.4)The last nonlinear analyze is based on the amplitude frequency(AM)characteristics of resonator,namely,the relation between the oscillation frequency offset and the exciting current.By deriving mathematical relation between frequency offset and current,a nonlinear complicated relation is exhibited.In this way,the current flowing through the resonator can be regarded as a nonlinear excitation,which would affect the resonator only.In this paper,the amplitude frequency characteristics of fifth harmonic and first harmonic100 MHz resonators are measured.It is found that the nonlinear amplitude frequency characteristics exist in the measured resonator.Meanwhile,by measuring three groups of 100 MHz resonators,it is found that the flicker noise will vary with the change of exciting current,namely,the amplitude frequency characteristics will affect the flicker noise.It turns out that all the three nonlinear analysis methods introduced will influence oscillator's phase noise,and the first two nonlinear excitations will lead to deterioration of phase noise.