Analysis of Phase Noise and Jitter in Ring Oscillators

Voltage controlled oscillators (VCOs) have gain paramount importance in frequency modulation (FM) and pulse modulation (PM) circuits, phase locked loops (PLLs), function generators, frequency synthesizers etc. which are vital for communication circuits. CMOS based ring oscillators have tuning range, tuning gain and phase noise as the important characteristics. The most difficult task is that variation of phase due to stochastic perturbations. Phase noise has been the designer’s primary concerned. The effect of oscillator’s noise is one of the most insightful issues in the designing of modern RF telecommunication systems. A low phase noise with minimum power dissipation is rapidly preferred criteria for the design of voltage controlled ring oscillators (VCROs). A very simple and precise analysis of different phase noise models of ring VCOs and their causes is analyzed in this paper. For each case, the flicker noise and the white noise component of phase noise and jitter are considered which limits the signal. The important elements that determine the phase noise in VCOs are the transistor's flicker noise ( noise), the output power level, and the quality factor (Q). A synchronized relationship among the effective noise components in the oscillatory circuits leads to good agreement for new design insights and also improves the performance. Keywords: Ring Oscillators, Voltage Controlled Oscillator, Voltage Controlled Ring Oscillator, Phase noise, jitter