Design and Optimization of Multipath Ring Oscillators

Multipath ring oscillators have been used to generate multiple clock phases and higher oscillation frequencies. This paper presents a modified linear analysis to find an accurate expression for the oscillation frequency and phase noise. The analysis shows that for the same power consumption, the number of phases can be increased without decreasing the oscillation frequency or degrading the phase noise. The expression further indicates factors that determine the oscillation frequency and shows that in principle, the maximum oscillation frequency can exceed that of a three-stage ring oscillator. The analytical results can be used to find the optimum coupling structure of the oscillator to achieve a desired operating frequency and phase noise performance.