Multipath Ring Oscillator Research Articles

The Oscillation Frequency of CML-based Multipath Ring Oscillators

A novel phase interpolator (PI) based linear model of multipath ring oscillator (MPRO) is described in this paper. By modeling each delay cell as an ideal summer followed by a single pole RC filter, the oscillation frequency is derived for a 4-stage differential MPRO. It is analytically proved that the oscillation frequency increases with the growth of the forwarding factor α, which is also confirmed quantitatively through simulation. Based on the proposed model, it is shown that the power to frequency ratio keeps constant as the speed increases. Running at the same speed, a 4-stage MPRO can outperform the corresponding single-stage ring oscillator (SPRO) with 27% power saving, making MPRO with a large forwarding factor α an attractive option for lower power applications.

Analysis and Design of Superharmonic Injection-Locked Multipath Ring Oscillators

Frequency dividers can be modeled as superharmonic injection-locked oscillators. We propose a general model for ring-oscillator based dividers. Theoretically, the maximum division frequency of a frequency divider can be decoupled from the number of phases at its output when multipath coupling of ring oscillators is used. Accurate expressions for the locking range are derived that are used to find the optimum structure to maximize the division frequency. The results of the model are incorporated into a design procedure that can rapidly explore various coupling and sizing of the multipath structure. A design of a divider chain for a 48-Gb/s serializing transmitter is used as a demonstration.

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.

Tuning Characteristics of Multipath Ring Oscillators

A multipath ring oscillator is composed of i chain of inverters, the outputs of which are weighted and combined to provide the feedback signal. Multipath oscillators may be operated in two basic modes, viz, the mux mode and quadrature controlled mode. In the mux mode the frequency of oscillation is controlled by varying the effective number of inverter stages while the quadrature mode utilizes injected quadrature currents to control the frequency.The performance characteristics of multipath ring oscillators are presented. Experimental results on tuning characteristics of several two-path and three path VCOs are presented. Results are also given for a PLL using phase frequency detector and charge pump, and for a crystal controlled VCO using a ring.