Star-Delta Connection Three-Stage Millimeter Wave Band LC Ring Oscillator

In this paper, a new topology is proposed for a three-stage LC ring oscillator. First, it is shown that the conventional ring oscillator can be represented as a configuration of a star connection of inductors. Next, in the proposed topology, the star connection is replaced with a star-delta connection to increase the inductance value for a given oscillation frequency. This is desirable in millimeter-wave band frequencies, where the inductance value is very small and severely affected by parasitic and may entail limitations in foundry design kits. By using the delta connection of the inductors, a higher oscillation frequency is achieved for a given inductance. Analytic equations are presented to calculate the oscillation condition and frequency of oscillation in the proposed topology. Moreover, the proposed structure has a better phase noise performance at higher frequencies in comparison to conventional topology. The advantages of the proposed topology are examined by simulations using TSMC 0.18 um RF-CMOS technology. Simulations and analysis results show a 38.36% increase of oscillation frequency in the proposed topology compared to the conventional one with the same components and similar conditions.