Novel six-phase ring voltage controlled oscillator with wide frequency tuning range

This paper presents more compatible three-stage inverter-based ring voltage controlled oscillators (VCOs) by modifying the current-starved delay cell to oscillate with high tuning range. Unlike some ring structures in which extra transistors are used as current boosting to enhance the frequency tuning range, no extra elements are used in the proposed three-stage VCOs for increasing the tuning range. Besides, a new method is introduced to couple two proposed ring VCOs for designing a six-phase ring VCO. The coupling method can be generalized to some other ring VCOs to generate multiphase signals. The proposed circuits have wide frequency tuning ranges and show good noise performances. The proposed six-phase VCO can oscillate from 1.62 GHz to 3.45 GHz, which illustrates 72.2% tuning range. The phase noise of the proposed VCO is -97.5 dBc/Hz at 1 MHz offset frequency. The circuit figure of merit is -181.5 dBc/Hz. The post-layout simulation results of the proposed six-phase VCO are provided based on the TSMC 0.18 mu m CMOS process. A novel six-phase ring voltage controlled oscillator has been realized by capacitively coupling of two identical single-ended three-stage ring VCOs. The designed circuit oscillates at 2.95 GHz with wide tuning range of 72.2% and phase noise of -97.5 dBc/Hz at 1 MHz offset frequency.image