Multi-ring coupled ring oscillator with improved phase noise

Abstract

The disclosure of the present application presents a multiple-ring coupled ring oscillator design that employs multiple-ring coupling to achieve improved phase noise by minimizing noise injection from tail current and adjacent rings, while providing additional output phases for multiphase signal generation. In one non-limiting exemplary prototype embodiment, a 1.5 GHz triple-ring coupled ring oscillator achieved measured phase noise of −110.5 dBc/Hz at 1 MHz offset, demonstrating phase noise reduction of 7 dB compared with its single-ring oscillator counterpart. The MROs couple multiple rings with proper phase shifting to achieve improved phase noise. Common source coupling benefits from tail current noise reduction, and introducing phase delays in the coupling paths minimizes noise coupling from the adjacent cores. The overall effect leads to improved phase noise performance as demonstrated in quadrature voltage controlled VCO designs. The concept is applied to ring oscillator designs and, as stated previously, demonstrates a triple-ring coupled ring oscillator with phase noise improvement. The design of the present application also triples the number of output phases compared to its single ring oscillator counterpart. The application of injection-locked PLL by using proposed multiple ring coupled ring oscillator achieves the same low phase noise as traditional IL-PLL does while lowering the reference spur at auxiliary ring's output. In another non-limiting exemplary embodiment, the proposed IL-PLL consumes 13.5 mW of power, while achieving in-band phase noise of −120.97 dBc/Hz at 1 MHz offset at 1.1 GHz output frequency.