An N-path filter enhanced low phase noise ring VCO

A novel self-filtering scheme breaks the typical tradeoff between noise and power, enabling a ring oscillator to approach the phase noise performance of an LC oscillator. The prototype N-path filter enhanced voltage-controlled ring oscillator (NPFRVCO) achieves a measured phase noise of -110dBc/Hz at a 1MHz offset frequency for an oscillation frequency of 1.0GHz. The self-clocked N-path filter reduces the phase noise by 10dB and 28dB for 1.0GHz and 300MHz oscillation frequencies, respectively. Implemented in 65nm CMOS, the NPFRVCO occupies a die area of 0.015 mm² and consumes 4.7mW from 1.2V power supply when operating at 1.0GHz. The NPFRVCO has a measured frequency tuning range from 300MHz to 1.6GHz and achieves a FoM of 163dB at 1MHz offset.