This work presents a novel idea to dynamically control a differential ring oscillators biasing in order to improve the phase noise performance in the ultra low power domain. This proposed feedback system can be flexibly applied on any type of fully-differential ring oscillator with a tail current source. The following paper covers theoretical and simulative considerations to prove the feasibility of this idea. Finally measurements of a 180 nm standard CMOS integrated prototype system depict the implementability of this idea. A phase noise improvement of up to 35 dBc/Hz can be observed with an active control loop. Moreover, the tuning range of the implemented ring oscillator is extended by 434% in contrast to fixed bias operation. These values are measured at a minimum oscillation power consumption of 55 pW/Hz.