In this work we propose a self-adaptive clock based on a ring oscillator as the solution for the increasing uncertainty in the critical path delay. This increase in uncertainty forces to add more safety margins to the clock period which produces a circuit performance downgrade. We evaluate three self-adaptive clock systems: free running ring oscillator, infinite impulse response filter controlled RO and TEAtime controlled ring oscillator. The safety margin reduction of the three alternatives is investigated under different clock distribution delay conditions, dynamic variation frequencies and the presence of mismatch between the ring oscillator and the critical paths and the delay sensors.