Circuit and method for frequency tuning of a vibrational energy harvester

A method of tuning an electric charge extraction circuit of a vibrational energy harvester having a mechanical resonator, the method comprising:

• varying, during a first phase, first and second parameters of the electric charge extraction circuit based on detected harvested power, each of the first and second parameters influencing an amount of damping of the mechanical resonator and at least the first parameter influencing a resonance frequency of the mechanical resonator, wherein the first and second parameters are varied during the first phase such that the amount of damping remains constant or varies by less than a first significant amount and the resonance frequency varies and reaches a final resonance frequency level;
• varying, during a second phase, at least the second parameter based on the detected harvested power such that the resonance frequency remains at the final level, or varies with respect to the final resonance frequency level by less than a second significant amount, and the amount of damping reaches a final damping level.