Patent ID: 8854151

Claim:
An electrical resonant network whose resonance frequency, impedance or admittance can be controlled comprising; a) at least one first inductor coupled to at least one first capacitor that form a resonant circuit, b) at least one reactive component, c) at least one switch controlled by at least one ON/OFF coupling signal for coupling said reactive component to said first inductor and/or said first capacitor, wherein said reactive component is charged and discharged by the resonant circuit and said at least one ON/OFF coupling signal altering its state at least once within a resonant circuit period, d) a control circuit for generating said at least one ON/OFF coupling signal based on a pulse width modulation (PWM), and e) at least one quasi-zero crossing detector for synchronizing said pulse with modulation (PWM), wherein said quasi-zero crossing detector is responsive to a non-zero threshold level of a positive and negative voltage- or current half wave of the resonant circuit.