Patent ID: 7667372

Claim:
An apparatus comprising two piezo-element driving units, each of the two piezo-element driving units comprising at least: an output connectable to a piezo-element, a voltage step-up module having a node wherein a voltage of said node is adapted to be an alternating voltage whose maximum is higher than a voltage of a power supply, a first switch to connect said output to said node for charging said piezo-element, at least one capacitor, and a second switch to connect said at least one capacitor to said output, said at least one capacitor being adapted to be disconnected from said node during said charging, and said second switch being adapted to transfer charge from said piezo-element to said at least one capacitor and back from said at least one capacitor to said piezo-element such that said at least one capacitor is disconnected from said voltage step-up module during the charge transfer in both directions; wherein the outputs of the two piezo-element driving units are in different phases.