Positionable element driving circuit

A positionable element driving circuit for supplying an AC driving voltage to a positionable element so as to alternatingly displace said positionable element, said driving circuit comprising:

• a displacing pattern signal source for supplying an AC displacing pattern signal;
• an amplifying means coupled to said displacing pattern signal source and supplied with said displacing pattern signal and having a gain for amplifying said displacing pattern signal by said gain;
• and a gain control means coupled to said amplifying means for controlling said gain of said amplifying means so as to make said gain correspond to a value which is inversely proportional to a gradient of a curve corresponding to said supplied voltage vs. a displaced position with respect to said positionable element, wherein said curve is defined by the relationship between said displaced position of said positionable element and the peak-to-peak voltage of said displacing pattern signal supplied directly to said positionable element.