Extensional mode piezoelectric crystal resonator with split electrodes and transformer driving circuit

A piezoelectric resonator for use in a double-ended electrical transformer circuit, comprising:

• a single crystal piezoelectric body in the form of an elongated plate with an upper surface and a lower surface, the plate having a width and having a length along a transverse extensional mode of oscillation;
• and
• a first and a second set of substantially opposing electrode pairs disposed on the upper and lower surfaces of the plate in proximity to one another and defining a first and a second oscillating region therebetween, respectively, the electrodes of the opposing electrode pairs being substantially continuous along a width of the plate and separated by a gap running the width of the plate, the first and second regions being acoustically coupled;
• the opposing electrode pairs, when driven by electrical signals that are about 180.degree. out-of-phase from each other producing opposing electric fields in a thickness direction of the plate within each driving region, generating an even mode of transverse extensional oscillation in the plate with minimum extensional displacement in the gap;
• and
• the oscillating regions presenting substantially the same inductive impedance across their associated opposing electrode pairs.