Sound generator including an ultrasound unit, display device including the sound generator, and method of driving display device

A sound generator for a display device, comprising:

• a first vibration generation unit having a first electrode, a second electrode, and a first vibration layer between the first electrode and the second electrode;
• and
• a second vibration generation unit having a third electrode, a fourth electrode, and a second vibration layer between the third electrode and the fourth electrode,
• wherein the first vibration generation unit is configured to contract and expand the first sub-vibration layer based on a first driving voltage applied to the first electrode and a second driving voltage applied to the second electrode,
• wherein the second vibration generation unit is configured to contract and expand the second sub-vibration layer based on a third driving voltage applied to the third electrode and a fourth driving voltage applied to the fourth electrode,
• wherein the first vibration generation unit is a sound output unit configured to generate an audible sound, and
• wherein the second vibration generation unit is an ultrasonic wave output unit configured to generate an ultrasonic wave.