Drive circuit for matrix displays

Abstract

Disclosed is a capacitive voltage divider drive circuit for electroluminent matrix displays comprised of, for example, thin film electroluminescent capacitance type elements. The drive circuit for each display element, which exhibits a relatively low capacitance, includes a relatively large series connected capacitor which couples a drive voltage thereacross upon the closure of a first switching element. Due to voltage divider action, a relatively greater portion of the drive voltage appears across and energizes the display element by exceeding its threshold voltage. Additionally, another relatively large capacitor is coupled in parallel with the display element upon the closure of a second switching element which, again due to voltage divider action, reduces the drive voltage thereacross below its energizing threshold level to deenergize it. The switching elements are comprised of semiconductor switch devices which are adapted to operate in timed relationship with a resonant AC drive voltage applied to the matrix. A plurality of row and column electrodes form the capacitive type display elements. Moreover, each row electrode in the matrix is connected to a respective first switching element while each column electrode is connected to a respective series capacitor as well as a respective parallel capacitor and second switching element.