Passive multiplexing of printed electroluminescent displays

— A method is required for creating a graphics display, or pixel array, from printed electroluminescent (PEL) display technology and driving it efficiently and cost effectively. The display is made up of a matrix of capacitive light-emitting display elements which are to be driven by a passive multiplexing method. A four-level drive system is required in order to produce the best possible contrast ratio on the display. A four-level drive system is costly to implement at the high voltages at which PEL displays operate, but a system is presented here which is able to make a significant reduction in the amount of electronics required to control the display. By selectively switching the output from a fly-back power supply to different parts of the matrix display, the optimum voltages can be obtained across all segments from a single high-voltage power supply. This provides potential for using passive-matrix PEL displays in a wide variety of applications, as well as having possible applications for other display technologies such as PDLCs (see demonstration in Fig. 1).