Multiplexed display

Multiplexed displays are electronic display devices where the entire display is not driven at one time.

Instead, sub-units of the display (typically, rows or columns for a dot matrix display or individual characters for a character oriented display, occasionally individual display elements) are multiplexed, that is, driven one at a time, but the electronics and the persistence of vision combine to make the viewer believe the entire display is continuously active.

A multiplexed display has several advantages compared to a non-multiplexed display:

Multiplexed displays can be divided into two broad categories:

Most character-oriented displays (such as seven-segment displays, fourteen-segment displays, and sixteen-segment displays) display an entire character at one time. The various segments of each character are connected in a two-dimensional diode matrix and will only illuminate if both the "row" and "column" lines of the matrix are at the correct electrical potential. The light-emitting element normally takes the form of a light-emitting diode (LED) so electricity will only flow in one direction, keeping the individual "row" and "column" lines of the matrix electrically isolated from each other. For liquid crystal displays, the intersection of the row and column is not conductive at all.

In the example of the VCR display shown above, the illuminated elements are the plates of many individual triode vacuum tubes sharing the same vacuum enclosure. The grids of the triodes are arranged so that only one digit is illuminated at a time. All of the similar plates in all of the digits (for example, all of the lower-left plates in all of the digits) are connected in parallel. One by one, the microprocessor driving the display enables a digit by placing a positive voltage on that digit's grid and then placing a positive voltage on the appropriate plates. Electrons flow through that digit's grid and strike those plates that are at a positive potential.

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