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Shared Drivers for ROLED Displays

IP.com Disclosure Number: IPCOM000088545D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Hung, R: AUTHOR [+2]

Abstract

In a rotating optical light-emitting diode (ROLED) display, a single line of light-emitting diodes (LEDs) is multiplexed by a rotating scanner into a complete display. Since the number of LEDs may be quite large in many applications, it may thus be desirable to reduce the number of drivers and wirings by using a sharing arrangement (i.e., a multiplexing scheme for the drivers). Such a shared arrangement is shown in the figure.

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Shared Drivers for ROLED Displays

In a rotating optical light-emitting diode (ROLED) display, a single line of light-emitting diodes (LEDs) is multiplexed by a rotating scanner into a complete display. Since the number of LEDs may be quite large in many applications, it may thus be desirable to reduce the number of drivers and wirings by using a sharing arrangement (i.e., a multiplexing scheme for the drivers). Such a shared arrangement is shown in the figure.

As depicted in the figure, there are N(G) groups of LEDs sharing a common cathode connection, each group consisting of N(L) LEDs. This requires N(G)+N(L) drivers, the number of LEDs being N = N(G)N(L), or (N(G)+N(L))/ N(G)N(L)) drivers per LED. The best ratio occurs for N(G) =N(L) (a "square" arrangement) in which case the required number of drivers is 2 Square Root N. For example, 50 drivers would be required to control 625 LEDs.

The duty cycle is 1/N(G). To maintain high brightness, it is necessary to choose a pulse current N(G) times the maximum average current of the LEDs. If this leads to an excessively high current, it will be necessary to depart from the optimum arrangement. As an example, diodes for which the pulse current is limited to 5 times the average current rating would require N(G) = 5. This still provides a substantial decrease in drive transistors, thus the 625 LEDs of the previous example could be driven by 125 small transistors (N(L)) plus 5 large ones (N(G)).

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