Browse Prior Art Database

LED Display With Inherent Memory

IP.com Disclosure Number: IPCOM000074409D
Original Publication Date: 1971-Apr-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Georgallis, GC: AUTHOR

Abstract

Reverse impedance recovery characteristics of LED's provide storage for regenerating an illuminated display matrix. Drawing A shows N rows of an X column LED display matrix. Stepping and access circuitry, Drawing B, continuously selects each LED in sequence via switches A through X and 1 through N shown in Drawing A. If a selected LED is to be illuminated, External Input is pulsed to turn on single-shot SS which activates transistor T, thus providing forward current to a selected LED. T remains on for the duration of the ON DRIVE interval indicated in timing chart, Drawing C. If the selected LED was on during the previous cycle of the stepping circuit, and it is selected again before the LED recovers its high-reverse impedance, reverse current (due to diode stored charge) will flow in sampling resistor R.

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LED Display With Inherent Memory

Reverse impedance recovery characteristics of LED's provide storage for regenerating an illuminated display matrix. Drawing A shows N rows of an X column LED display matrix. Stepping and access circuitry, Drawing B, continuously selects each LED in sequence via switches A through X and 1 through N shown in Drawing A. If a selected LED is to be illuminated, External Input is pulsed to turn on single-shot SS which activates transistor T, thus providing forward current to a selected LED. T remains on for the duration of the ON DRIVE interval indicated in timing chart, Drawing C. If the selected LED was on during the previous cycle of the stepping circuit, and it is selected again before the LED recovers its high-reverse impedance, reverse current (due to diode stored charge) will flow in sampling resistor R. This current flows through a circuit to ground, which is activated via the access circuitry by the sample pulse as shown in C. This current generates a pulse across R, which fires SS, turning on T and providing forward current to the LED during the ON DRIVE pulse. If the LED had not been illuminated during the previous time in which it was selected, no reverse current flows and the LED remains off unless the External Input were pulsed. If the LED had previously been on, and it is desired to turn it off, an INHIBIT signal provided by External Input is applied just prior to the ON DRIVE pulse.

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