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Variable Delay in Light Emitting Diodes

IP.com Disclosure Number: IPCOM000094298D
Original Publication Date: 1966-Aug-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Davidson, LA: AUTHOR [+2]

Abstract

The circuit allows variable delay and the performance of logic functions from the delay inherent in a light-emitting diode. The delay arises from the need to supply nonradiative current to satisfy the junction capacitance. When a pulse of current is supplied to a light-emitting diode, initially the majority of the current is used to charge the junction capacitance. The amount of current necessary to accomplish this, and hence the delay effect, can be varied by the initial biasing of the light emitting diode.

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Variable Delay in Light Emitting Diodes

The circuit allows variable delay and the performance of logic functions from the delay inherent in a light-emitting diode. The delay arises from the need to supply nonradiative current to satisfy the junction capacitance. When a pulse of current is supplied to a light-emitting diode, initially the majority of the current is used to charge the junction capacitance. The amount of current necessary to accomplish this, and hence the delay effect, can be varied by the initial biasing of the light emitting diode.

The circuit shows this effect in which a gallium arsenide light emitting diode having a junction capacitance at zero bias of 337. 8 pfs. is used as the light- emitting diode 1. The circuit has the advantage of complete electronic isolation of the load from the input signal. This is because only light 2 is passed from diode 1 to photodetector 3. The circuit is capable of obtaining variations of delay of up to 400 nanoseconds.

If gated logic is used, then for the condition of B positive and A fixed or preconditioned negative, an output at C does not occur. However, if A is zero, the specified output at C occurs. Hence, the And function is realized. One application of this phenomena is to use A as a control terminal on light-emitting diodes and thus have logical control of information inherent in input/ output equipment.

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