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Temperature Compensation Circuit for Edge Emitting LEDs

IP.com Disclosure Number: IPCOM000108396D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 1 page(s) / 39K

Publishing Venue

IBM

Related People

Strayer, DE: AUTHOR [+2]

Abstract

Edge-emitting LEDs (ELEDs) offer better coupling of light into fiber than surface-emitting LEDs (SLEDs). However, the average optical power of the ELED exhibits a much stronger dependence on temperature and may vary by as much as 4 dB over a 10 to 60 degrees C operating range.

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Temperature Compensation Circuit for Edge Emitting LEDs

       Edge-emitting LEDs (ELEDs) offer better coupling of light
into fiber than surface-emitting LEDs (SLEDs).  However, the average
optical power of the ELED exhibits a much stronger dependence on
temperature and may vary by as much as 4 dB over a 10 to 60
degrees C operating range.

      The circuitry shown in the figure maintains the ELED's light
intensity by controlling the ELED drive current as a function of
temperature.  It boosts the drive current by typically 60 percent as
the temperature rises from 10 to 60 degrees C.  The output of the
compensation circuit drives a current mirror, which sinks current
from a current switch that drives the ELED.  As the temperature
increases, the compensation output increases in voltage, supplying
more current to the ELED driver.  The ELED's optical output remains
nearly constant because more current is driven through the diode as
its efficiency falls off with increasing temperature.

      The temperature compensation circuit is composed of two
sub-circuits, a temperature sensor and a current differencing
amplifier.  The temperature sensor provides an output voltage that
varies as a function of the chip junction temperature.  The current
differencing amplifier follows the voltage output of the temperature
sensor and creates an output capable of sourcing up to 16 mA.