PHOTODIODE_LOG_CONVERTER_TRA_NSMITTER

Published:2009/6/22 23:00:00 Author:Jessie | From:SeekIC

A logarithmic conversion is made on the output current of a photodiode to compress a fourdecade, light-intensity variation into a standard transmission range. The circuit is balanced at midrange, where R3 should be chosen so that the current through it equals the photodiode current. The log-conversion slope is temperature compensated with R6. Setting the reference output to 1.22 V gives a current through R2 that is proportional to absolute temperature because of D1 so that this level-shift voltage matches the temperature coefficient of R6. C1 has been added so that large-area photodiodes with high capacitance do not cause frequency instabilities.



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