CONTROL CIRCUIT OF AVALANCHE PHOTODIODE

摘要

PROBLEM TO BE SOLVED: To prevent a damage of an avalanche photodiode caused by an overcurrent generated at a rapid change of an optical input to the avalanche photodiode.

SOLUTION: The current flowing in the avalanche photodiode is forcibly shut off for a given length of time by a shuttoff circuit 4 when the current flowing in the avalanache photodiode is detected by a current detecting circuit 2 and the current determined by a determining circuit 3 exceeds the predetermined theshold. For instance, the shuttoff circuit 4 is composed of a one shot multivibrator circuit 5 which operates with an output of the determining circuit 3 as a trigger pulse. The one shot multivibrator circuit 5 outputs a pulse having a constant width regardless of the width of a trigger pulse input and shuts off the current by a current bypassing circuit 6 only for the period when the pulse is output.

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