AVALANCHE PHOTODIODE QUENCHING CIRCUIT

摘要

An avalanche photodiode quenching circuit comprises a low value photodiode series resistor and a comparator amplifier. The comparator compares the photodiode potential with a reference voltage and changes state rapidly after initiation of a photodiode avalanche. The photodiode is actively quenched by taking its potential below breakdown. This is achieved by a fast-switching transistor activated by avalanche detection at the comparator. A further fast-switching transistor is arranged to reset the comparator input after a preset delay following avalanche detection. The photodiode recharges passively through the series resistor at a rapid rate since this resistor has a low value. The quench and reset transistors are deactivated by comparator reset, the latter after the preset delay once more, and are isolated from the photodiode 12 during recharge by diodes 16 and 18. The invention avoids the use of active photodiode reset pulses, and has constant output pulse width and well defined dead-time.