TWO-TERMINAL PHOTODETECTORS WITH INHERENT AC AMPLIFICATION PROPERTIES

摘要

A two-terminal photodetector comprising a photodiode and a plurality of active and passive components connected so that when connected to a source of current the voltage across the terminals is proportional to the illumination and is proportional by an amplification factor to rapidly changing illumination levels. In one embodiment the photodetector includes a first transistor having the photodiode connected in the emitter base circuit and a feedback resistor connected in the base collector circuit. This transistor is biased such that it is nearly saturated. Illumination on the photodiode causes the collector voltage to rise correspondingly. An output transistor is connected with its base joined to the emitter of the first transistor and a voltage divider connected between its emitter and collector. The output transistor has only a unity gain for low frequency signals but the gain is considerably increased for high frequency signals corresponding to rapidly changing illumination.