Inverted phototransistor as a switched modulator
K. Beck · 1959
AN ALLOYED-JUNCTION PHOTOTRANSISTOR may be employed in the circuit illustrated, with the result that good thermal stability is obtained without requiring a modulated light source or thermally-sensitive compensating devices. In this circuit the phototransistor is operated in the inverted connection and has its light sensitivity gated electrically by a simple switching circuit. The leakage current is very nearly independent of the switching operation. The output is in the form of square wave pulses at the switching or carrier frequency and of amplitude determined by the light intensity.