Study of Amplification in Optocoupler-Equivalent Circuits

A report presents a theoretical and experimental study of amplification in electronic circuits that include combinations of discrete light sources (e.g., lightemitting diodes) and photodetectors (e.g., reverse-biased photodiodes), which combinations perform essentially the same functions as do the commercially available, packaged lightsource/ photodetector combinations denoted, variously, as optocouplers, optoisolators, and the like. The report calls these circuits photo-electric amplifiers (which should not be confused with photoelectric amplifiers). The report discusses the basic considerations of current, voltage, impedance, transformer coupling, source/detector optical coupling, bias and load resistances, and other phenomena that affect current, voltage, and power gains. Limitations and design concerns for making photoelectric amplifiers function as linear amplifiers are also discussed. Tests of amplifiers and oscillators based on photo-electric amplifiers are described. An addendum to the report discusses the use of photo-electric amplifiers to make digital-logic elements for data-processing circuits ranging from process controllers to computers. Finally, it is reported that experimental AND, OR, and NOT gates were constructed and tested to demonstrate this concept and were found to function as predicted.