Low frequency noise as a tool to study optocouplers with phototransistors

摘要

An approach to analyze the optocouplers with phototransistors by low frequency noise measurements is presented in this paper. The analysis is based on the measurements of LED and output noises of optocouplers. We have shown that the corner frequency in output noise can be caused by frequency dependence of dynamic current gain of phototransistor under conditions of open base circuit. A noise parameter as an indicator of optocoupler's phototransistor current gain degradation is proposed. The contributions of noise sources of LED and phototransistor to the frequency dependence of the output noise spectrum are also considered.