CHARACTERISTICS OF A CLASS OF NEW OPTO-COUPLER AMPLIFIERS WITH POSITIVE FEEDBACK

This paper discusses a new method of optoelectronic amplification that utilizes an array of one or more series connected light emitters (LED 's or laser diodes) from which the light is collected by closely coupl ed PIN diode detectors with high quantum efficiency, Positive current feedback is applied to the opto-coupler in order to increase the curre nt gain of the system, It is shown that the gain-bandwidth product of the system is proportional to the number of light emitters used, Curre nt, voltage, and power gains of the opto-amplifier are derived and typ ical results shown. The system noise becomes very small if devices of high current transfer efficiency are used, Further, the noise figure i s found to be independent of the positive feedback applied. For a give n system, there is a minimum noise figure, and it is independent of th e number of light emitters used in the array, With a transfer efficien cy of 0.95, a single light emitter opto-amplifier can provide a curren t gain of 14.7 dB with a noise figure of about 1.5 dB.