Trends in optocoupler radiation degradation

Proton-radiation test results for new optocoupler technologies are compared with those of older optocouplers. The new devices are far more resistant to displacement damage effects and have a much higher current-transfer ratio (CTR). The improvements are due to improved optical-coupling efficiency in combination with light-emitting diode (LED) technologies that are inherently more resistant to lifetime degradation. Because of these changes, CTR degradation is no longer dominated by LED damage. LED degradation, gain degradation, and photoresponse degradation all contribute to the overall changes in CTR after irradiation in the newer device types.

I. Introduction

Optocouplers are simple devices compared to conventional integrated circuits, but they have proven to be somewhat difficult to use in space because they require high internal gain to amplify photocurrent produced by internal light-emitting diodes (LEDs) (net power transfer from the LED to the photodetector is on the order of 0.1%). Space failures have occurred from two different mechanisms: displacement damage from high-energy protons, which produces TABLE I Properties of the Optocouplers Used in the Study

Device	Manu- facturer	Input Current (mA)	Current Transfer Ratio	LED Technology
6N139	Agilent	0.5	20	Double-Het
HCPL4701	Agilent	0.04	35	Double-Het
HCNR200	Agilent	0.1–10	0.005*	Double-Het.
4N49	Micropac	1	2	Amphoteric
*The HCNR200 contains no active gain elements. The current transfer ratio is the ratio between current in either of the two photodiodes to the forward current of the LED.