GREENSBORO, N.C., 16 July 2009. Suppliers of radiation hardened analog to digital converters and digital to analog converters for space electronics applications face a more difficult set of design challenges than do suppliers of A/D and D/A converters for commercial applications.
"We have constraints such as traceability, radiation performance, and a long list of items," says Bob Barfield, business development manager for the Analog Devices Inc. space products segment in Greensboro N.C.
Barfield says he is seeing an increase in mil spec kinds of requirements for rad hard electronic components intended for space avionics -- particularly A/D and D/A converters. "From a U.S. defense space market perspective, we are seeing more and more contract flow-down requirements requiring QML V or QML R space parts," he says. The space market requires traceability and process control.
A/D and D/A converter providers (see related story Military A/D and D/A converters come to grips with a complex, network centric world) for space applications are particularly concerned with what they call low radiation dose performance -- or the amount of space radiation that their components must endure over time.
"Right now we are looking at 10 millirads per second," Barfield says. "Over time there are a lot of industry experts who determine that at lower dose rates we can see performance degradations not observable at higher dose rates."
One of the problems of designing electronic components for space applications is the physical changes these components undergo over time while operating in space. "It's sometimes not enough to characterize a certain wafer lot, and five years down the road to expect they are still at the same performance level," Barfield says.
"It is really, really process-dependent how vulnerable the ADCs are to radiation," Barfield continues." SOI [silicon-on-insulator technology] is tolerant of SEU [radiation-induced single-event upsets] and ionizing dose. If we move to more digital-type processes like CMOS, there is increased susceptibility to single-event effects. We need to be relatively careful in our characterization of parts."