Techniques
Electronic Military & Defense Annual Resource, 6th Edition
17
a multiplexer that is fast might not mean much if it cannot
handle single-event effects (SEE) or total ionizing dose (TID).
TID results in threshold shifts for CMOS devices, while SEE
becomes more of an issue as the feature size decreases with
low-voltage devices. Sometimes, a multiplexer malfunction
can be a minor glitch, but other times the result can be
catastrophic.
If the analog multiplexer cannot withstand single-event
transients (SET), its output could momentarily transition
to another channel without the knowledge of the
microprocessor, and the microprocessor could subsequently
read the data as a malfunction. After the output recovers,
the system reads normal again. An error like this is a minor
annoyance and can be programmed out just by making
sure the signal persists longer than a predefined time before
reading it as valid data — this increases reaction time by
adding propagation delay.
If an analog multiplexer has ways to handle SEE, the
need for a programmed delay is all but eliminated, and the
microprocessor can treat all incoming data as valid. Single-
event burnout (SEB) and single-event latch-up (SEL) can
interrupt the normal function of an analog multiplexer. SEB
results in a non-functioning multiplexer, where SEL may be
reversed with a power cycle but can lead to immediate or
latent damage. TID's threshold-shifting nature also could
cause a multiplexer to stop working altogether. Thankfully,
lower-voltage devices are less prone to threshold movement,
due to their thinner gate oxides.
There are many more single-event effects, but, from an
application standpoint, the phenomena described here
are the primary concerns for analog multiplexers. Figure 2
depicts an ISL71830SEH 16-channel multiplexer test plot of
an SET for linear energy transfer (LET).
Figure 2: Composite plot of SET for LET = 43MeV•cm2/mg in test with
+5.5V supplies
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