ThingMagic Micro Hardware - Manual (Page 101)

ElectroStatic Discharge (ESD) Considerations
A D I V I S I O N O F T R I M B L E
96 Appendix C: Environmental Considerations
has returned to the bootloader to prevent any further damage. This jump to boot
loader caused by power amp damage occurs at the start of any read tag commands.
Ultimately determining that ESD is the root cause of failures is difficult because it relies on
negative result experiments, i.e. it is the lack of failure after a configuration change, rather
than a positive flag wave that says “I’m ESD”. Such flag waves are sometimes, but only
sometimes, available at the unpackaged transistor level under high power microscopy.
The remoteness of microscopic examination from the installed field failures is indicative of
the high cost of using such analysis methods for chasing down ESD issues. Therefore
most ESD issue resolutions will be using the negative result experiments to determine
success.
ESD discharges come with a range of values, and like many things in life there is the
“matter of degree”. For many installations, the Micro has been successfully deployed and
operates happily. For these, there is no failure issue, ESD or otherwise. For a different
installation that with bare Micro, has a failure problem from ESD, there will be some
distribution of ESD intensities occurring. Without knowledge of a limit in the statistics of
those intensities, there may always be the bigger zap waiting in the wings. For the bare
Micro equipped with the mitigation methods described below, there will always be the
rouge ESD discharge that exceeds any given mitigation, and results in failure.
Fortunately, many installations will have some upper bound on the value of ESD events
given the geometry of that installation.
Several sequential steps are recommended for a) determining the ESD is the likely cause
of a given group of failures, and b) enhancing the Micro’s environment to eliminate ESD
failures. The steps vary depending on the required Micro output power in any given
application.
Identifying ESD as the Cause of Damaged Readers
The following are some suggested methods to determine if ESD is a cause of reader
failures, i.e. ESD diagnostics. Please remember- some of these suggestions have the
negative result experiment problem.
Return failed units for analysis. Analysis should be able to say if it is the power
amplifier that has in fact failed, but won’t be able to definitively identify that the cause
is ESD. However, ESD is one of the more common causes of PA failure.
Measure ambient static levels with static meter. AlphaLabs SVM2 is such a meter, but
there are others. You may be surprised at the static potentials floating detected.
However, high static doesn’t necessarily mean discharges, but should be considered
cause for further investigation. High levels that keep changing are highly indicative of
discharges.
Touch some things around the antenna, and operating area. If you feel static
discharges, that qualitatively says quite a bit about what is in front of the antenna.