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 The
figure to the right shows another ESD protection means commonly employed to protect laser
diodes. In this scheme, a Schottky diode is connected anti-parallel with
the laser diode. However, there are several problems with this technique.
First of all, most Schottky diodes were not designed
to handle nanosecond pulses of up to 50 amps. Within our testing using the
human body model, many Schottky diodes were themselves destroyed by an ESD
event of as little as 800 volts. Therefore, if the device that is put in
place as the ESD protection means is
destroyed by the ESD event, this is deemed to be an ineffective ESD
protection means.
Second, and more important, such a configuration
would only protect the laser diode from negative-ESD events (i.e., those
events that would tend to reverse-bias the laser diode). Positive-ESD
events are allowed to pass through to the laser diode without being
attenuated by a Schottky diode. Thus, at best, a Schottky diode is an
incomplete ESD protection means.
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ESD polarity terminology used on this
web site
The term “positive-ESD” is used to
mean electrostatic discharge (ESD) whose voltage polarity would tend
to forward-bias a laser diode. “Negative-ESD,” means ESD whose
voltage polarity would tend to reverse-bias a laser diode. |
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