An inverter is an
electronic component used in
digital systems that takes the
logical value of its
input and
complements it. So, if the
input voltage is logically
low, a
high voltage appears on the
output, and
vice versa. The exact values of the
high and
low voltages depend on the
semiconductor family. See
CMOS,
TTL.
Here are a few symbols for the same piece of hardware, depending upon the desired use. Also, a polarity indicator (wedge) might replace the bubble.
Hi -> Lo Lo -> Hi In | Out
----+----
|\ |\ H | L
-| \o- -o| \-- L | H
| / | /
|/ |/