PNP

from The Free On-line Dictionary of Computing (8 July 2008)
PNP

   1. <electronics> A type of {bipolar transistor} consisting of
   a layer of N-doped {semiconductor} (the "base") between two
   P-doped layers (the "collector" and "emitter").  PNP
   transistors are commonly operated with the emitter at {ground}
   and the collector at a negative {voltage}.

   In the 1960s, the germanium PNP transistor was the cheapest
   and best for use at ordinary temperatures.  The {leakage
   current} from collector to base in this type of device is
   larger than for the silicon transistor, and also varies more
   with temperature.  The effect of these deficiencies can be
   lessened by proper biasing and feedback, which can make the
   circuit both serviceable and reliable.  Neither germanium nor
   PNP transistors are as common today.

   The voltages used on a PNP transistor are inverted when
   compared with {vacuum tubes}.  Further, the behaviour of
   vacuum tubes is usually described in terms of {voltages}
   whereas transistors are better described in terms of
   {current}.

   2. <architecture> {plug and play}.

   (1997-05-05)