differential line

    A kind of electrical connection using two wires,
   one of which carries the normal signal (V) and the other
   carries an inverted version the signal (-V).  A differential
   amplifier at the receiver subtracts the inverted signal from
   the normal signal to yield a signal proportional to V.  This
   subtraction is intended to cancel out any noise induced in the
   wires, on the assmption that the same level of noise will have
   been induced in both wires.  Twisted pair wiring is often
   used to try to ensure that this is the case.

   The two wires might be connected at the receiver to separate
   analogue to digital converters and the subtraction performed
   digitally.

   The RS-422 serial line standard specifies differential
   drivers and receivers, whereas the earlier RS-232 standard
   does not.

   Opposite: single ended.

   (1995-03-08)