18WuD2x

negative resistance • nemo 471
voltage across it increases, and an increase in
current as the voltage decreases. This is opposite to
the behavior of an ohmic (positive) resistance. Also
see N-CURVE, NEGATIVE-RESISTANCE REGION,
NEGATIVE RESISTOR, and S CURVE.
+
Current
Negative
resistance
region
negative resistance
+
Voltage
negative-resistance amplifier A simple circuit in
which a negative-resistance device, such as a
TUNNEL DIODE, cancels the positive resistance
of the circuit, causing amplification or oscillation.
negative-resistance device See NEGATIVE RE-
SISTOR.
negative-resistance diode 1. See TUNNEL DIODE.
2. A reverse-biased germanium diode (and occasionally
a silicon diode) that exhibits NEGATIVE
RESISTANCE. 3. A special diode tube that, when
operated at ultrahigh frequencies, exhibits negative
resistance because of transit-time effects.
negative-resistance magnetron A split-anode
magnetron operated at a combination of anode
voltage and magnetic field strength corresponding
to cutoff; it exhibits negative resistance to
voltage applied symmetrically between the anode
halves. The frequency of oscillation is determined
by an external tank circuit.
negative-resistance oscillator An oscillator that
consists of a negative-resistance device connected
across a tuned circuit. The arrangement
oscillates because the negative resistance cancels
the positive resistance (losses) of the tuned circuit.
See, for example, NEGATIVE-RESISTANCE
MAGNETRON and TUNNEL-DIODE OSCILLA-
TOR.
negative-resistance region In certain devices, a
portion of the voltage-versus-current curve having
negative slope (i.e., the current decreases as
the voltage increases, or vice versa). Also see N
CURVE, NEGATIVE RESISTANCE, and S CURVE.
negative-resistance repeater A repeater that produces
gain by means of NEGATIVE RESISTANCE
effects.
negative resistor Any device exhibiting NEGATIVE
RESISTANCE.
negative space charge The cloud of electrons
(negative particles) in the region surrounding an
emitter, such as the hot cathode of a vacuum
tube.
negative temperature coefficient Abbreviation,
NTC. A number expressing the amount by which
a quantity (such as the rating of a component) decreases
when the temperature is raised. The coefficient
is stated as a percentage, or as a certain
number of parts per million (ppm) per degree
temperature rise. Compare POSITIVE TEMPERA-
TURE COEFFICIENT and ZERO TEMPERATURE
COEFFICIENT.
negative terminal See NEGATIVE ELECTRODE,
2.
negative torque In an electric motor, a torque that
acts against the operating torque.
negative transmission In a television or facsimile
system, the condition in which brighter light corresponds
to lower transmitted power, and dimmer
light corresponds to higher transmitted power.
negative valence The valence of a negative ion.
Also see VALENCE.
negator A logical NOT element [i.e., one that outputs
the complement of an input bit (1 for 0 and
vice-versa)].
negatron The term that specifically differentiates
the familiar ELECTRON from a POSITRON (positive
electron).
NEI Abbreviation of noise equivalent input.
neighborhood node A local site at which a fiberoptic
television (video) signal is converted to a cable
signal.
NEL Abbreviation of National Electronics Laboratory.
NELA Abbreviation of National Electric Light Association.
N electron In certain atoms, an electron whose orbit
is outside of, and nearest to, those of the M
electrons.
NEMA Abbreviation of National Electrical Manufacturers’
Association.
nematic crystal A normally transparent liquid
crystal that becomes opaque when an electric
field is applied to it, and becomes transparent
again when the field is removed. The crystal material
is cut in the form of a letter or numeral and
provided with a reflecting backplate for display
readouts in calculators, watches, and various
electronic devices.
nematic-crystal display A device in which an electrically
controlled film of nematic-crystal material
is used to transmit and interrupt light from a
lamp or from a reflecting mirror, in this way displaying
characters in whose shape the film has
been formed.
nematic liquid In a liquid-crystal display (LCD), a
normally clear liquid that becomes opaque in the
presence of an electric field.
nemo A radio or television program that is picked
up from a location outside the studio. Also called
field pickup or remote.