18WuD2x

188 diffused transistor • digital comparator
diffused transistor A transistor in which one or
both electrodes are created by diffusion. See DIF-
FUSED JUNCTION.
diffused-junction transistor See DIFFUSED-
BASE TRANSISTOR, DIFFUSED-MESA TRAN-
SISTOR, and DIFFUSED TRANSISTOR.
diffusion 1. In the fabrication of semiconductor
devices, the slow, controlled introduction of a material
into the semiconductor, for example, the
high-temperature diffusion of a n-type impurity
(from a gas containing it) into a p-type wafer to
form a diode. 2. The random velocity and movement
of current carriers in a semiconductor, resulting
from a high-density gradient. 3. The
characteristic spreading of light reflected from a
rough surface or transmitted through a translucent
material. 4. The spreading-out of sound
waves, for example when reflected from acoustic
baffles. 5. The migration of atoms from one substance
to another, as in the spreading of one gas
throughout another.
Incident
rays
Translucent
material
diffusion, 3
Transmitted
rays
diffusion bonding A method of joining different
substances by diffusing atoms of one into the
other. This technique is employed in the manufacture
of certain semiconductor diodes, transistors,
and other devices.
diffusion capacitance The current-dependent capacitance
of a forward-biased semiconductor
junction.
diffusion current Current resulting from the diffusion
of carriers within a substance (see DIFFU-
SION, 2).
diffusion length In a semiconductor junction, the
distance a current carrier travels to the junction
during carrier life.
diffusion process 1. The technique of processing
semiconductor devices by diffusion (see DIFFU-
SION, 1). 2. Producing a high vacuum by means
of diffusion (see DIFFUSION PUMP).
diffusion pump A pump for fast, efficient creation
of a high vacuum in electron tubes and similar
devices. In one form, the pump, in conjunction
with a force pump, uses mercury vapor as the
pumped medium. Gas molecules evacuated from
the device diffuse into a chamber, where condensing
mercury vapor traps and carries them
off.
diffusion theory The notion that, in a homogeneous
medium, current density is directly
proportional to the gradient of particle flux
density.
diffusion transistor A transistor whose operation
is based principally on the diffusion of current
carriers (see DIFFUSION, 2).
diffusor In acoustics, a device or structure deliberately
installed to spread sound waves throughout
a region.
dig-in angle A stylus angle of 90 degrees, relative
to the surface of a phonograph disc. Compare
DRAG ANGLE.
DIGIRALT Acronym for digital radar altimetry. A
system that utilizes digital techniques to enhance
the accuracy of an altimeter using radar.
digit A single symbol in a numbering system (e.g.,
0 through 9 in the decimal system, or 0 or 1 in
the binary system), whose value depends on its
position in a group and on the radix of the particular
system used.
digital 1. Pertaining to components, circuits, or
systems that use signals having an integral number
of discrete levels or values, rather than signals,
whose levels or values vary over a
continuous range. 2. Pertaining to a numeric
readout or display. 3. See BINARY, 1.
digital annunciator An annunciator that gives an
alphanumeric digital display of information, as
well as sounding an alarm.
digital audio tape Abbreviation, DAT. A magnetic
tape intended for recording digitally encoded audio
data. Used in some high-fidelity applications,
and also for computer data storage.
digital barometer An electronic barometer providing
a digital readout.
digital capacitance meter Abbreviation DCM. A
meter with a digital readout for measuring capacitance
values.
digital cellular See PERSONAL COMMUNICA-
TIONS SERVICE.
digital circuit A circuit affording a dual-state
switching operation (i.e., on or off, high or low,
etc.). Also called binary circuit.
digital communications Radio or wire communications
using a dual-state mechanism (on/off,
positive/negative, or modulated/unmodulated)
to represent information.
digital comparator A comparator that presents
two digital values, one for each of the quantities
being compared.