18WuD2x

decommutator • definite-purpose component 173
decommutator A circuit or device for performing
decommutation, including demodulators, demultiplexers,
and signal separators.
decoupler A device that isolates two circuits so
that a minimal amount of coupling exists between
them.
decoupling The elimination or effective minimization
of coupling effects, as in decoupling amplifier
stages to prevent interaction through a common
power-supply lead.
decoupling capacitor 1. A capacitor that provides
a low-impedance path to ground to prevent
undesired stray coupling among the circuits in a
system. 2. The capacitive member of a resistancecapacitance
(RC) decoupling filter.
decoupling filter A resistance-capacitance (RC) filter,
usually inserted into a common dc line in a
multistage amplifier to prevent interstage feedback
coupling through the common impedance of
the line.
decoupling network One or more decoupling filters.
decoupling resistor The resistive member of a resistance-capacitance
(RC) decoupling filter.
decoy In radar, an object that provides misleading
reflections. Also see CHAFF.
decreasing function A function whose curve has a
negative slope at all points in the domain.
decrement 1. Also called logarithmic decrement.
The rate at which a damped wave dies down. The
decrement value is the natural (base-e) logarithm
of the ratio of two successive peaks of the same
polarity. 2. A quantity used to lessen the value of
a variable. 3. To lower the value (of a register, for
example) by a single increment.
decremeter An instrument for measuring the decrement
of a radio wave.
decremeter capacitor A variable capacitor for use
in a decremeter. The rotor plates are shaped so
that equal angular rotations correspond to the
same decrement at all settings. Thus, the percentage
of capacitance change for a given angle of rotation
is constant throughout the capacitance range.
decryption The conversion of an encrypted signal
from a cipher into plain text, graphics, or other
commonly recognizable form. Also see CIPHER.
Compare ENCRYPTION.
decryption key An algorithm, or a set of algorithms,
that converts an encrypted signal from a cipher
into plain text, graphics, or other commonly recognizable
form. Each cipher has its own unique
algorithm or set of algorithms for this purpose.
The signal cannot be decrypted unless all the
components of the key are present.
dedicated Assigned exclusively to a certain purpose
[e.g., a dedicated facsimile (fax) line].
deductive logic A form of symbolic logic used to
demonstrate that a certain conclusion will always
follow, given a certain set of circumstances. The
logic of digital circuits is deductive. Compare IN-
DUCTIVE LOGIC.
dee In a cyclotron, one of the D-shaped chambers
in and between which particles accelerate in a
spiral path to high velocity.
dee line In a cyclotron, a support for the dee, with
which it forms a resonant circuit.
deemphasis In frequency modulation, the introduction
of a low-pass characteristic (response
falls as modulating frequency increases) to complement
the rising response of preemphasis. Also
called postemphasis or postequalization. Compare
PREEMPHASIS.
deemphasis amplifier An amplifier used to remove
the high-frequency preemphasis applied to
signals prior to broadcasting, multiplexing, tape
recording, or telemetering. Also see DEEMPHA-
SIS and PREEMPHASIS.
deemphasis circuit A low-pass filter that provides
deemphasis in an FM receiver.
deemphasis network See DEEMPHASIS CIRCUIT.
deenergize To take a circuit or device out of operation
(i.e., to remove its power or signal excitation).
deep cycle Pertaining to a rechargeable cell or battery
that can operate until it is almost completely
discharged. It generally has a high ampere-hour
capacity.
deep-diffused junction A pn junction made by diffusing
the impurity material deep in the semiconductor
wafer. Compare SHALLOW-DIFFUSED
JUNCTION.
deep discharge The nearly complete discharge of a
cell or battery; usually done prior to recharging.
deep-space net A radar system intended for constant
monitoring of spacecraft.
defeating 1. The disabling or circumvention of an
alarm or security system, leaving the protected
property vulnerable to intrusion. 2. The dangerous,
and potentially lethal, disabling of a safety
device in an electrical or electronic system.
defect 1. Absence of an electron (hence, presence
of a hole) in the lattice of a semiconductor crystal.
2. An abnormality of design, construction, or performance
of an electronic circuit or device. 3. In a
computer system, a hardware or software fault
that could be the eventual cause of a failure. 4. A
flaw in a crystalline substance.
defect conduction In a semiconductor material,
conduction via holes.
deferred addressing Indirect addressing in which
a preset counter makes several references to find
a desired address.
deferred entry An entry into a computer subroutine,
delayed because of a delay in the exit from a
control program.
deferred exit An exit from a computer subroutine,
delayed because of a particular command.
defibrillation Use of a CARDIAC STIMULATOR to
halt fibrillation of the heart, as caused by electric
shock.
defibrillator See CARDIAC STIMULATOR.
definite-purpose component A component designed
for a specific use, rather than for a wide