Electrical Engineering Dictionary - part 8

Transformer with additive polarity.

of errors in the channel can be modeled as
the addition of random noise with a Gaus-
sian distribution and a constant (white) power
spectrum. See also

thermal noise

address

a unique identifier for the place

where information is stored (as opposed to
the contents actually stored there). Most stor-
age devices may be regarded by the user as a
linear array, such as bytes or words in RAM
or sectors on a disk. The address is then just
an ordinal number of the physical or logical
position. In some disks, the address may be
compound, consisting of the cylinder or track
and the sector within that cylinder.

In more complex systems, the address

may be a “name” that is more relevant to the
user but must be translated by the underlying
software or hardware.

address aliasing

See

cache aliasing

address bus

the set of wires or tracks

on a backplane, printed circuit board, or in-
tegrated circuit to carry binary address sig-
nals between different parts of a computer.
The number of bits of address bus (the width
of the bus) determines the maximum size of
memory that can be addressed. Modern mi-
crochips have 32 address lines, thus 4 giga-
bytes of main memory can be accessed.

address decoder

logic that decodes an

address.

1. A partial decoder responds to a small

range of addresses and is used when recog-
nizing particular device addresses on an I/O
address bus, or when recognizing that ad-
dresses belong to a particular memory mod-
ule.

2. A full decoder takes

N bits and asserts

one of 2

outputs, and is used within mem-

ories (often within RAM chips themselves).

address error

an exception (error inter-

rupt) caused by a program’s attempt to access
unaligned words or long words on a proces-
sor that does not accommodate such requests.
The address error is detected within the CPU.
This contrasts with problems that arise in ac-
cessing the memory itself, where a logic cir-
cuit external to the CPU itself must detect and
signal the error to cause the CPU to process
the exception. Such external problems are
called bus errors.

address field

the portion of a program

instruction word that holds an address.

address generation interlock (AGI)

mechanism to stall the pipeline for one cycle
when an address used in one machine cycle
is being calculated or loaded in the previous
cycle. Address generation interlocks cause
the CPU to be delayed for a cycle. (AGIs
on the Pentium are even more important to
remove, since two execution time slots are
lost).

address locking

a mechanism to protect

a specific memory address so that it can be
accessed exclusively by a single processor.

address map

a table that associates a base

address in main memory with an object (or
page) number.

address mapping

the translation of vir-

tual address into real (i.e., physical) ad-
dresses for memory access. See also

virtual

memory

address register

a register used primarily

to hold the address of a location in memory.
The location can contain an operand or an
executable instruction.

address size prefix

a part of a machine

instruction that provides information as to the

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length or size of the address fields in the in-
struction.

address space

an area of memory seen or

used by a program and generally managed as
a continuous range of addresses. Many com-
puters use separate address spaces for code
and data; some have other address spaces
for system. An address space is usually sub-
ject to protection, with references to a space
checked for valid addresses and access (such
as read only).

The physical address space of a computer

bytes, and up to 2

bytes) is often larger

than the installed memory. Some parts of the
address range (often at extreme addresses)
may be reserved for input–output device ad-
dresses. See also

byte

memory

mapped I/O

address translation

See

address mapping

addressing

(1) in processors: a mecha-

nism to refer to a device or storage location by
an identifying number, character, or group of
characters. That may contain a piece of data
or a program step.

(2) in networks, the process of identify-

ing a network component, for instance, the
unique address of a node on a local area net-
work.

addressing fault

an error that halts the

mapper when it cannot locate a referenced
object in main memory.

addressing mode

a form of specifying

the address (location) of an operand in an
instruction. Some of the addressing modes
found in most processors are direct or register
direct, where the operand is in a CPU register;
register indirect (or simply indirect), where
a CPU register contains the address of the
operand in memory; immediate, where the
operand is a part of the instruction. See also

central processing unit

addressing range

numbers that define

the number of memory locations addressable
by the CPU. For a processor with one address
space, the range is determined by the number
of signal lines on the address bus of the CPU.

adequate service

in terms of the block-

ing probability, term associated with a fixed
blocking. A typically quoted value may be
2. See also

blocking

adiabatic

a system that has no heat trans-

fer with the environment.

adiabatic cooling

a process where the

temperature of a system is reduced without
any heat being exchanged between the sys-
tem and its surroundings. In particle beam
acceleration this term is used to describe the
process in the particle source storage ring
where beam emittances are reduced without
affecting beam energy.

adiabatic following

an approximation

made when some states in a quantum me-
chanical system respond to perturbations
more quickly than the other states. In this
approximation the rapidly responding states
are assumed to depend only on the instanta-
neous values of the other states and are said
to “follow” those states.

adiabatic passage

a technique for the cre-

ation of a long-lived coherence in a quantum
mechanical system by manipulating electro-
magnetic field intensities so that the system
always remains in an eigenstate. In practice,
this involves changing field strengths on a
time scale slower than the inverse of the en-
ergy spacing between relevant eigenstates of
the system. For example, consider a lambda
system in which only one field is present ini-
tially and all population starts out in the un-
coupled ground state. If a field is gradually
turned on to couple this initial state to the ex-
cited state, the system can remain transparent
by evolving in such a way that it is always
mathematically equivalent to the dark state
that would be produced by coherent popu-

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lation trapping. Adiabatic passage is often
used for selective transfer of population be-
tween two long-lived states of a multistate
system, especially in cases where the two-
step process of absorption followed by spon-
taneous decay (optical pumping) would tend
to populate many other states.

adjacency graph

a graph in which each

node represents an object, component, or fea-
ture in an image. An edge between two nodes
indicates two components that are touching
or connected in the image.

adjacent channel interference (ACI)

the

interference caused by an adjacent frequency
band, e.g., in a system with frequency divi-
sion duplex (FDD). Classified as either in-
band or out-of-band adjacent channel inter-
ference (ACI). The in-band ACI occurs when
the center frequency of interfering signal falls
within the band of the desired signal. The
out-of-band ACI occurs when the center fre-
quency of interfering signal falls outside the
bandwidth of the desired signal.

adjacent channel leakage power

See

adjacent channel power

adjacent channel power (ACP)

a power

of distortion components generated in adja-
cent channel, which is caused by a nonlinear-
ity of high-power amplifier amplifying a dig-
itally modulated signal such as QPSK, QAM,
etc. Adjacent channel power is defined as a
ratio of signal power in channel and leakage
power in adjacent channel.

adjacent channel reuse ratio (ACRR)
the reuse ratio between radio communication
cells using adjacent radio channels. See also

reuse ratio

adjacent channels

radio channels occu-

pying radio frequency allocations

n and n±1.

adjoint network

a network with an iden-

tical structure to the original one, but with
possibly different elements. As an exam-

ple, for a network described by the nodal ad-
mittance matrix, its adjoint network is repre-
sented by the transposed admittance matrix
of the original network. The adjoint network
is a basic tool in the computer-aided sensi-
tivity analysis of electronic and microwave
circuits.

adjustable-speed drive

See

variable

speed DC drive

variable speed AC drive

admissible matrix

a matrix

−

that can

be obtained by fixing the free parameters of
the matrix

M at some particular values. M

−

is said to be admissible with respect to

admittance

the reciprocal of the

impedance of an electric circuit.

admittance inverter

an idealized de-

vice or set of matrix parameters that func-
tions electrically like a quarter-wave lossless
transmission line of characteristic impedance
J at each frequency, thus transforming the
load admittance (

LOAD

) by

+90 degrees and

modifying the magnitude, resulting in an in-
put admittance (

load

admittance matrix

the inverse of the

impedance matrix in the method of moments.

ADP

See

ammonium dihydrogen phosphate

ADPCM

See

adaptive differential pulse

code modulation

ADSL

See asymmetric digital subscriber

line.

adsorbent

the material of an adsorber,

for example, silica gel, alumina, and char-
coal. Adsorbent materials are characterized
by high surface to volume ratio.

adsorber

(1) condensation of a gas on the

solid material.

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(2) material that attracts and holds (by Van

der Waal forces) molecular layers of dense
gases (i.e., very near condensation temper-
atures) on porous high surface/volume ratio
materials.

ADTV

See

advanced digital television

advanced compatible television (ACTV)

an extended definition television system that

can operate with existing bandwidths on ex-
isting receivers and is compatible with the
NTSC broadcasting system. The ACTV sys-
tem was proposed by the Advanced Televi-
sion Research Consortium and was the first
high definition television (HDTV) system.
HDTV system was tested by the FCC July
17, 1992. The additional picture information
needed to increase the picture width and to
increase the resolution to the HDTV format
is transmitted in an augmented channel as
an alternative to simulcast transmission. See

Advanced Television Research Consortium

advanced digital television (ADTV)
a high definition television (HDTV) digital
transmission television system was proposed
to the Federal Communications Commission
by the Advanced Television Research Con-
sortium. The ADTV system introduced a
layered system to separately describe the dig-
ital transmission system, the video compres-
sion system, and the data packet transport
system. The video compression method uses
a MPEG

++ standard that provides for com-

patibility with multimedia computing. See

Advanced Television Research Consortium

advanced mobile phone system (AMPS)

a standard for a cellular radio communi-

cations network originally developed in the
1970s by AT&T and later adopted as an in-
dustry standard by the U.S.-based Telecom-
munications Industries Association (TIA). It
is the first cellular standard widely deployed
in North America. It is also referred to as the
analog cellular system. Frequency modula-
tion with 30 kHz channels is used.

Advanced Television Research Consor-
tium

an organization consisting of David

Sarnoff Research Center, Thompson Con-
sumer Electronics, North American Philips
Corporation, NBC, and Compression Labo-
ratories.

aeolian vibration

a high-frequency me-

chanical vibration of electric power lines
caused by wind.

aerial cable

any fully-insulated electric

power cable which is carried overhead upon
poles, as opposed to the use of the more usual
overhead bare conductors.

aerodynamic head

See

disk head

AFC

See

automatic frequency control

affine transform

a geometric image

transformation including one or more transla-
tions, rotations, scales, and shears that is rep-
resented by a 4

× 4 matrix allowing multiple

geometric transformations in one transform
step. Affine transformations are purely lin-
ear and do not include perspective or warping
transformations.

AFM

See

atomic force microscope

AFT

See

automatic fine tuning

AFV

See

audio follow-video switcher

AGC

See

automatic gain control