Electrical Engineering Dictionary - part 163

some type of diversity combining. See also

soft iron

a term used to describe iron that

has a low coercivity. Note that soft refers to
the magnetic properties of the material, not
necessarily the physical properties.

soft magnetic material

a magnetic ma-

terial that does not retain its magnetization
when the magnetizing field is removed; a ma-
terial with low coercivity and high permeabil-
ity.

soft real-time

See

soft real-time system

soft real-time system

a real-time system

in which failure to meet deadlines results in
performance degradation but not necessarily
failure. Compare with

firm real-time

hard

real-time

soft switching

the control of converter

switching in order to utilize device and com-
ponent parasitics and resonance conditions to
enable zero current switching (ZCS) or zero
voltage switching (ZVS), thereby reducing
switching losses, stress and EMI. Typically
this is performed with additional resonant
components and switches that are activated
only during the switching transients.

Soft switching also allows higher switch-

ing frequencies in order to reduce the con-
verter size and weight, thus increasing the
power density.

softbake

See

prebake

soft-decision decoding

decoding of en-

coded information given an unquantized (or
finely quantized) estimate of the individually
coded message symbols (for example, the
output directly from the channel). Compare
with

hard-decision decoding

soft-starter

a motor starter that provides

a ramp-up of voltage supplied to the motor
at starting with the objective of reducing the
starting current and torque.

soft X-ray lithography

See

EUV

lithography

softer hand-off

similar to the concept of

soft hand-off except that it involves transmis-
sion/reception through multiple antenna sec-
tors of the same cell as opposed to multiple
base stations. In contrast to soft hand-off,
softer hand-off need not involve the mobile
telephone system switch in the hand-off pro-
cess.

software design

a phase of software de-

velopment life cycle that maps what the sys-
tem is supposed to do into how the system
will do it in a particular hardware/software
configuration.

software development life cycle

a way to

divide the work that takes place in the devel-
opment of an application.

software engineering

systematic devel-

opment, operation, maintenance, and retire-
ment of software.

software evolution

the process that adapts

the software to changes in the environment
where it is used.

software interrupt

a machine instruction

that initiates an interrupt function. Software
interrupts are often used for system calls, be-
cause they can be executed from anywhere in
memory and the processor provides the nec-
essary return address handling. Also known
as a supervisor call instruction (SVC) (IBM
mainframes) or INT instruction (Intel X86).

software reengineering

the reverse anal-

ysis of an old application to conform to a new
methodology.

soil electrode

an electrical connection to

the soil, often in the form of a metal stake
driven into the earth.

solar–thermal–electric conversion

col-

lection of solar energy in thermal form using

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flat-plate or concentrating collectors and its
conversion to electrical form.

solder duration

See

solder profile

solder profile

the time versus temper-

ature profile required to properly solder a
connection without damaging the component
to either side of the connection, and with-
out leaving any defects in the solder joint.
The solder profile will include preheating,
ramp-up, time at solder reflow temperature,
ramp-down, and any relevant limits in time
and temperature. The profile will be specific
to a given system (components, materials,
plating, fluxes or gases, solder type, surface
preparation, etc.).

solder temperature

See

solder profile

sole

a nonemitting cathode.

solenoid

a wound cylindrical and mag-

netic material assembly used typically for
producing linear motions.

solid laser

laser in which the amplifying

medium is a solid.

solid state disk (SSD)

very large-

capacity, but slow, semiconductor memory
that may be used as a logical disk, extended
main memory, or as a logical cache be-
tween main memory and conventional disk.
SSD is typically constructed from DRAM
and equipped with a battery to make it non-
volatile. First used in IBM 3090 and Cray-
XMP computer systems.

solid state laser

laser in which the ampli-

fying medium is a solid, sometimes consid-
ered to exclude semiconductor lasers.

solid state power amplifier (SSPA)

high-power, multistage amplifier using semi-
conductor devices.

solid state relay

a protective relay that

employs analog electronics, logic electron-

ics, and magnetics to implement the operat-
ing logic.

solid state ultraviolet laser

an ultraviolet

laser made from a solid state or semiconduc-
tor material, e.g., Nd:LaF3, Ce:LaF.

solid state UV laser

See

solid state

ultraviolet laser

solidly grounded

an electrical distribu-

tion system in which one of the normal
current-carrying conductors, often the neu-
tral, is intentionally connected to ground with
no impedance other than that of the conduc-
tor comprising the connection.

solidly grounded system

a grounding

scheme in which the neutral wire of a power
system is connected to ground at frequent in-
tervals so as to minimize the impedance be-
tween neutral and ground.

soliton

an optical pulse that preserves its

shape while propagating by balancing fiber
dispersion and nonlinearity.

soliton transmission system

often termed

the fifth generation of fiber optic communi-
cation systems. See also

soliton

solution domain

electromagnetic fields

can be represented as a function of time, or
a time-domain description, or as a function
of frequency using a (usually) Fourier trans-
form, which produces a frequency-domain
description.

SOM

See

self organizing map

sonar

acronym for “sound navigation and

ranging” adopted in the 1940s, involves the
use of sound to explore the ocean and under-
water objects.

sonar equation

See

figure of merit

SONET

See

synchronous optical network

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sonorant

the class of phonemes with a

formant-like spectrum. For example, vowels
and nasals exhibit a spectrum that is based on
formants.

SONT

See

self-organizing neural tree

SOP

See

sum of products

sound carrier

in a TV signal, the FM

carrier that transmits the audio part of the
program.

sound velocity profile (SVP)

description

of the speed of sound in water as a function
of water depth.

source

(1) refers to the signal genera-

tor/device that generates the RF, microwave,
or micromilliwatt frequencies.

(2) the terminal of a FET from which elec-

trons flow (electrons in the FET channel flow
from the source, and current flow is always in
the negative direction of electron movement,
since electrons are negative). It is usually
considered to be the metal contact at the sur-
face of the die.

source code

(1) software code written in a

form or language meant to be understood by
programmers. Must be translated to object
code in order to run on a computer.

(2) a set of codewords used to represent

messages, such that redundancy is removed,
in order to require less storage space or trans-
mission time.

source coding

the process of mapping sig-

nals onto a finite set of representative signal
vectors referred to as codewords.

source compression

See

source coding

source encoder

a device that substan-

tially reduces the data rate of linearly dig-
itized audio signals by taking advantage of
the psychoacoustic properties of human hear-
ing, eliminating redundant and subjectively
irrelevant information from the output sig-

nal. Transform source encoders work en-
tirely within the frequency domain, while
time-domain source encoders work primar-
ily in the time domain.

Source decoders

reverse the process, using various masking
techniques to simulate the properties of the
original linear data.

source follower

See

common drain

amplifier

source operand

in ALU operations, one

of the input values.

source routing

method of routing packets

in which the entire route through the network
is prepended to the packet. From any node in
the route, the next entry in the source root de-
termines the node to which the packet should
next be forwarded.

source-coupled pair

See

differential

pair

space division multiple access (SDMA)
multiple access technique where the users’
channels are separated into spot-beams with
highly directional or adaptive antennas al-
lowing reuse of time and frequency resources
between users.

Used in conjunction with

FDMA/TDMA/CDMA.

space invariance

a system which a shift

(translation) in the spatial coordinates for all
inputs yields the same output except for an
identical shift. Thus, in two dimensions, for
an input

I (x, y), output O(x, y) and system

S, if

O(x − x

, y − y

) = S{I (x − x

, y − y

)}

for all

, y

) and all inputs I (x, y), the sys-

tem

S is space invariant.

spacer cable

another name for messenger

cable.

SPARC

See

scaled processor architecture

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spark gap

a pressurized high-current

switch using a principle of electric field dis-
ruption to start the electron flow.

sparse equation

when a set of linear si-

multaneous equations has very few nonze-
ros in any row, the system is said to be
sparse. Normally for a system to be con-
sidered sparse, less than 10% of the possible
entries should be nonzero. For large inte-
grated circuits, less than 1% of the possible
entries are nonzero.

sparse matrix

a rectangular array of num-

bers, most of whose elements are zero or null.

sparse vector

in computer instruction

processing, a matrix in which most elements
have such small values that are treated as ze-
ros. Special representation schemes can be
used to save memory space, with a cost of
increased execution time to access single el-
ements of the matrix.

spatial coherence

See

coherence

spatial dispersion

occurs in a medium

when its dielectric function depends on the
wave number.

spatial domain

the representation of a

signal, usually an image, as a function of spa-
tial coordinates. See also

frequency domain

spatial filtering

a technique used to either

filter out interfering signals in a communica-
tion system, or as a multiple access technique
that enables two or more subscribers, con-
trolled by the same base station to use the
same time, frequency and code resources on
the grounds of their physical location or spa-
tial separation. See also

beamforming

spatial frequency

the variables of the 2-

D Fourier transform of a function of spatial
coordinates are referred to as horizontal and
vertical spatial frequencies. The spatial fre-
quency of a 2-D sinusoidal signal in a given

dimension is the number of cycles per unit
distance in that dimension.

spatial hole burning

spatially localized

reduction in the gain of a laser amplifier due
to saturation by an intense signal; transverse
spatial hole burning due to the transverse
beam profile is distinguished from longitudi-
nal spatial hole-burning due to the standing
wave nature of the fields and possibly also
to high gain per pass; spatial relaxation (or
cross-relaxation) reduces spatial hole burn-
ing.

spatial light modulator (SLM)

a device

that alters both the spatial and temporal char-
acter of a light beam. A three-port device
with input, readout, and control or modula-
tion ports. Modulation signals can be ap-
plied either electrically, i.e., an electrically
addressed spatial light modulator, or opti-
cally, i.e., optically addressed spatial light
modulator. Also called a light valve.

spatial light modulator in optical comput-
ing

a device for modulating amplitude or

phase of light passing through it. If the input
signal is a light beam, it is called optically ad-
dressed spatial light modulator. If the input
signal is electronic, it is called electrically ad-
dressed spatial light modulator. Light mod-
ulation is usually based on the electro-optic
effect. In optical computing, an optically ad-
dressed spatial light modulator is a device
used as a medium for controlling or switching
light using light. Since a light beam cannot
directly affect another light beam, a spatial
light modulator is required. The modulation
process can be seen, first, as the modulat-
ing light affecting the spatial light modula-
tor; then the affected spatial light modulator
modulates another light beam.

spatial locality

See

locality

spatial power combining

the power gen-

erated from many devices can be combined
coherently into space. These techniques are

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