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Electrical Engineering Dictionary - part 77

G (giga)

a prefix indicating a quantity of

. For instance, a gigabyte (GB) of storage

is 1

,000,000,000 (typically implemented as

0) bytes.

common notation for compression.

See

compression

common notation for DC drain con-

ductance.

common notation for current gain. G

is dimensionless.

common notation for DC transconduc-

tance.

common notation for power gain in

decibels.

common notation for transducer gain

in amperes/volt.

common notation for voltage gain.

is dimensionless.

G-line

a line of the mercury spectrum cor-

responding to a wavelength of about 436 nm.

GaAlSb/InGaAlAsSb

nearly lattice

matched semiconductor heterostructure sys-
tem capable of “staggered” band lineups in
which the electrons and holes congregate in
separate layers.

Unique transport proper-

ties are utilized in optical devices and tunnel
structures.

GaAs

periodic table symbol for gallium

arsenide. See

gallium arsenide

GaAs laser

a semiconductor laser for

wavelengths in the near infrared. The active

medium is a gallium-arsenide semiconductor
alloy.

GaAs/AlGaAs

most commonly grown

semiconductor epitaxial heterostructure due
to its lattice match, common anion, and ex-
isting technology base of GaAs devices.

Gabor transform

a short-time Fourier

transform in which the window function is
the Gaussian function.

gain

(1) the ratio of the output variable of

a device to its input variable. For calculation
purposes, the dimensionality of the gain is
simply the unit of the output variable divided
by the unit of the input variable. The gain of
a device is a dimensionless value only when
the electrical units of both the input and out-
put variables are the same (e.g., voltage gain,
current gain, power gain, etc.). In this case,
a gain greater than one indicates an increase
from input to output, while a value for gain
less than one is indicative of a decrease (or
attenuation). The overall gain of several cas-
caded components is found by multiplying
the individual gains of each component in the
system. Gain is often expressed in decibels
to facilitate calculation of cascaded gains in
a system. See also

decibel

(2) the ratio of the radiation intensity of

a particular antenna to that of an isotropic
radiator, in the same direction and at the same
distance.

gain circles

circles of constant gain plot-

ted on the Smith chart that can be used to
graphically impedance match a device to
achieve a desired gain. The circles are gener-
ated by plotting on the Smith chart the solu-
tion for the source reflection coefficient,

or load reflection coefficient,

, in the trans-

ducer gain equation for a fixed value of

G =

−|0

|(1−S

)(1−S

)−S

2000 by CRC Press LLC

for a fixed value of

, where

and

are the scattering parameters for the

device.

gain coefficient

factor multiplying dis-

tance in a formula for the exponential am-
plitude or intensity growth of a wave in an
unsaturated amplifying medium.

gain compensation

this deals with the

assumption in motion estimation in inter-
frame coding that illumination is spatially
and temporally uniform.

Under these as-

sumptions, the monochrome intensities

b(zt)

and

b(zt − τ) of two consecutive frames are

related by

b(zt) and b(z − D, t − τ) where τ

is the time between two frames, D is the two-
dimensional translation vector. Often this as-
sumption about uniform illumination is not
correct. In some situations, a multiplicative
factor called gain is used to change the inten-
sity. This is called gain compensation. This
results in estimating D using gradient-type
algorithms to minimize the square of the pre-
diction error.

gain focusing

focusing or collimation of

an electromagnetic beam by the profile of the
gain; gain guiding.

gain guided laser diode

electrically

pumped semiconductor laser in which the
mode fields are confined in the transverse di-
rection by the profile of the gain.

gain medium

medium for which an out-

put electromagnetic wave has more power
than the corresponding input, essential for
laser operation.

gain ripple

difference between the

maximum gain (

max

= 10 log

[

outmax

incident

]

) and the minimum gain across the

band (

min

= 10 log

[

outmin

incident

]

expressed in decibels. The band edges are
usually defined as the highest and lowest fre-
quencies within a contiguous band of inter-
est at which the gain equals the minimum

required passband gain.

ripple

= G

max

− G

min

= 10 log

outmax

incident

− 10 log

outmin

incident

gain saturation

reduction in gain that oc-

curs when the intensity of a laser field de-
pletes the population inversion.

gain switching

rapid turn-on of the gain in

a laser oscillator for the purpose of producing
a large output pulse.

gain–bandwidth product

for amplifiers

based on a voltage-feedback op-amp, in-
creasing the closed-loop gain causes a pro-
portional decrease to the closed-loop band-
width; thus the product of the two is a con-
stant.

This constant is called the gain–

bandwidth product, and is a useful figure-of-
merit for the performance of the op-amp.

gain-guided laser

laser in which the mode

fields are confined in the transverse direction
by the profile of the gain.

gain-shape vector quantization (GSVQ)

See

shape-gain vector quantization

gain-transfer measurement method
common antenna gain measurement scheme
in which the absolute gain of the antenna un-
der test is determined by measuring its gain
relative to a gain standard (i.e., antenna with
accurately known gain).

GaInN/AlInN

rapidly evolving semicon-

ductor heterostructure system with ability to
emit light in the green and blue regions of the
spectrum for long-lifetime LEDs and lasers.

Galerkin’s method

in an integral equa-

tion technique used to solve a numerical elec-
tromagnetic problem, the method in which
the expansion and testing functions are the
same.

2000 by CRC Press LLC

gallium arsenide (GaAs)

a composite

widely used in the fabrication of active el-
ements.

gallium phosphide (GaP)

(1) a semicon-

ductor for high-speed electronics and that is
part of the family of III-V compounds for
semiconductor lasers.

(2) an acousto-optic material with good

acousto-optic figure of merit and with
low acoustic attenuation for high-bandwidth
acousto-optic cells.

galloping

a low-frequency vibration of

electric power lines caused by wind.

Galois field

a finite field with

q elements

denoted as GF

(q), important in the study of

cyclic codes. See also

finite field

Galvani, Luigi

(1737–1798)

Born: Bologna, Italy

Galvani is best known for the use of

his name in the description of zinc plating,
or “galvanizing” metals.

Galvani was an

anatomist who studied the flow of electric-
ity in frog’s legs when metal contacts were
applied. Many of Galvani’s ideas were later
proved incorrect by Alessandro Volta. How-
ever, his pioneering work was honored by
the reference to Galvanic current as an early
name for electric current.

Andre Ampere

also honored him by naming his current mea-
surement apparatus a galvanometer.

gamma camera

a device that uses a scin-

tillation crystal to detect gamma photons for
radionuclide imaging. Also known as a scin-
tillation camera.

gamma correction

inside a CRT, the lu-

minance of a pixel is represented by a volt-
age

V ; however, the luminance of the ray

produced by that voltage is not proportional
to

V , but rather to V

, where

γ is a device-

dependent constant between 2 and 2

.5. It is

thus necessary to compensate for this effect
by transforming the luminance

L into L

/γ

;

this is called gamma correction. Some CCD

cameras implement gamma correction di-
rectly on the signal that they generate. Some
computer monitors allow modification of the
factor

γ or gamma correction through soft-

ware.

gamma rays

electromagnetic radiation of

very high energy (greater than 30 keV) emit-
ted after nuclear reactions or by a radioactive
atom when its nucleus is left in an excited
state after emission of alpha or beta particles.

gamma-ray laser

laser producing its out-

put in the gamma-ray region of the spectrum,
often considered to be any wavelength below
about 0.1 angstrom; graser, not yet demon-
strated.

ganged

operation of a multiple phase de-

vice with all phases operated simultaneously.

GaP

See

gallium phosphide

gap filler

a low-power transmitter that

boosts the strength of transmitted DAB RF
signals in areas that normally would be shad-
owed due to terrain obstruction. Gap fillers
can operate on the same frequency as DAB
transmissions or on alternate channels that
can be located by DAB receivers using auto-
matic switching.

gapless arrester

a lightning arrester

which is distinguished from a gapped arrester
by having a continuous conductive path be-
tween the conductor and ground.

gapped arrester

a lightning arrester

whose conducting path contains a gas- or air-
filled spark gap which must be broken down
by the lightning impulse voltage.

garbage

an object or a set of objects that

can no longer be accessed, typically because
all pointers that direct accesses to the object
or set have been eliminated.

garbage collection

the process by which

the memory, a program no longer uses, is

2000 by CRC Press LLC

automatically reclaimed and reused. Rely-
ing on garbage collection to manage mem-
ory simplifies the interfaces between pro-
gram components. Two main methods used
to implement garbage collection are refer-
ence counting and mark-and-sweep.

garbage collector

a software run-time

system component that periodically scans
dynamically allocated storage and reclaims
allocated storage that is no longer in use
(garbage).

gas cable

an electric power cable which

is pressurized with an insulating gas, typi-
cally sulfur hexaflouride, for its primary in-
sulation.

gas capacitor

a capacitor whose dielec-

tric is composed of a high-pressure gas, of-
ten nitrogen or an electronegative gas such as
sulfur hexaflouride.

gas circuit breaker

a circuit breaker in

which the arc between the contacts is extin-
guished by immersion in or a blast of an elec-
tronegative gas.

gas discharge excitation

electron impact

excitation or pumping of a laser medium oc-
curring as a result of collisions between the
lasing atoms or molecules and the discharge
electrons.

gas dynamic excitation

excitation or

pumping of a laser medium occurring as a re-
sult of heating followed by rapid expansion
and cooling of a gaseous laser medium.

gas insulated switchgear

circuit break-

ers and switches whose primary insulation is
compressed gas.

gas laser

laser in which the amplifying

medium is a gas.

gas metal arc welding (GMAW)

a weld-

ing process that produces coalescence of met-
als by heating them with an arc between

a consumable filler metal electrode and the
parts to be joined. The process is used with
shielding gas and without the application of
pressure.

gas substation

an electric power substa-

tion in which the conductors are insulated
from each other and the ground by a high-
pressure gas, generally sulfur hexaflouride.

gas tungsten arc welding (GTAW)

welding process that produces coalescence of
metals by heating them with an arc between
a nonconsumable tungsten electrode and the
parts to be joined. The process is used with
shielding gas and without the application of
pressure. Filler may or may not be used.

gate

(1) a logical or physical entity

that performs one logical operation, such as
AND, NOT, or OR.

(2) the terminal of a FET to which controls

the flow of electrons from source to drain. It
is usually considered to be the metal contact
at the surface of the die. The gate is usually
so thin and narrow that if any appreciable
current is allowed to flow, it will rapidly heat
up and self-destruct due to I-R loss. This
same resistance is a continuing problem in
low noise devices, and has resulted in the cre-
ation of numerous methods to alter the gate
structure and reduce this effect.

gate array

a semicustom integrated cir-

cuit (IC) consisting of a regular arrangement
of gates that are interconnected through one
or more layers of metal to provide custom
functions.

Generally, gate arrays are pre-

processed up to the first interconnect level
so they can be quickly processed with final
metal to meet customer’s specified function.

gate length

the length in microns of that

portion of the FET channel, as measured in
the direction of channel current flow, that can
be pinched off by application of the proper
control bias. Gate lengths are usually on the
order of 0.1 to 2 microns. The

max

of a FET

is inversely proportional to the gate length.

2000 by CRC Press LLC

Content .. 75 76 77 78 ..