Content .. 31 32 33 34 ..

Electrical Engineering Dictionary - part 33

load impedance optimized not only for a fun-
damental wave but also for harmonic waves
to improve efficiency. An efficiency of the
class F amplifier is 100% under an ideal con-
dition, where the optimum load impedance
for even harmonic waves is short and that for
odd harmonic waves is open.

class G amplifier

a frequency multiply-

ing or harmonic amplifier biased somewhere
between class A and class C, in which the
input is tuned to the fundamental input fre-
quency and the output is tuned to a frequency
multiple of the input.

class H amplifier

frequency mixing am-

plifier biased somewhere between class A
and class C, in which the inputs are tuned to
the input frequencies and the output is tuned
to either the sum or difference frequency.

class S amplifier

sampling or pulse width

modulation amplifier in which a sampling
circuit (or pulse width modulator), pulse am-
plifier and a low pass filter are cascaded.
The input signal is sampled at a significantly
higher rate than the input frequency (this re-
quires a high frequency sampling signal),
and the original signal is transformed into
a constant amplitude pulse chain in which
the pulse widths are proportional to the orig-
inal signal’s amplitude. The resulting pulse
chain is amplified using any of the highly effi-
cient switching methods desired. The output
is then demodulated using a low pass filter,
replicating the original signal. It is impor-
tant to note that rapid variations in the input
signal amplitude relative to the sampling sig-
nal will cause significant distortion or loss of
information.

classified VQ

See

classified vector

quantization

classified vector quantization (CVQ)
a vector quantization technique where dif-
ferent codebooks are developed based image
edge features. The codebook used to encode
a particular block is determined by a clas-

sifier with differentiating capability between
the types of features. A number of codebooks
are developed each to encode blocks of pix-
els containing specific types of features. See
also

vector quantization

classifier

(1) given a set of patterns of

different classes, a classifier is a system ca-
pable of determining the membership of each
pattern.

(2) a method of assigning an object to one

of a number of predetermined classes.

clean cache block

a cache block (or

“line”) is clean if it is a copy of the informa-
tion stored in memory. A clean block can be
overwritten with another block without any
need to save its state in memory.

clear

(1) to set the value of a storage

location to zero (often used in the context of
flip-flops or latches).

(2) clearing a bit (register) means writing

a zero in a bit (register) location. Opposite to
“set.”

clearing time

the total time required to

melt and clear, and thus totally open, a fuse-
type overcurrent device.

cleaved coupled cavity

semiconductor

laser configuration in which the amplifying
region has been cleaved to introduce a mid-
cavity reflecting boundary; added reflector is
intended to improve mode-selectivity char-
acteristics.

click noise

in a fading channel, the noise

associated with a threshold crossing. In a
fading radio channel situation, the moving
user crosses the standing wave patterns in
the propagation environment. As the user
crosses the minima, the service quality tem-
porarily downgrades and, in analogue sys-
tems, is noticeable as clicking.

climbers

two metal spikes, each of which

is strapped to the inside of a line worker’s
legs, pointing down near the ankle. Plunged

2000 by CRC Press LLC

into the sides of a wooden utility pole, they
provide purchase for the worker to scale the
pole.

clipping

nonlinear distortion that occurs

when the input to an amplifier exceeds the
amplifier’s linear range. The amplifier out-
put saturates at its limit, giving a “clipped”
appearance to the output waveform.

clock

(1) the oscillator circuit that gener-

ates a periodic synchronization signal.

(2) a circuit that produces a series of elec-

trical pulses at regular intervals that can be
used for timing or synchronization purposes.

clock cycle

one complete event of a syn-

chronous system’s timer, including both the
high and low periods.

clock doubling

a technique in which the

processor operates internally at double the
external clock frequency.

clock duty cycle

the percentage of time

that the electronic signal remains in the true
or 1 state.

clock pulse

a digital signal that, via its

rising edge or falling edge, triggers a digi-
tal circuit. Flip-flops and counters typically
require clock pulses to change state.

clock recovery

in synchronous systems,

the act of extracting the system clock signal
from the received sequence of information
symbols. See also

symbol synchronization

clock replacement algorithm

a page re-

placement algorithm described as follows: A
circular list of page entries corresponding to
the pages in the memory is formed. Each en-
try has a use bit which is set to a 1 when the
corresponding page has been referenced. A
pointer identifies a page entry. If the use bit
of the page entry is set to a 1, the use bit is re-
set to a 0 and the pointer advances to the next
entry. The process is repeated until an entry
is found with its use bit already reset, which

identifies the page to be replaced. The pointer
advances to the next page entry for the next
occasion that the algorithm is required. The
word “clock” comes from viewing the pointer
as an arm of a clock. Also known as a first-
in-not-used-first-out replacement algorithm.

clock skew

the phenomenon where differ-

ent parts of the circuit receive the same state
of clock signal at different times because it
travels in wires with different lengths. This
skew of the signals causes a processing ele-
ment to generate an erroneous output. Distri-
bution of the clock by means of optical fibers,
waveguides, a lens, or a hologram, eliminates
clock skew.

clock speed

the rate at which the tim-

ing circuit in a synchronous system generates
timing events.

closed convex set

a set of vectors

C such

that of x

, y ∈ C then λx + (1 − λ)y ∈ C for

all 0

≤ λ ≤ 1.

closed kinematic chain

in vision engi-

neering, a sequence of links which forms a
loop.

closed-loop control

control action achieved

by a closed feedback loop, i.e., by measuring
the degree to which actual system response
conforms to desired system response and ap-
plying the difference to the system input to
drive the system into conformance.

closed-loop DC motor acceleration

the

use of sensors to provide feedback to the mo-
tor control circuit indicating the motor is ac-
tually accelerating before the starting resis-
tors are removed from the armature circuit.
Two popular methods to sense motor accel-
eration are CEMF coils, and current sensing
coils.

closed-loop gain

the gain of an opera-

tional amplifier circuit with negative feed-
back applied (with the negative feedback
loop “closed”).

2000 by CRC Press LLC

closed-loop optimal control

operation

or structure of the controller with the deci-
sion mechanism which, under uncertainty,
uses in the best possible way — with respect
to a given a priori criterion — all informa-
tion available to the controller; in particular,
the closed-loop optimal control takes into ac-
count all future time instants at which new
decisions will be made; the best known ex-
ample of a closed-loop optimal control rule is
the solution of the linear-quadratic-Gaussian
problem (LQG problem).

closed-loop system

any system having

two separate paths inside it. The first path
conducts the signal flow from the input of that
system to the output of that same system. The
second path conducts the signal flow from the
output to the input of the system, thus estab-
lishing a feedback loop for the system. See
the figure below for a general description of a
closed-loop system. The forward and back-

A closed-loop system.

ward signal path construct the closed loop,
which conduct the signal flow from the input
stage to the output stage and then back to the
input stage of that system.

closing

a basic morphological operation.

Given a structuring element

B, the closing

B is the composition of the dilation by B

followed by the erosion by

B; it transforms

X into X • B = (X ⊕ B) B. The closing
by

B is what one calls an algebraic closing;

this means that:

(a) it is a morphological

filter;

(b) it is extensive, in other words it can

only increase an object. See

closing/opening filter

one of an impor-

tant class of morphological filters.

Let

and

ϕ be opening and closing operators re-

spectively. The following operators can be
obtained by composing

γ and ϕ (i.e., by ap-

plying them in succession):

γ ϕ, ϕγ , γ ϕγ ,

and

ϕγ ϕ. These are all morphological fil-

ters, and collectively they are called clos-
ing/opening filters or opening/closing filters.
No further operators can be obtained by com-
posing

γ and ϕ. See

clothes pin

slang for a wood or plastic clip

used to secure a blanket to conductors.

CLT

See

central limit theorem

cluster

a group of data points on a space

or a group of communicating computer ma-
chines. A cluster of computers on a local
network can be installed to provide their ser-
vice as a unique computer. This is frequently
used for building large data storage and Web
servers. In computer disks, a cluster consists
of a fixed number of sectors. Each sector
contains several bytes, for example 512.

cluster analysis

in pattern recognition,

the unsupervised analysis of samples to clus-
ter them into classes based on (a) a distance
metric and (b) a clustering algorithm. Typ-
ical algorithms minimize a cluster criterion
(e.g., representation error) by grouping sam-
ples hierarchically or by iteratively reassign-
ing samples to clusters. The K-means algo-
rithm is an example of the latter. In the case of
2-D measurements, cluster analysis becomes
a method of image segmentation.

clustering

(1) any algorithm that creates

the major clusters from a given set of patterns.

(2) a method of unsupervised learning that

aims to discover useful structure in unlabeled
data by grouping similar patterns.

2000 by CRC Press LLC

See

hierarchical clustering

See also

distance measure

similarity measure

clutter

the name given to background

signals which are currently irrelevant to a de-
tection system; clutter is a form of structured
noise.

CMA

See

constant modulus algorithm

CMAC network

See

cerebellar model

articulation network

CMMR

See

common mode rejection

ratio

CMOS

See

complementary metal oxide

semiconductor

abbreviation for central switching

office.

See

carbon dioxide

laser

See

carbon dioxide laser

co-linear array

a phased array of straight

elements in which the axes of the elements lie
along a common line. The elements are typ-
ically center fed half-wave dipoles or folded
dipoles.

co-occurrence matrix

an array of num-

bers that relates the measured statistical de-
pendency of pixel pairs. Co-occurrence ma-
trices are used in image processing to identify
the textural features of an image.

co-prime polynomials

polynomials that

have no common factors. For example, poly-
nomials

+9s+20) and (s

+7s+6) are co-

prime, while

+5s +6) and (s

+9s +14)

are not, since they have a common

(s + 2)

factor.

co-tunneling

a cooperative process,

whereby electrons can tunnel through two se-
ries connected tunneling barriers. In this pro-
cess, the tunneling of an electron through one
of the barriers causes a self-consistent shift of

potential onto the second barrier, which re-
sults in the immediate inducing of a particle
tunneling through this latter barrier.

coarticulation

the transient process cor-

responding to the utterance of two phonemes.
It is due to the movement of the articulatory
organs between the different positions corre-
sponding to the two phonemes.

coax

See

coaxial cable

coaxial cable

A transmission line formed

by two concentric conductors separated by a
dielectric designed to confine the fields and
their energy in the medium between said con-
ductors. It is often used in applications where
signal interference between the cable and its
surrounds must be kept to a minimum. Also
called coax.

coaxial magnetron

a radial magnetron

where the anode and cathode are gradually
transformed into a coaxial line.

cochannel interference (CCI)

interfer-

ence caused by radio transmitters operating
on the same radio frequency as that of a par-
ticular wanted radio frequency signal.

cochannel interference reduction factor
(CIRF)

a key factor used to design a cel-

lular system to avoid the cochannel interfer-
ence.

cochannel reuse ratio (CRR)

the reuse

ratio between radio communication cells us-
ing the same radio channels.

cochannels

radio channels occupying the

same radio frequency allocation

cochlea

a snail-shaped passage commu-

nicating with the middle ear via the round and
oval window. Its operation consists of trans-
ducing the acoustical vibration to nerve im-
pulses, subsequently processed in the brain.

2000 by CRC Press LLC

Content .. 31 32 33 34 ..