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Electrical Engineering Dictionary - part 63

set

S, the entropy, H (X) is defined as

H (X) = −

x∈

p(x) log p(x)

Also written

H (p), emphasizing the sole de-

pendence upon the mass function. See also

entropy coding

a term generally used as

equivalent to lossless source coding. The
name comes from the fact that lossless source
coding can compress data at a rate arbitrarily
close to the entropy of the source.

entropy estimation

noiseless source cod-

ing theorem states that the bit rate can be
made arbitrarily close to the entropy of the
source that generated the image. Entropy es-
timation is the process of characterizing the
source using a certain model and then find-
ing the entropy with respect to that model.
The major challenge here is to approximate
the source structure as close as possible while
keeping the complexity of the model and the
number of parameters to a minimum.

entry mask

bit pattern associated with a

subroutine entry point to define which pro-
cessor registers will be used within the sub-
routine and, therefore, which should be saved
upon entry to the subroutine. Some proces-
sor designs perform this state saving during
the execution of the instruction that calls a
subroutine.

entry point

instruction that is the first in-

struction in a subroutine.

ENV

See

equivalent noise voltage

envelope

the imaginary waveform pro-

duced by connecting the peak values of a
modulated carrier wave. For AM, the am-
plitude of the carrier sinusoid is a function of
time

e(t) = E(t) sin(ω

+ θ)

where

E(t) is a function of the intelligence.

In this case, the envelope of the resulting dou-

ble sideband AM waveform,

e(t), is a scaled

representation of the intelligence.

envelope delay

the time it takes for a

specific reference point on the envelope of
a modulated wave to propagate between two
points in a circuit or transmission system. In
a time invariant system, the envelope delay is
the derivative (i.e., rate of change) of phase
(in radians) with respect to angular frequency
(also in radians) as the envelope of the sig-
nal passes between two points in the system.
Also referred to as time delay.

envelope detection

a device that produces

an output waveform that is proportional to
the real envelope of its input, i.e., when the
input is

A(t)cos(2πf

t + θ(t), the output is

v(t) = CA(t) with C a constant.

envelope detector

the optimum structure

for detecting a modulated sinusoid with ran-
dom phase in the presence of additive white
Gaussian noise.

environment

a set of objects outside the

system, a change in whose attributes affects,
and is affected by, the behavior of the system.

environmental dispatch

a generation

scheme in which units are committed so as
to minimize disturbance to the natural envi-
ronment.

epipolar line

in stereo vision, the intersec-

tion of an image plane with an epipolar plane,
which is the plane identified by a point

P and

the centers of projection of the two cameras.

epitaxial layer

a doped layer of semi-

conducting material grown on the surface of
a prepared semiconductor substrate. Vari-
ous methods are utilized, resulting in a very
thin and dimensionally well controlled active
layer for fabricating semiconductor devices.
“Epi” parts generally are more uniform and
perform better than ion implanted devices,
but are also more expensive to fabricate.

2000 by CRC Press LLC

EPROM

See

erasable programmable

read-only memory

equal area criterion

a criterion used of-

ten in power system studies whenever the
stability of a single machine system needs
to be determined without actually solving
the swing equation. It is a direct approach.
See also

electromechanical equation

swing

equation

equal gain combining

a method of di-

versity combining in which the outputs of
several communication channels are first co-
phased and then summed. The resulting sig-
nal has increased mean power and reduced
fade depth. See also

angle diversity

antenna

diversity

equal ripple

in-band power gain or power

loss vs. frequency response in which the min-
imum dips are equal in power and maximum
peaks are equal in power.

equalization

a method used in communi-

cation systems to compensate for the channel
distortion introduced during signal transmis-
sion.

equalizer

a device used at the receiver

(typically a digital filter) that attempts to sup-
press or cancel intersymbol interference.

equalizer adaptive

an equalizer that auto-

matically adjusts its parameters to suppress
or cancel intersymbol interference. In the
case of a digital filter, the parameters are the
filter coefficients, which are adapted to min-
imize a cost criterion (e.g., mean-squared er-
ror).

equalizer decision-feedback

a nonlinear

digital filter that consists of a linear prefilter
P (z) for suppressing precursor intersymbol
interference, and a feedback filter

F (z) for

suppressing postcursor intersymbol interfer-
ence.

equalizer minimum mean squared error

(MMSE)

a digital equalizer (filter) in

which the coefficients are selected to min-
imize the mean-squared error between the
transmitted symbols and the filter outputs.

equalizer transversal

an equalizer that is

implemented as a finite impulse response dig-
ital filter. Also called a “tapped-delay line.”

equalizer zero-forcing

an equalizer in

which the parameters are adjusted to elimi-
nate intersymbol interference (at the expense
of enhancing the noise).

equalizing pulse interval

series of 12

sync pulses inserted in the vertical blank-
ing interval of each field of the NTSC com-
posite video signal. The equalizing pulse
makes a transition between the composite
signal blanking level and the sync level at
one-half horizontal line intervals. The dura-
tion at the sync level is 3.575

± 0.425 percent

of the horizontal line time (0.45 to 0.5 times
the horizontal sync). There are three hor-
izontal lines of equalizing pulses (6 pulses)
preceding the vertical synchronization signal
and 3 horizontal lines of equalizing pulses (6
pulses) following the vertical synchroniza-
tion interval. The equalizing pulse interval
repeats every field of 262.5 horizontal lines.

equalizing pulses

in an encoded video

signal, a series of 2

× line frequency pulses

occurring during vertical blanking, before
and after the vertical synchronizing pulse.
Different numbers of equalizing pulses are
inserted into different fields to ensure that
each field begins and ends at the right time
to produce proper interlace. The 2

× line rate

also serves to maintain horizontal synchro-
nization during vertical blanking.

equiband

a complex method of chromi-

nance signal demodulation, that does not re-
quire dissimilar filters and delay equilization;
it most frequently utilizes a bandwidth of 800
KHz.

2000 by CRC Press LLC

equilibrium manifold

See

sliding surface

equilibrium point

for a continuous-time

system

dx/dt = f (t, x), a constant solution

∗

such that

f (t, x

∗

) = 0. For a discrete-

time system

x(k + 1) = f (k, x(k)), a con-

stant solution

∗

such that

∗

= f (k, x

∗

equilibrium solution

consider a dynamic

system described by a first-order vector dif-
ferential equation of the form

˙x(t) = f (x(t), t, u(t))

If there exists a vector

such that

f (x

, t, 0) = 0

∀t

then whenever

x(t) = x

, the system is said

to be in equilibrium and

is called an equi-

librium state.

equilibrium state

See

equilibrium solution

equipment hazard

a possible source of

peril, danger, risk, or difficulty.

equiripple filter

a filter designed using an

iterative algorithm, for example, Remez ex-
change algorithm, to minimize the maximal
deviation from the desired magnitude fre-
quency response in both passband and stop-
band for a given filter length. It has equal
amplitude ripples within the passband and
stopband. See also

Chebyshev filter

equivalence in continuous-valued logic
similar to equivalence in conventional logic
equivalence in continuous-valued logic be-
tween two variables

x and y, which are con-

tinuous in the open interval

(0, 1), can be de-

fined as

e(x, y) =

max

{min(x, y), min((1 − x), (1 − y))} .

See

equivalence in logic

equivalence in logic

for two Boolean vari-

ables

x and y, defined as

(x ≡ y) = ( ¯x ∧ ¯y) ∨ (x ∧ y)

equivalence theorem

an electromagnetic

theorem: If the tangential magnetic and elec-
tric fields are known everywhere on some
closed surface

S, then these fields may be re-

placed with equivalent electric and magnetic
surface currents, respectively. These equiv-
alent currents will produce the same field
structure exterior to

S as the original fields

and the null field internal to

equivalent circuit

a combination of elec-

tric circuit elements chosen to represent the
performance of a machine or device by es-
tablishing the same relationships for voltage,
current, and power.

equivalent control

an algorithm used

to determine a system’s dynamics when re-
stricted to a sliding surface.

The method

entails combining the solution to an alge-
braic equation involving the time derivative
of the function describing the sliding surface
and the dynamical system’s model. See also

variable structure system

and

sliding mode

control

equivalent current

a theoretical current

used to obtain the scattered field from a sur-
face or discontinuity. The equivalent current
is formulated to represent the actual physi-
cal currents so as to result in an equivalent
scattered field.

equivalent impedance

the impedance of

the windings of an electromagnetic machine
reflected to one side (component) of the ma-
chine. For example, in a transformer, the
equivalent impedance consists of the com-
bined leakage reactances and resistances of
the primary and secondary.

equivalent noise current (ENI)

a noise

current source that is effectively in paral-
lel with either the noninverting input termi-

2000 by CRC Press LLC

nal (ENI

) or the inverting input terminal

(ENI

−

) and represents the total noise con-

tributed by the op amp if either input terminal
is open circuited.

equivalent noise temperature

an alter-

native way of describing the noise properties
of two port networks.

equivalent noise voltage (ENV)

a noise

voltage source that is effectively in series
with either the inverting or noninverting in-
put terminal of the op amp and represents the
total noise contributed by the op amp if the
inputs were shorted.

equivalent reactance

the reactance of the

windings of an electromagnetic machine re-
flected to one side (component) of the ma-
chine. See also

equivalent impedance

equivalent resistance

the resistance of the

windings of an electromagnetic machine re-
flected to one side (component) of the ma-
chine. See also

equivalent impedance

equivalent source

fictitious source used

in the equivalence theorem.

equivalent sphere illumination (ESI)

the

level of sphere illumination that would pro-
duce task visibility equivalent to that pro-
duced by a specific lighting environment.

equivalent system dynamics

a dynamical

system model resulting from substituting the
equivalent control into the plant’s modeling
equation. The equivalent system’s trajectory
is confined to a surface that is parallel to the
sliding surface if the system’s initial condi-
tion is off the sliding surface. If the initial
condition is on the sliding surface, then the
equivalent system’s trajectory will stay on the
sliding surface.

erasable optical disk

a magneto-optical

disk that can be both read/written and
erased. A thermo-magneto process is used
for recording and erasure of information.

The recording process uses e.g., the “laser
power modulation” or the “magnetic field
modulation” technique.

erasable programmable read-only mem-
ory (EPROM)

a nonvolatile chip mem-

ory, it is used in the place of PROM. EPROMs
presents a glass on the case that allows one
to see the chip. They can be erased by ex-
posing the chip at the ultraviolet light for
typically 20 minutes. Once erased they can
be reprogrammed.

The programming has

to be performed by using a special algo-
rithm and a supplementary

. Also called

UVPROM. See also

electronically erasable

programmable read-only memory

erasure

in a forward error control sys-

tem, a position in the demodulated sequence
where the symbol value is unknown. De-
pending on the quality of the received signal
when no decision is made on a particular bit,
the demodulator inserts an erasure in the de-
modulated data. Using the redundancy in the
transmitted data, the decoder attempts to fill
in the positions where erasures occurred. See

binary erase channel

erbium doped fiber amplifier (EDFA)
an optical amplifier based on the rare-earth
erbium that can amplify optical signals in
the 1550 nm telecommunications window.
The useful gain region extends from approx-
imately 1530 nm to 1565 nm.

EREW

See

exclusive reads and exclusive

writes

ergodic process

a process that has all pos-

sible ergodic properties.

For process

X(t) when the time average

lim

T →∞

(1/T )