Page 259 - Electrical Engineering Dictionary

set S, the entropy, H(X) is defined as ble sideband AM waveform, e(t), is a scaled
representation of the intelligence.
X
H(X) =− p(x) log p(x)
x∈S
envelope delay the time it takes for a
Also written H(p), emphasizing the sole de- specific reference point on the envelope of
pendence upon the mass function. See also a modulated wave to propagate between two
differential entropy, relative entropy, mutual points in a circuit or transmission system. In
information. a time invariant system, the envelope delay is
the derivative (i.e., rate of change) of phase
entropy coding a term generally used as (in radians) with respect to angular frequency
equivalent to lossless source coding. The (also in radians) as the envelope of the sig-
name comes from the fact that lossless source nal passes between two points in the system.
coding can compress data at a rate arbitrarily Also referred to as time delay.
close to the entropy of the source.
envelope detection a device that produces
entropy estimation noiseless source cod-
an output waveform that is proportional to
ing theorem states that the bit rate can be
the real envelope of its input, i.e., when the
made arbitrarily close to the entropy of the input is A(t)cos(2πf c t + θ(t), the output is
source that generated the image. Entropy es- v(t) = CA(t) with C a constant.
timation is the process of characterizing the
source using a certain model and then find-
envelope detector the optimum structure
ing the entropy with respect to that model.
for detecting a modulated sinusoid with ran-
The major challenge here is to approximate
dom phase in the presence of additive white
the source structure as close as possible while
Gaussian noise.
keeping the complexity of the model and the
number of parameters to a minimum.
environment a set of objects outside the
system, a change in whose attributes affects,
entry mask bit pattern associated with a
and is affected by, the behavior of the system.
subroutine entry point to define which pro-
cessor registers will be used within the sub-
routine and, therefore, which should be saved environmental dispatch a generation
upon entry to the subroutine. Some proces- scheme in which units are committed so as
sor designs perform this state saving during to minimize disturbance to the natural envi-
the execution of the instruction that calls a ronment.
subroutine.
epipolarline instereovision, theintersec-
entry point instruction that is the first in- tion of an image plane with an epipolar plane,
struction in a subroutine. which is the plane identified by a point P and
the centers of projection of the two cameras.
ENV See equivalent noise voltage.
epitaxial layer a doped layer of semi-
envelope the imaginary waveform pro-
conducting material grown on the surface of
duced by connecting the peak values of a
a prepared semiconductor substrate. Vari-
modulated carrier wave. For AM, the am-
ous methods are utilized, resulting in a very
plitude of the carrier sinusoid is a function of
thin and dimensionally well controlled active
time
layer for fabricating semiconductor devices.
e(t) = E(t) sin(ω c + θ)
“Epi” parts generally are more uniform and
where E(t) is a function of the intelligence. perform better than ion implanted devices,
In this case, the envelope of the resulting dou- but are also more expensive to fabricate.

c
2000 by CRC Press LLC