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Electrical Engineering Dictionary - part 17

cross section, or balanced with respect to vir-
tual ground. Balanced wiring configurations
are often used to prevent noise problems such
as ground loops. Contrast with

unbalanced

line

balanced load

a load on a multi-phase

power line in which each line conductor sees
the same impedance.

balanced mixer

a nonlinear 3-port device

(two inputs, one output) used to translate an
input signal’s frequency component either up
or down the frequency spectrum by generat-
ing the sum and difference of two or more
frequencies present at its inputs. The three
ports are termed RF (radio frequency), LO
(local oscillator), and IF (intermediate fre-
quency).

A balanced mixer translates the

frequency components found in the RF in-
put signal to the IF output in such a manner
as to minimize the amount of LO noise arriv-
ing at the IF. This reduces the mixer’s over-
all noise figure and increases its sensitivity.
Other advantages of these mixers include im-
proved local oscillator isolation and linearity
and higher power handling ability.

balanced modulator

a modulator in

which the carrier and modulating signal are
introduced so that the output contains the two
sidebands without the carrier.

balanced operation

n-phase circuits

(n > 1), an operating condition in which the
voltages (currents) of the phases are equal-
amplitude sinusoids with phase-angles dis-
placed by a specific angle

φ. The angle (φ)

is a function of the number of phases (n). For
n = 2, φ = 90 degrees, for n = 3, φ = 120
degrees. In machine analysis the term “bal-
anced” is also used to describe a machine that
has symmetrical phase windings.

balanced slope detector

an arrangement

of two detectors designed to convert an FM
signal to AM for detection. This is accom-
plished by setting the IF center frequency
so that it falls on the most linear portion

of the response curve. Frequency changes
(FM) will result in corresponding amplitude
changes that are then sent to an AM detector.
The balanced version is two slope detectors
connected in parallel and 180 degrees out of
phase.

ball grid array (BGA)

a modern high

I/O count packaging method. It reduces the
package size and its pin-to-pin trace gap in
order to integrate more functions and relia-
bility in a single space. It can have as many as
324 pins. BGA sockets are high speed, high
reliability, surface-mountable, and can be in-
stalled without soldering. The related terms
are PBGA—plastic ball grid array, CBGA—
ceramic ball grid array, TBGA—tape auto-
mated bonded ball grid array. The disadvan-
tage of BGA packaging is that new tools and
skills are required to mount or replace the
chipset manually for repair purposes.

ballast

a starting and control mecha-

nism for fluorescent and other types of gas-
discharge lamps. Initially a ballast supplies
the necessary starting (or striking) voltage in
order to ionize the gas to establish an arc be-
tween the two filaments in the lamp. Once the
gas is ionized, the ballast controls the input
power and thus the light output to maximize
the efficiency and life of the lamp.

balun

a network for the transformation

from an unbalanced transmission line, sys-
tem or device to a balanced line, system or
device. Baluns are also used for impedance
transformation. Derived from “balanced to
unbalanced.”

In antenna systems, baluns are used to

connect dipole-type antennas to coaxial ca-
ble, to balance the current on dipole arma-
tures, and to prevent currents from exciting
the external surface of the coaxial shield.

See also

balanced

unbalanced line.

band

reference name for a range of fre-

quencies. Current defined bands include the
following.

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Band Name

Reference Range

L-band

1.12 - 1.7 GHz

8.2 - 12.4 GHz

12.4 - 18 GHz

26.5 - 40 GHz

50 - 75 GHz

75 - 110 GHz

band gap

the energetic gap between the

conduction and valence band edges of a ma-
terial (usually referred to semiconductors).

band stop filter

filter that exhibits fre-

quency selective characteristic such that fre-
quency components of an input signals pass
through unattenuated from input to output ex-
cept for those frequency components coinci-
dent with the filter stop-band region, which
are attenuated. The stop-band region of the
filter is defined as a frequency interval over
which frequency components of the input
signal are attenuated.

band structure

the energy versus mo-

mentum relationship for an electron in a pe-
riodic crystal.

band-limited signal

a signal

x(t) is said to

be band limited if its Fourier transform

X(ω)

is zero for all frequencies

ω > ω

, where

is called the cutoff frequency.

band-pass filter

(1) a circuit whose trans-

fer function, or frequency response,

H (ω) is

zero or is very small for frequencies not in a
specified frequency band. In a strict sense
H (ω) = 0 for |ω| 6∈ [ω

, ω

] for some

< ω

Compare with

(2) an electronic or electrical circuit which

has the response shown in the figure below.
There are two cut-off frequencies,

and

. In the passband

< ω < ω

| N(jω) |

is constant. In the stopbands,

ω < ω

and

ω > ω

| N(jω) | is very small and there

is practically no transmission of the signal.

Band-pass filter response.

band-pass network

a configuration of

solely passive components or combination of
active and passive components that will at-
tenuate all signals outside of the desired range
of frequency.

band-pass signal

a signal whose Fourier

transform or spectrum approaches zero out-
side a given frequency band.

Ideally, the

spectrum should equal zero outside the band,
but this is difficult to achieve in practice. This
may be described mathematically as follows:
let

X(ω) be the Fourier transform of the sig-

nal. Then, for a band-pass signal we have
X(ω) = 0 for |ω| 6∈ [ω

, ω

], for some

< ω

band-reject filter

See

band-stop filter

band-stop filter

a filter which attenu-

ates only within a finite frequency band and
leaves the signal unaffected outside this band.
See also

band-pass filter

high-pass filter

low-pass filter

bandgap energy

in materials with band

energy levels, the minimum energy needed
to excite a charge carrier from a lower to an
upper band. See also

absorption edge

bandgap engineering

in materials such

as compound semiconductors and superlat-
tice structures, the fabrication of materials
with specific bandgap energies by varying the
fractional proportions of the constituents and
by varying superlattice layer thicknesses.

bandgap narrowing

reduction of the for-

bidden energy gap of a semiconducting ma-
terial due to the narrowing influence of im-
purities.

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bandgap reference

a voltage reference

based on the 1.205 V bandgap voltage of sil-
icon.

bandgap wavelength

the optical wave-

length corresponding to a photon energy
equal to the bandgap energy.

bandlimited

a waveform is described as

bandlimited if the frequency content of the
signal is constrained to lie within a finite band
of frequencies. This band is often described
by an upper limit, the Nyquist frequency, as-
suming frequencies from DC up to his upper
limit may be present. This concept can be ex-
tended to frequency bands that do not include
DC.

bandwidth

(1) the frequency range of

a message or information processing system
measured in hertz.

(2) width of the spectral region over which

an amplifier (or absorber) has substantial
gain (or loss); sometimes represented more
specifically as, for example, full width at half
maximum.

(3) the property of a control system or

component describing the limits of sinu-
soidal input frequencies to which the sys-
tem/component will respond. It is usually
measured at the half-power points, which are
the upper and lower frequencies at which the
output power is reduced by one half. Band-
width is one measure of the frequency re-
sponse of a system, i.e., the manner in which
it performs when sine waves are applied to
the input.

(4) the lowest frequency at which the ra-

tio of the output power to the input power
of an optical fiber transmission system de-
creases by one half (3 dB) compared to the
ratio measured at approximately zero mod-
ulation frequency of the input optical power
source. Since signal distortion in an opti-
cal fiber increases with distance in an opti-
cal fiber, the bandwidth is also a function of
length and is usually given as the bandwidth-
distance product for the optical fiber in mega-

hertz per kilometer. See also

bandwidth-distance product

bandwidth efficiency

the ratio of the

information rate in bits per second to the
required bandwidth in hertz for any digital
modulation technique.

bandwidth improvement (BI)

a dB read-

ing that is a comparison of the RF bandwidth
of a receiver to the IF bandwidth. Designated
as BI, it is 10 log

bandwidth-distance product

a measure

of the information carrying capacity of an op-
tical fiber which emphasizes that the band-
width is a function of distance. For example,
an optical fiber with a specification of 500
MHz-km bandwidth-distance product would
have a 500 MHz bandwidth over 1 km, a
50 MHz bandwidth over 10 km or a 1 GHz
bandwidth over 0.5 km. See also

bandwidth

optical fiber

bang-bang control

control action

achieved by a command to the actuator that
tells it to operate in either one direction or the
other at any time with maximum energy.

Bang-bang control is an optimal or subop-

timal piecewise constant control whose val-
ues are defined by bounds imposed on the am-
plitude of control components. The control
changes its values according to the switching
function which may be found using Pontrya-
gin maximum principle. The discontinuity
of the bang-bang control leads to disconti-
nuity of a value function for the considered
optimal control problem. Typical problems
with bang-bang optimal control include time-
optimal control for linear and bilinear control
systems.

Bardeen, John

(1908–1991) Born:

Madison, Wisconsin, U.S.A.

Bardeen is best known for his two Nobel

Prizes. The first prize he received was in
1956 for his development at Bell Labs, along
with Walter Brattain and William Schockley,
of the first transistor. When the three applied

2000 by CRC Press LLC

for a patent for the device in 1948 they called
it a germanium transfer resistance unit; hence
the name transistor. This device was a sig-
nificant step in the development of integrated
circuits. Bardeen’s second Nobel, which he
shared with Leon Cooper and John R. Schri-
effer, was for his work at the University of
Illinois in describing the theory of supercon-
ductivity.

bare-hand

refers to a method of servic-

ing energized overhead conductors in which
the line worker’s body is maintained at the
same potential as the conductor on which he
is working, thus enabling the conductor to be
contacted without danger of shock.

BARITT

barrier injection transit time, a

microwave transit time device that uses injec-
tion over a forward biased barrier and transit
time delay through a reverse biased junction
to produce negative resistance at microwave
frequencies, useful in low power and self-
oscillating mixer applications.

Barkhausen criterion

two conditions

placed on a feedback oscillator necessary for
sustained oscillation. The Barkhausen crite-
rion states

1. The total loop amplitude transmission

factor must be at least unity.

2. The frequency of oscillation will be that

frequency characterized by a total loop phase
transmission factor of

N2π radians. N is ei-

ther zero or an integer. Simply, for sustained
oscillation, a disturbance that makes a com-
plete trip around the feedback loop of the os-
cillator must be returned at least as strong
as the original disturbance and in phase with
that disturbance.

Barkhausen effect

the series of irregular

changes in magnetization that occur when a
magnetic material is subjected to a change in
magnetizing force.

Barkhausen noise

noise arising in mag-

netic read heads because the interlocking
magnetic domains cannot rotate freely in re-

sponse to an applied field. The response to an
external magnetic field is randomly discon-
tinuous as domains “stick,” and then release.
Barkhausen noise is particularly important in
very small heads and thin-film heads where
very few domains are involved; in larger
heads the effects of many domains tend to av-
erage out and Barkhausen noise is relatively
less important.

barrel distortion

a geometric distortion

of a raster display in which vertical lines ap-
pear to bow outward away from the display
center line. The bowing of the vertical lines
increases as the distance from the vertical
center increases. The appearance of these
vertical lines is similar to the staffs of a bar-
rel. Barrel distortion is a result of the over-
correction for pincushion distortion.

barrel shifter

an implementation of a

shifter, which contains log

(max number of

bits shifted) stages, where each stage shifts
the input by a different power of two number
of positions. It can be implemented as a com-
binational array with compact layout that can
shift the data by more than one bit using only
one gate. For instance, for a 4-bit word, it
can execute instructions shl, shl2, shl3, and
shl4. This shifter lends itself well to being
pipelined.

barrier layer

layer of deposited glass

adjacent to the inner tube surface to create a
barrier against OH diffusion.

barrier voltage

a voltage that develops

across the junction due to uncovered immo-
bile ions on both sides of the junction. Ions
are uncovered due to the diffusion of carriers
across the junction.

Bartlett window

a triangular window

w[n] of width 2M defined as follows:

w[n] =

/2[1 + cos(πn/M)], −M ≤ n ≤ M

otherwise

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