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Electrical Engineering Dictionary - part 21

bipolar memory

memory in which a stor-

age cell is constructed from bipolar junction
transistors. See also

static random access

memory (SRAM)

bipolar neuron

a neuron with a signal

between

−1 and +1.

bipolar transistor

See

bipolar junction

transistor

bipole

DC system with two conductors,

one positive and the other negative polarity.
The rated voltage of a bipole is expressed as
±100 kV, for example.

biquad

an active filter whose transfer

function comprises a ratio of second-order
numerator and denominator polynomials in
the frequency variable.

biquadratic transfer function

a ratio-

nal function that comprises a ratio of second-
order numerator and denominator polynomi-
als in the frequency variable.

bird’s beak

feature seen in cross-

sectional photomicrographs of silicon gate
transistors caused by encroachment of oxide
under the gate.

birefringence

The property of certain

materials to display different values of the
refractive index for different polarizations of
a light beam.

birefringent fiber

optical fiber that

has different speeds of propagation for light
launched along its (two distinct) polarization
axes.

birefringent material

material that can

be described by two or more refractive in-
dices along the directions for principle axes.

birthmark

a stamp on a wooden utility

pole which denotes its manufacturer, date of
manufacture, size, and method of preserva-
tion.

bispectra

computation of the frequency

distribution of the EEG exhibiting nonlinear
behavior.

bispectrum

the Fourier transform of the

triple correlation function. It preserves phase
information and uniquely represents a given
process in the frequency domain. It can be
used to identify different types of nonlinear
system response.

BIST

See

built-in self-test

bistable

pertaining to a device with two

stable states. Examples: bistable multivibra-
tor, flip-flop. See also

bistable system

bistable device

See

bistable

bistable optical device

a device whose

optical transmission can take on two possible
values.

bistable system

an optical system where

the transmission can take on two possible val-
ues. See also

bistable

bistatic scattering

a measure of the rera-

diated power (back-scattered) from an illu-
minated target in the direction other than that
of the illuminating source.

bit

(1) the fundamental unit of informa-

tion representation in a computer, short for
“binary digit” and with two values usually
represented by “0” and “1.” Bits are usu-
ally aggregated into “bytes” (7 or 8 bits) or
“words” (12–60 bits).

A single bit within a word may represent

the coefficient of a power of 2 (in numbers),
a logical TRUE/FALSE quantity (masks and
Boolean quantities), or part of a character or
other compound quantity. In practice, these
uses are often confused and interchanged.

(2) in Information Theory, the unit of in-

formation.

If an event

E occurs with a

probability

P (E), it conveys information of

log

(1/P (E)) binary units or bits. When

a bit (binary digit) has equiprobable 0 and

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1 values, it conveys exactly 1.0 bit (binary
unit) of information; the average information
is usually less than this.

bit allocation

the allocation of bits to sym-

bols with the aim of achieving some compres-
sion of the data. Not all symbols occur with
the same frequency. Bit allocation attempts
to represent frequently occurring symbols
with fewer bits and assign more bits to sym-
bols that rarely appear, subject to a constraint
on the total number of bits available.

this way, the average string requires fewer
bits. The chosen assignment of bits is usu-
ally the one that minimizes the correspond-
ing average coding distortion of the source
over all possible bit assignments that satisfy
the given constraint. Typically sub-sources
with larger variances or energy are allocated
more bits, corresponding to their greater im-
portance. See also

transform coding

bit energy

the energy contained in

an information-bearing signal received at a
communications receiver per information bit.
The power of an information bearing signal
at a communications receiver divided by the
information bit rate of the signal. Usually
denoted by

as in the signal to noise ratio

bit error rate (BER)

the probability of

a single transmitted bit being incorrectly de-
termined upon reception.

bit line

used in, for example, RAM mem-

ory devices (dynamic and static) to connect
all memory cell outputs of one column to-
gether using a shared signal line. In static
RAM, the “bit” line together with its com-
plemented signal “-bit” feeds a “sense ampli-
fier” (differential in this case) at the bottom
of the column serving as a driver to the output
stage. The actual cell driving the bit line (and
-bit) is controlled via an access transistor in
each cell. This transistor is turned on/off by
a “word” line, a signal run across the cells in
each row.

bit parallel

a method to transmit or pro-

cess information in which several bits are
transmitted in parallel. Examples: a bit par-
allel adder with 4-bit data has 8 input ports for
them (plus an initial carry bit); an 8-bit paral-
lel port includes true 8-bit bi-directional data
lines.

bit per second (bps)

measure of trans-

fer rate of a modem or a bus or any digital
communication support. ( See also

baud

and

baud rate

bps and baud are not equivalent

since bps is a low-level measure and media;
thus, it includes the number of bits sent for the
low-level protocol, while baud is typically re-
ferred to a higher level of transmission).

bit period

the time between successive

bits in data transmission or data recording.
At the transmitter (or recorder) the timing is
established by a clock. At the receiver (or
reader) an equivalent clock must be recovered
from the bit stream.

bit plane

the binary

N ×N image formed

by selecting the same bit position of the pix-
els when the pixels of an

N × N image are

represented using

k bits.

bit plane encoding

lossless binary en-

coding of the bit planes is termed bit plane
encoding. The image is decomposed into a
set of

k, N × N bit planes from the least sig-

nificant bit to

k − 1 most significant bits and

then encoded for image compression.

bit rate

(1) a measure of signaling speed;

the number of bits transmitted per second.
Bit rate and baud are related but not identi-
cal. Bit rate is equal to baud times the number
of bits used to represent a line state. For ex-
ample, if there are sixteen line states, each
line state encodes four bits, and the bit rate is
thus four times the baud. See also

baud

(2) the number of bits that can be trans-

mitted per unit time.

bit serial

processing of one bit per clock

cycle. If word length is

W, then one sample

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or word is processed in

W clock cycles. In

contrast, all

W bits of a word are processed in

the same clock cycle in a bit-parallel system.

For example: a bit serial adder with 4-

bit data has one input signal for each of data
them, one bit for carry-in, and two 4-bit shift
registers for data.

bit-line capacitance

the equivalent ca-

pacitance experienced in each “bit line” in a
RAM or ROM device. See also

bit line

bit-oriented block transfer (bitBLT)

type of processing used mainly for video in-
formation characterized by minimal opera-
tions performed on large data blocks; a pro-
cessor designed for such operations.

bit-

BLT operations include transfers, masking,
exclusive-OR, and similar logical functions.

bit-serial system

a system that uses bit

serial data transfer.

bit-slice processor

a processor organiza-

tion that performs separate computations (via
multiple processing units) separately upon
subsections of an incoming channel.

bitBLT

See

bit-oriented block transfer

bitmapped image

a digital image com-

posed of pixels.

Bitmapped images are

resolution-dependent, i.e., if the image is
stretched, the resolution changes.

Also

called a raster image. See also

image

pixel

vector image

bits per pixel

the number of bits used to

represent each pixel in a digital image. Typ-
ical grayscale images have 8 bits per pixel,
giving 256 different gray levels. True color
images have 24 bits per pixel, or 8 bits for
each of the red, green, and blue pixels. Com-
pressed image sizes are often represented in
bits per pixel, i.e., the total number of bits
used to represent the compressed image di-
vided by the total number of pixels.

BJT

See

bipolar junction transistor

black burst

a TV black video signal

containing horizontal and vertical sync, color
burst, and setup (i.e., a composite video black
signal).

Black burst is also called “color

black.” A black burst signal is often used
in the video studio to provide synchronizing
pulses.

black level

the portion of the video sig-

nal pertaining to the lower luminance (bright-
ness) levels.

black start

the task of re-starting an iso-

lated power system which is completely de-
energized. Most generating plants require
substantial external electric power to start.
Thus a black start may be initiated by hand-
starting gas turbine generators or by opening
the gates of a hydroelectric generator some-
where in the system.

blackbody

theoretically contrived object

that gives rise to the so-called “black body ra-
diation.” One might imagine a closed surface
object (say of metal) possessing one open-
ing that connects the interior surface with the
outside world. When the object is heated, the
opening becomes a perfect “black” radiator.
Such radiation depends on temperature only.

blackout

total loss of power to the entire

power system.

blanket

an insulating rubber mat which is

fitted temporarily over energized conductors
to protect nearby workers.

blanking

the electronic control circuitry

that blanks the television raster during hori-
zontal and vertical retrace.

blanking time

the short time interval

when both switches in a leg of an inverter
bridge must be off in order to prevent short
circuiting the DC input. This is necessary be-
cause non-ideal switches cannot turn on and
off instantaneously. Thus, after one switch is
turned off in an inverter leg, the complimen-

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tary switch is not turned on until the desig-
nated blanking time has elapsed.

blind deconvolution

the recovery of a sig-

nal

x[n] from y[n] — the convolution of the

signal with an unknown system

h[n]:

y[n] = h[n] ∗ x[n].

Occasionally, some knowledge of

h[n] is

available (e.g., that it is a high-pass or low-
pass filter). Frequently, detailed knowledge
is available about the structure of

x. See also

convolution

blind via

a via connected to either the

preliminary side or secondary side and one
or more internal layers of a multilayer pack-
aging and interconnecting structure.

blink

in computer display systems, a tech-

nique in which a pixel is alternatively turned
on and off.

Bloch vector

a set of linear combinations

of density matrix elements, written in vector
form, that can often be related to specific ob-
servables in a quantum mechanical system.
For example, in two-level systems the Bloch
vector components are 2

Re(ρ

), 2Im(ρ

and

− ρ

, which are related to nonlin-

ear refractive index, absorption, and popula-
tion differences, respectively. The time evo-
lution of two-level systems can be described
in terms of rotations of the Bloch vector.

block

a group of sequential locations held

as one unit in a cache and selected as whole.
Also called a line. See also

memory block

block cipher

an encryption system in

which a successive number of fundamen-
tal plaintext information symbols, usually
termed a block of plaintext information, are
encrypted according to the encryption key.
All information blocks are encrypted in the
same manner according to the transforma-
tion determined by the encryption key. This
implies that two identical blocks of plaintext

information will always result in the same ci-
phertext when a particular block cipher is em-
ployed for encryption. See also

encryption

stream cipher

block code

a mapping of

k input binary

symbols into

n output symbols.

block coding

(1) an error control coding

technique in which a number of information
symbols, and blocks, are protected against
transmission errors by adding additional re-
dundant symbols. The additional symbols
are usually calculated according to a mathe-
matical transformation based on the so-called
generator polynomial of the code. A block
code is typically characterized by the param-
eters

(n, k), where k is the number of infor-

mation symbols per data word, and

n the fi-

nal number of symbols in the code word after
the addition of parity symbols or redundant
symbols. The rate of a block code is given
by

k/n.

Typically, the lower the rate of a code

the greater the number of errors detectable
and correctable by the code. Block codes
in which the block of information symbols
and parity symbols are readily discernable,
are known as systematic block codes. The
receiver uses the parity symbols to deter-
mine whether any of the symbols were re-
ceived in error and either attempts to cor-
rect errors or requests a retransmission of
the information. See also

(2) refers to (channel) coding schemes

in which the input stream of information
symbols is split into nonoverlapping blocks
which then are mapped into blocks of en-
coded symbols (codewords). The mapping
only depends on the current message block.
Compare with

trellis coding

block diagram

a diagrammatic represen-

tation of system components and their inter-
connections. In elementary linear systems,
the blocks are often defined by transfer func-
tions or state space equations while the inter-

2000 by CRC Press LLC

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