Page 75 - Electrical Engineering Dictionary

cross section, or balanced with respect to vir- of the response curve. Frequency changes
tual ground. Balanced wiring configurations (FM) will result in corresponding amplitude
are often used to prevent noise problems such changes that are then sent to an AM detector.
as ground loops. Contrast with unbalanced The balanced version is two slope detectors
line. connected in parallel and 180 degrees out of
phase.
balanced load a load on a multi-phase
power line in which each line conductor sees ball grid array (BGA) a modern high
the same impedance. I/O count packaging method. It reduces the
package size and its pin-to-pin trace gap in
balanced mixer a nonlinear 3-port device order to integrate more functions and relia-
(two inputs, one output) used to translate an bility in a single space. It can have as many as
input signal’s frequency component either up 324 pins. BGA sockets are high speed, high
or down the frequency spectrum by generat- reliability, surface-mountable, and can be in-
ing the sum and difference of two or more stalled without soldering. The related terms
frequencies present at its inputs. The three are PBGA—plastic ball grid array, CBGA—
ports are termed RF (radio frequency), LO ceramic ball grid array, TBGA—tape auto-
(local oscillator), and IF (intermediate fre- mated bonded ball grid array. The disadvan-
quency). A balanced mixer translates the tage of BGA packaging is that new tools and
frequency components found in the RF in- skills are required to mount or replace the
put signal to the IF output in such a manner chipset manually for repair purposes.
as to minimize the amount of LO noise arriv-
ing at the IF. This reduces the mixer’s over- ballast a starting and control mecha-
all noise figure and increases its sensitivity. nism for fluorescent and other types of gas-
Other advantages of these mixers include im- discharge lamps. Initially a ballast supplies
proved local oscillator isolation and linearity the necessary starting (or striking) voltage in
and higher power handling ability. order to ionize the gas to establish an arc be-
tweenthetwofilamentsinthelamp. Oncethe
balanced modulator a modulator in gas is ionized, the ballast controls the input
which the carrier and modulating signal are power and thus the light output to maximize
introduced so that the output contains the two the efficiency and life of the lamp.
sidebands without the carrier.
balun a network for the transformation
balanced operation in n-phase circuits
from an unbalanced transmission line, sys-
(n > 1), an operating condition in which the
tem or device to a balanced line, system or
voltages (currents) of the phases are equal-
device. Baluns are also used for impedance
amplitude sinusoids with phase-angles dis-
transformation. Derived from “balanced to
placed by a specific angle φ. The angle (φ)
unbalanced.”
is a function of the number of phases (n). For
In antenna systems, baluns are used to
n = 2,φ = 90 degrees, for n = 3,φ = 120
connect dipole-type antennas to coaxial ca-
degrees. In machine analysis the term “bal-
ble, to balance the current on dipole arma-
anced” is also used to describe a machine that
tures, and to prevent currents from exciting
has symmetrical phase windings.
the external surface of the coaxial shield.
balanced slope detector an arrangement See also balanced, unbalanced line.
of two detectors designed to convert an FM
signal to AM for detection. This is accom- band reference name for a range of fre-
plished by setting the IF center frequency quencies. Current defined bands include the
so that it falls on the most linear portion following.

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2000 by CRC Press LLC