low-pass equivalent (LPE) model
a
method of representing bandpass signals and
systems by low-pass signals and systems.
This technique is extremely useful when de-
veloping discrete time models of bandpass
continuous-time systems.
It can substan-
tially reduce the sampling rate required to
prevent aliasing and does not result in any
loss of information. This, in turn, reduces the
execution time required for the simulation.
This modeling technique is closely related
to the quadrature representation of bandpass
signals.
low-pass signal
a signal whose Fourier
transform has frequency components that are
small for frequencies greater than some inter-
mediate frequency value. To define mathe-
matically, let
X(ω) be the Fourier transform
of the signal then
X(ω) = 0 for |ω| > B,
for some
B > 0. In the strict sense, if B is
the smallest value for which the above holds,
then
B is the bandwidth of the signal.
low-power TV (LPTV)
a television ser-
vice authorized by the FCC to serve specific
confined areas. An LPTV station may typ-
ically radiate between 100 and 1000 W of
power, covering a geographic radius of 10 to
15 miles.
low-pressure discharge
a discharge in
which the pressure is less than a torr or a
few torrs; low-pressure gases can be easily
excited, giving spectra characteristic of their
energy structure.
lower frequency band edge
the lower
cutoff frequency where the amplitude is equal
to the maximum attenuation loss across the
band.
lower side frequency
the difference fre-
quency that is generated during the het-
erodyning process or during the amplitude-
modulating process. For example, if a 500
kHz carrier signal is amplitude-modulated
with a 1 kHz frequency, the lower side fre-
quency is 499 kHz.
LPE model
See
low-pass equivalent
model
.
LPTV
See
low-power TV
.
LQ control
See
linear quadratic control
.
LRM calibration
See
line-reflect-match
calibration
.
LRRM calibration
See
line-reflect-
reflect-match calibration
.
LRU
See
least recently used algorithm
.
LRU bits
a set of bits that record the
relative recency of access among pairs of
elements that are managed using an LRU
replacement policy.
If
n objects are be-
ing managed, the number of bits required is
n(n − 1)/2. Upon each access, n bits are
forced into certain states; to check one of the
objects to determine whether it was the least
recently accessed,
n bits need to be exam-
ined.
LRU replacement
See
least recently used
algorithm
.
LRU stack
a stack-based data structure to
perform the bookkeeping for a least recently
used (LRU) management policy. An object
is promoted to the top of the stack when it is
referenced; the object that has fallen to the
bottom of the stack is the least recently used
object.
LS algorithm
See
least squares algorithm
.
LSB
See
least-significant bit
.
LSI
See
large-scale integration
.
LTC
See
load tap changer
and
tap
changing under load
.
LTI
See
linear time invariant system
.
c
2000 by CRC Press LLC