Page 35 - Electrical Engineering Dictionary

of a neuron to a smaller set of values. This active load a transistor connected so as to
set is usually [0, 1]. Typical functions are the replace a function that would conventionally
sigmoid function or singularity functions like be performed by a passive component such
the step or ramp. as a resistor, capacitor, or inductor.

active contour a deformable template active load-pull measurement a mea-
matching method that, by minimizing the surement method where transfer characteris-
energy function associated with a specific tics of a device can be measured by electri-
model (i.e., a specific characterization of the cally changing the load impedance seen from
shape of an object), deforms the model in the device. In an active load-pull measure-
conformation to salient image features. ment, the load impedance is defined by using
an output signal from the device and an in-
jected signal from the output of the device.
active device a device that can convert
energy from a DC bias source to a signal at
active logic a digital logic that operates
an RF frequency. Active devices are required
all of the time in the active, dissipative region
in oscillators and amplifiers.
of the electronic amplifiers from which it is
constructed. The output of such a gate is
active filter (1) a filter that has an en-
determined primarily by the gate and not by
ergy gain greater than one, that is, a filter that
the load.
outputs more energy than it absorbs.
(2) a form of power electronic converter active magnetic bearing a magnetic
designed to effectively cancel harmonic cur- bearing that requires input energy for stable
rents by injecting currents that are equal and support during operation. Generally imple-
◦
opposite to, or 180 out of phase with, the tar- mented with one or more electromagnets and
get harmonics. Active filters allow the out- controllers.
put current to be controlled and provide sta-
ble operation against AC source impedance activemixer amixerthatusesthreetermi-
variationswithoutinterferingwiththesystem nal devices such as FET rather than diodes as
impedance. nonlinear element. One advantage of active
The main type of active filter is the series mixers is that they can provide conversion
type in which a voltage is added in series with gain.
an existing bus voltage. The other type is the
parallel type in which a current is injected active network an electrical network
into the bus and cancels the line current har- that contains some solid state devices such as
bipolar junction transistors (BJTs) or metal-
monics.
oxide-silicon field effect transistors (FETs)
operating in their active region of the volt-
active impedance the impedance at the
age vs. current characteristic. To ensure that
input of a single antenna element of an ar-
these devices are operating in the active re-
ray with all the other elements of the array
gion, they must be supplied with proper DC
excited.
biasing.
active layer See active region. active neuron a neuron with a non-zero
output. Most neurons have an activation
active learning a form of machine learn- threshold. The output of such a neuron has
ing where the learning system is able to in- zero output until this threshold is reached.
teract with its environment so as to affect the
generation of training data. active power See real power.

c
2000 by CRC Press LLC