18WuD2x

urst generator • button microphone 91
mance of such devices as amplifiers, filters, electronic
switches, transducers, and loudspeakers.
burst transmission A short transmission at high
speed. This method of transmission saves time,
but increases the necessary bandwidth of a signal
by the same factor as the ratio of the high
speed to the original speed.
bus 1. A main conductor in a circuit. A bus can be
high in the sense that its potential is above or
below ground, or it can be low or at ground reference.
2. In computer operations, a common
group of paths over which input and output signals
are routed.
bus driver A buffering device designed to increase
the driving capability of a microprocessor, which
itself might be capable of driving no more than a
single load.
business machine Any piece of electronic or electromechanical
equipment used mainly, or entirely,
for business purposes. Examples are photocopiers,
facsimile (fax) machines, printers, and computers.
busing The parallel interconnection of circuits.
busy test A check conducted to find out whether or
not a certain telephone subscriber line is in use.
busy tone Also called busy signal. An intermittent
tone that indicates that the subscriber line being
called is in use.
Butler oscillator An oscillator that consists of a
two-stage amplifier with a quartz crystal in the
positive-feedback path from output to input.
butterfly capacitor A plate-type variable capacitor
that has two stator sections and a single rotor
section common to the two stators. External connections
are made to the stators only. Thus, no
wiping contact is required to the rotor, and the
troubles associated with such a contact are
avoided. The butterfly capacitor is actually two
variable capacitors in series. The unit is so called
from the shape of its rotor.
circuit. The ring supplies the inductance, and the
butterfly supplies the capacitance. It is also
called butterfly tank and butterfly resonator.
Butterworth filter A high-pass, low-pass, bandpass
or band-rejection filter, characterized by a
flat passband (absence of passband ripple) and
high attenuation at frequencies far removed from
the passband.
Butterworth function A mathematical function
that is used in the design of a BUTTERWORTH
FILTER.
button 1. Usually, a small switch that is actuated
by finger pressure. It is also called pushbutton
and pushbutton switch. Sometimes, the term is
applied only to the insulated knob or pin which is
pushed to operate the switch. 2. A tiny lump of
impurity material, placed on the surface of a
semiconductor wafer for alloying with the wafer
to form a junction. See ALLOY JUNCTION. 3. The
carbon element(s) in a BUTTON MICROPHONE.
button capacitor A button-shaped ceramic or silvered-mica
fixed capacitor. Because of its disk
shape and mode of terminal connection, it offers
very low internal inductance.
button microphone A microphone in which a button-shaped
carbon element is attached to a diaphragm,
which is set into vibration by sound
waves. This motion causes the button resistance
to vary, modulating a direct current that passes
Diaphragm
Carbon
granules
Single button
Sound
waves
Stator 1
Rotor
Output
Stator 2
Sound
waves
Double button
Carbon
buttons
Output
voltage
butterfly capacitor
Diaphragm
butterfly circuit A combination of a butterfly capacitor
and a ring, of which the stator plates of
the capacitor are an integral part. The resulting
structure is a compact variable-frequency tuned
button microphone