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pulse train • purity control 563
pulse train A series of successive pulses of usually
one kind.
pulse transformer A transformer designed to accommodate
the fast rise and fall times of pulses
and similar nonsinusoidal waveforms. Such
transformers often use special core materials and
are made using special winding techniques.
pulse transmitter 1. A device that transmits a series
of pulses. 2. A pulse-modulated transmitter.
3. See PULSE MODULATOR.
pulse waveform The general shape of a pulse as it
appears on an oscilloscope display. The various
forms range from positive or negative halfsinusoids,
through rectangles, to thin-line spikes.
pulse width The horizontal dimension of a pulse
(i.e., its duration).
pulse-width modulation Abbreviation, PWM. Also
called pulse-duration modulation (PDM). A
method of conveying information in wireless communications.
A train of pulses is transmitted.
The width (duration) of each individual pulse
varies according to the modulating waveform.
Normally, the pulse width increases as the instantaneous
modulating-signal level increases
(positive modulation). However, this can be reversed
so that higher audio levels cause the pulse
width to decrease (negative modulation).
Modulating
waveform
pulse-width modulation
Pulse
amplitude
pump 1. In a parametric amplifier, the oscillator
that supplies the signal that periodically varies
the reactance of the varactor. 2. The pumping
signal in 1. 3. To perform the operation (pumping)
described in 1. 4. To increase the energy level
of an atom or molecule (by exposing it to electromagnetic
radiation) to such an extent that oscillation
or amplification occurs. A ruby laser, for
example, produces its intense, coherent beam as
a result of pumping. 5. The radiation used to
pump an atom or molecule. 6. The device producing
the radiation required to pump an atom or
molecule.
pump frequency The frequency of a PUMP voltage.
pumping A method of laser actuation. A series of
pulses, at the resonant frequency of the lasing
material, is injected to cause laser output.
pump oscillator An oscillator for producing a
pump voltage.
pump voltage The voltage of a pumping signal.
Also see PARAMETRIC AMPLIFIER and PUMP,
1, 2.
punch 1. A tool for cutting holes in metal chassis,
panels, and boxes for electronic equipment. 2.
High signal strength.
punch-in editing In audio recording, a feature
that allows convenient insertion of new
material on a tape. The tape recorder can be
switched instantly from Play to Record, and
back again, whenever the operator wants to add
material.
punchthrough In a bipolar transistor, the potentially
damaging condition resulting when the reverse
bias of the collector is increased to a voltage
high enough to spread the depletion layer entirely
through the base. This tends to effectively connect
the emitter to the collector.
punchthrough region The conduction region associated
with higher-than-punchthrough voltage,
in which bipolar-transistor current is excessive.
Also see PUNCHTHROUGH.
punchthrough voltage The voltage that causes
PUNCHTHROUGH in a given bipolar transistor.
puncture voltage See BREAKDOWN VOLTAGE, 1.
Pupin coil One of several loading coils that can be
inserted at intervals in series with a telephone
line to cancel line-capacitance effects and, thus,
improve the clarity of speech.
pure tone An audio-frequency (AF) tone having essentially
no harmonic content; a sine-wave AF
tone.
pure wave A wave containing no distortion products.
purging The removal of an undesired gas or other
substance from a system by introducing a material
to displace it.
purifier A power-line operated alternating-current
electromagnet that can be manually rotated in
front of a color-television picture tube to demagnetize
the tube. Also called a DEGAUSSER.
purity 1. In color television, complete saturation
of a hue. 2. In a waveform, complete freedom
from distortion. 3. The extent to which spurious
signals are attenuated in the output of a radio or
television transmitter. Also called spectral
purity.
purity adjustment In a color-television picture
tube, adjustment of each purity control for pure
color.
purity coil A variable-current coil around the neck
of a color-television picture tube that is used to
adjust color purity.
purity control For a purity coil, the variable resistor
that controls the current for color correction.