18WuD2x

pull-in voltage • pulse droop 561
pull-in voltage The voltage required to close a relay.
pull switch A mechanical switch actuated by a
pulling action.
pullup Descriptive of a circuit or component used
to raise the value (e.g., impedance) of a circuit to
which it is connected.
pulsar An extremely dense, rapidly rotating collapsed
star that produces radio signals at regular
intervals. The pulse frequency varies from less
than one hertz to several tens or hundreds of
hertz.
pulsating direct current A direct current that periodically
rises and falls between zero and a maximum
value (or between two positive or negative
values) without changing polarity. Thus, it is possible
to have either a pulsating positive current or
a pulsating negative current. Also see DIRECT
CURRENT.
Voltage
+10
+8
+6
+4
+2
0
pulsating direct current
Time
pulsating wave See PULSATING DIRECT CUR-
RENT.
pulse A transient signal that is usually of short duration,
constant amplitude, and one polarity. A
typical example is a narrow positive or negative
spike.
pulse amplifier An amplifier having wide frequency
response and low distortion, used for amplifying
steep-sided pulses of short duration.
pulse-amplitude modulation Abbreviation, PAM.
A method of conveying information in wireless
communications. A train of pulses is transmitted.
The strength of each individual pulse varies according
to the modulating waveform. Normally,
the pulse amplitude increases as the instantaneous
modulating-signal level increases (positive
modulation). However, this can be reversed so
that higher audio levels cause the pulse amplitude
to go down (negative modulation).
pulse bandwidth For an amplitude pulse, the minimum
bandwidth occupied. The faster the rise
and/or decay times of a pulse, the greater the
bandwidth. The greater the pulse frequency, the
greater the bandwidth.
pulse code A code in which groups of pulses represent
digits.
pulse-code modulation Abbreviation, PCM. A
method of conveying information in wireless communications.
A train of pulses is transmitted. The
intelligence-carrying signal is sampled periodically
and the amplitude is converted into binary
code. The code might allow for eight levels
(000 to 111), 16 levels (0000 to 1111), 32 levels
(00000 to 11111), or 64 levels (000000 to 111111).
pulse-code-modulation binary code A pulse code
used in communications not in the form of line
transmission. Individual values are denoted by
binary numbers.
pulse-code modulation multiplex equipment A
multiplexer/demultiplexer for signal conversion
between a single signal and multiple-channel signals.
It uses both pulse-code modulation and
time-division multiplexing.
pulse-count divider A circuit or device that receives
an input of a certain number of pulses (or pulses
per second) and delivers an output that is a function
of that quantity. See, for example, DIVIDE-BY-
SEVEN CIRCUIT and DIVIDE-BY-TWO CIRCUIT.
pulse counter A circuit or device that indicates the
number of pulses presented to it in a given time
interval.
pulse counting Counting pulses in a sequence. At
low speed (pulse repetition rate), this can be done
with an electromechanical dial-type counter. At
high speed, a fully electronic circuit is required.
pulse delay circuit A monostable multivibrator
adapted to deliver its single output pulse a predetermined
time after the input pulse has been applied.
pulse dialing A form of telephone dialing in which
each digit is formed by a series of pulses, usually
at 10 to 20 Hz. The pulses are the equivalent of
disconnecting the line for a few milliseconds. Each
digit has the corresponding number of pulses, except
digit 0, which is formed by 10 pulses.
pulse droop Distortion observable as a downwardsloping
top on the oscilloscope trace of a pulse. It
can be quantified in volts, millivolts, microvolts,
amperes, milliamperes, or microamperes.
Voltage
+8
+6
+4
+2
0
pulse droop
Droop
Time