18WuD2x

phase compensation • phase opposition 525
phase compensation In an operational amplifier,
compensation for excessive phase shift in the
feedback.
phase compressor A push-pull phase-inverter circuit
in which a capacitor is connected between
each collector or drain and the opposite output
terminal to attenuate in-phase components, such
as even-numbered harmonics.
phase constant A figure providing the rate (in degrees
of phase per unit length) at which the phase
lag of the current or voltage field component in a
traveling wave increases linearly in the propagation
direction.
phase corrector A circuit that returns a signal to a
certain phase after the signal has passed through
a circuit or medium that has caused phase distortion.
phased antenna See PHASED ARRAY.
phased array Also called phased antenna. An antenna
system having two or more driven elements
fed with a certain relative phase, and spaced at a
certain distance, resulting in a directivity pattern
that exhibits gain in some directions and little or
no radiation/response in other directions. Such
an array can have two elements, producing a unidirectional
cardioid or bidirectional figure-eight
pattern. More complex arrays have several elements,
usually vertical antennas, strategically
positioned and fed with signals of specified phase
to produce a highly tailored pattern. The most sophisticated
systems have rotatable or steerable
radiation/response patterns.
phase-delay equalizer See DELAY EQUALIZER.
phase detector See PHASE-SENSITIVE DETEC-
TOR.
phase diagram A graphical representation of
waves having equal frequency, but differing in
phase. The phase difference for two identical
waveforms is greater than or equal to zero degrees,
but less than 360 degrees.
phase difference 1. The difference (in time, angle,
or fractional cycle) between the instants at which
two alternating quantities reach a given value.
2. For a dielectric, the complement of PHASE AN-
GLE; that is, 90 degrees minus the phase angle in
degrees.
phase discriminator See DISCRIMINATOR, FOS-
TER-SEELEY DISCRIMINATOR, RATIO DETEC-
TOR, and TRAVIS DISCRIMINATOR.
phase distortion Distortion characterized by input/output
phase shift between various components
of a signal passed by a circuit or device.
phase inverter A resistance-capacitance-coupled
amplifier with a single-ended input and a pushpull
output. This circuit enables a push-pull amplifier
to be driven without an input transformer.
phase-locked loop Abbreviation, PLL. An oscillator
that combines the flexibility of a conventional
variable-frequency oscillator (VFO) with the stability
of a crystal oscillator. The oscillator output
is passed through a programmable divider that
Signal
input
(from IF)
Phase
comparator
Voltagecontrolled
oscillator
Filter Amplifier Output
Control
voltage
phase-locked loop
divides the frequency by a specific integral value
n chosen by the operator. The output frequency
of the divider is locked, by means of a phase comparator,
to the signal from a crystal-controlled
reference oscillator. As long as the output from
the divider is exactly at the reference-oscillator
frequency, the two signals are in phase, and the
output of the phase comparator is zero volts dc. If
the VCO frequency changes, the phase also
changes, and the phase comparator produces a
dc error voltage. The error voltage is applied to the
VCO, causing the VCO frequency to correct itself.
This maintains the VCO frequency at precisely n
times the reference-oscillator frequency.
phase-locked oscillator An oscillator in which the
inductance or the capacitance is varied periodically
at half the driving frequency.
phase margin In an integrated-circuit amplifier,
the extent to which the device shifts the phase of
a signal more or less than one-half cycle (180 degrees)
for a certain signal voltage.
phase modulation Abbreviation, PM. A method of
modulation in which the phase of the carrier current
is varied in accordance with the instantaneous
modulating-signal voltage. The result is
similar to FREQUENCY MODULATION.
phase modulator A circuit or stage that produces
PHASE MODULATION.
phase multiplier A circuit used for the purpose of
phase comparison between signals. The frequency
of the measured signal is multiplied, resulting
in multiplication of the phase difference.
This improves the sensitivity of the measuring
apparatus.
phase opposition For signals having the same frequency,
the condition of their being inverted relative
to each other in terms of instantaneous
amplitudes, so positive peaks of the first signal
correspond to negative peaks of the second signal,
and negative peaks of the first signal correspond
to positive peaks of the second signal. This
is not the same thing as being shifted by an odd