18WuD2x

114 chopper stabilization • chrominance modulator
chopper stabilization 1. Stabilization of directcurrent
(dc) amplification by using a CHOPPER
CONVERTER ahead of a stable ac amplifier, and
rectifying the amplifier output. 2. In a regulated
power supply, use of a CHOPPER AMPLIFIER at
the control-circuit input to improve regulation.
chopper-stabilized amplifier See CHOPPER AMP-
LIFIER and CHOPPER STABILIZATION, 1.
chopper transistor A transistor that provides
rapid and repeated on/off switching of direct current
(dc), in the manner of an electromechanical
interrupter. See CHOPPER.
chopping frequency The frequency at which a
chopper interrupts a signal.
chord 1. A harmonious mixture of musical tones of
various frequencies. 2. A straight line that joins
two points on a curve (such as an arc of a circle).
3. The width of an airfoil.
chord organ An electronic organ that will sound a
musical chord when a key is pressed (see
CHORD, 1).
choreographer program A computer program
similar to one originally written by Charles Lecht
of Lecht Sciences, Inc. The computer operator
gives commands that cause a human form, portrayed
on the display screen, to make various
movements. Used in animated computer graphics.
chorus Signals at very low radio frequencies
(VLF), natural in origin, that sweep upward in
frequency. Believed to result from lightninggenerated
electromagnetic fields that circulate in
the magnetosphere (earth’s magnetic field). The
term is derived from the sound the signals make
in high-gain audio-frequency (AF) amplifiers connected
directly to VLF receiving antennas.
Christiansen antenna A radio-telescope antenna
for obtaining high resolution. Two straight arrays
are placed at an angle, intersecting approximately
at their centers. The resulting interference
pattern has extremely narrow lobes.
Christmas tree A tree-like pattern on the screen of
a television receiver, caused by loss of horizontal
synchronization.
chroma The quality of a color: hue and saturation.
chroma circuit In color television, one of several
circuits whose ultimate purpose is to produce a
color component on the screen.
chroma-clear raster In color television reception,
the clear raster resulting from a white video signal,
or from operation of the chroma circuits of
the receiver (as if they were receiving a white
transmission). Also called white raster.
chroma control In a color television receiver, a
rheostat or potentiometer that permits adjustment
of color saturation through variation of the
chrominance-signal amplitude before demodulation.
chromatic fidelity See COLOR FIDELITY.
chromaticity 1. The state of being chromatic (see
CHROMA). 2. A quantitative assessment of a
color in terms of dominant or complementary
wavelength and purity.
chromaticity coordinate For a color sample, the
ratio of any one of the three tristimulus values
(primary colors) to the sum of the three.
chromaticity diagram A rectangular-coordinate
graph in which one of the three CHROMATICITY
COORDINATES of a three-color system is plotted
against another coordinate.
chromaticity flicker Flicker caused entirely by
chromaticity fluctuation (see CHROMATICITY, 2).
chromel A nickel-chromium alloy with some iron
content, used in thermocouples.
chromel-alumel junction A thermocouple that
uses wires of the alloys chromel and alumel.
chromel-constantan thermocouple A thermocouple
consisting of a junction between wires or
strips of chromel and constantan. Typical output
is 6.3 mV at 100°C.
chrome plating The process of coating a metal
with chromium. Generally protects against corrosion.
chrome recording tape Also called chrome tape or
chromium tape. Tape that is manufactured from
the compound chromium dioxide. Noted for its
ability to faithfully record and reproduce music.
chrominance In color television, the difference between
a reproduced color and a standard reference
color of the same luminous intensity.
chrominance amplifier In a color television circuit,
the amplifier separating the chrominance
signal from the total video signal.
chrominance cancellation On a black-and-white
picture tube screen, cancellation of the fluctuations
in brightness caused by a chrominance signal.
chrominance-carrier reference In color television,
a continuous signal at the frequency of the
chrominance subcarrier; it is in fixed phase
with the color burst and provides modulation
or demodulation phase reference for carrierchrominance
signals.
chrominance channel In color television, a circuit
devoted exclusively to the color function, as opposed
to audio and general control channels.
chrominance component In the NTSC color television
systems, either of the components (I-signal
or Q-signal) of the complete chrominance signal.
chrominance demodulator In a color television
receiver, a demodulator that extracts videofrequency
chrominance components from the
chrominance signal, and a sine wave from the
chrominance subcarrier oscillator.
chrominance gain control A rheostat or potentiometer
in the red, green, and blue matrix channels
of a color television receiver, used to adjust
the primary-signal amplitudes.
chrominance modulator In a color television
transmitter, a device that generates the chrominance
signal from the I and Q components and
the chrominance subcarrier.