Page 132 - Electrical Engineering Dictionary

this reason, electrons generally move much charging current that portion of an elec-
faster than holes when an electric field is ap- tric power line’s current which goes to charge
plied to the semiconductor. the capacitance of the line. The charging cur-
rent is not available for power transmission.
charge conservation physical law (de-
rived from Maxwell’s equations) indicating chattering fast switching. The term
that no change in the total charge within a comes from the noise generated by the sus-
certain volume can exist without the proper tained rapid opening and closing of a switch-
flow of charge (current) through that volume. ing element. See also discontinuous control.

charge density describes the distribution Chattuck coil a finely wound solenoid
of charge along a line, on a surface or in a about a flexible, nonmagnetic core that is
volume. May be discrete or continuous. usually used in conjunction with a fluxmeter
to measure magnetic potential between two
charge-coupled device (CCD) a solid- points; a magnetic analog of a voltmeter.
state device used to record images. A CCD is
a digital device which counts the photons that CHDL See computer hardware descrip-
strike it by making use of the photoelectric tion language.
effect. In a typical CCD array, a large number
of such devices is collected into a 2-D grid. Chebyshev alignment a common filter
Each device corresponds to a single pixel, alignment characterized by ripples of equal
and the number of electrons in the device is amplitude within the pass-band and a steep
linearly related to the brightness or intensity rolloff in the vicinity of cutoff frequency.
value at that point in the CCD.
Chebyshev filter one of a class of com-
charge-coupled device detector a monly used low pass, high pass, band pass
charge-coupled device (CCD) connected to and band stop filters with an equiripple
photodetectors, where the photocharge is put characteristic, designed to achieve relatively
into the CCD potential wells for transport and rapid rolloff rates (See also Butterworth
processing. filter) near cutoff frequencies, at the expense
of a loss of monotonicity in either the pass-
charge-coupled-device memory large- bands or the stopbands.
capacity shift registers making use of charge-
coupled devices (CCD), i.e., MOS devices checkerboarding See fragmentation.
in which data bits are stored dynamically as
charge between a gate and the substrate. This checkpoint time in the history of exe-
forms a multigate MOS transistors with the cution at which a consistent version of the
source and drain terminals “stretched” apart, system’s state is saved so that if a later event
and a number of gate terminals in between. causes potential difficulties, the system can
The first gate terminal (closest to the source) be restarted from the state that had been saved
inserts bits (charge) into the register, and at the checkpoint. Checkpoints are impor-
the following gates are controlled with over- tant for the reliability of a distributed sys-
lapping clocks allowing the charge to move tem, since timing problems or message loss
along the array. At the far (drain) end, the bit can create a need to “backup” to a previous
under the final gate terminal is detected as a state that has to be consistent in order for the
change in current. overall system to operate functionally.

charge-spring model See electron checkpointing method used in rollback
oscillator model. techniques in which some subset of the sys-

c
2000 by CRC Press LLC