Page 216 - Electrical Engineering Dictionary

digital relay a relay in which decisions digital tachometer a device with a sensor
are made by a digital computer, typically a that senses pulses from a rotating axis and
microprocessor system. converts them to digital output calibrated in
rotations per minute (rpm).
digital serial processing processing of
more than one but not all bits in one clock digital voltmeter (DVM) a modern solid-
cycle. If the digit size is W 1 and the word statedevicecapableofmeasuringvoltageand
length is W, then the word is processed in displaying the value in digitized form. The
W/W 1 clock cycles. If W 1 = 1, then the term is also used loosely for the digital mul-
system is referred to as a bit-serial, and if timeter, which can also measure current and
W 1 = W, then the system is referred to as a resistance.
bit-parallel system. In general, the digit size
W 1 need not be a divisor of the word length digital–optical computing that branch of
W, since the least and most significant bits optical computing that involves the develop-
of consecutive words can be overlapped and ment of optical techniques to perform digital
processed in the same clock cycle. computations.

digital signal processor (DSP) micro- digital-to-analog converter (DAC, D/A)
processor specifically designed for process- a device that changes a digital signal to an
ing digital signals. DSPs are typically well analog signal of corresponding magnitude.
suited to perform multiplications and addi-
tions in chain, even in floating point. They digital-video effects application of digi-
are less suitable for managing interrupts and tal technology to manipulate video informa-
large amounts of memory. For reaching high tion for production, to compress video data,
performance, a neat division between mem- to transmit video signals, and to process or
ory for data and memory for programs is transform video signals for various display
adopted, with the constraint of having a high systems.
number of pins. The original analog video is digitized for
application to computer-type circuits that can
digital simulator a simulator that allows produce effects such as video mixing or over-
the user to check the function and perform a lay; editing of video signals; compression
timing analysis of a digital system. of video data; synchronizing video systems;
signal transformation and timebase correc-
digital subscriber line (DSL) in tele- tion for various display formats and signal
phony, a digital connection between a cus- conversion back to analog form. The primary
tomer premise and a central switching office video artifacts observed from the digital-
(CO) using twisted-pair (copper) as the trans- video effects result from either digitizing to
mission medium. Although DSLs were orig- an insufficient number of bits per picture el-
inally introduced for narrowband ISDN ap- ement (pixel) or from too few samples for
plications (144 kbps), recent enhancements the video block processing algorithms. Us-
of DSLs (definitions follow) now support a ing fewer than 8 bits/pixel for each color
broader range of higher-rate services. component will cause poor signal-to-noise
ratios and produce scenes that have the ap-
digital sum variation a measure of the pearance of a poster or cartoon. The poster
maximum possible imbalance in a line coded appearance results from contours that are too
sequence. Definitions vary; a common defi- abrupt and from colors that are not smoothly
nition is the total number of running digital blended. Similarly, algorithms that process
sum values that can arise in the encoded se- large blocks of pixels tend to reduce resolu-
quence. tion and produce blocks with color shifts.

c
2000 by CRC Press LLC