Daisy Chain
A method of
propagating signals along a bus in which the devices are connected in series
and the signal passed from one device to the next. The daisy chain scheme
permits assignment of device priorities based on the electrical position of the
device on the bus.
Dallastat
Trademark for Dallas
Semiconductor's line of digital rheostats (digital potentiometers). (Dallas
Semiconductor is a subsidiary of Maxim Integrated.)
Data Acquistion System
System which
acquires data, generally by digitizing analog channels and storing the data in
digital form. These systems can be standalone or married to a computer and can
acquire multiple channels of data.
dB
Decibels: A method for specifying the
ratio of two signals.
dB = 10 times the log of the ratio of the power of the two
signals. This is equal to 20 times the ratio of their voltages, if the signals
are driving equal impedances.
Decibels are also used to describe a signal level by
comparing it to a reference level. The reference is usually defined as 0dB and
the dB value of the signal is 10 times the log of the signal's power over that
of the reference. A letter is sometimes added to signify the reference. For
instance, dBm is relative to 0 dBm = 1mW.
DBS
Direct Broadcast Satellite: A system which broadcasts
directly from satellite to the subscriber (end user). Prominent examples in the
US are DirecTV and Dish network.
DDR Memory
Double Data Rate Synchronous DRAM: A clock is used to read
data from a DRAM. DDR memory reads data on both the rising and falling edge of
the clock, achieving a faster data rate. Often used in notebook computers
because it also consumes less power.
DDS
DDS (direct digital synthesis) is a
method for digitally generating analog waveforms, such as sine waves (modulated
or not) or arbitrary waveforms.
In the most straightforward realization, a digitized sample
of the waveform is stored and the values are clocked out to a D/A converter.
Varying the clock rate changes the frequency. Variations in rate and changes to
a gain factor can modulate the signal.
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