Chapter 5
Analog Output
©
National Instruments
5-3
X Series User Manual
Minimizing Glitches on the Output Signal
When yo
u
u
se a DAC to generate a waveform, yo
u
may observe glitches
on the o
u
tp
u
t signal. These glitches are normal; when a DAC switches from
one voltage to another, it prod
u
ces glitches d
u
e to released charges. The
largest glitches occ
u
r when the most significant bit of the DAC code
changes. Yo
u
can b
u
ild a lowpass deglitching filter to remove some of
these glitches, depending on the freq
u
ency and nat
u
re of the o
u
tp
u
t signal.
Visit
ni.com/
s
upport
for more information abo
u
t minimizing glitches.
Analog Output Data Generation Methods
When performing an analog o
u
tp
u
t operation, yo
u
can perform
software-timed or hardware-timed generations.
Software-Timed Generations
With a software-timed generation, software controls the rate at which data
is generated. Software sends a separate command to the hardware to initiate
each DAC conversion. In NI-DAQmx, software-timed generations are
referred to as on-demand timing. Software-timed generations are also
referred to as immediate or static operations. They are typically
u
sed for
writing a single val
u
e o
u
t, s
u
ch as a constant DC voltage.
Hardware-Timed Generations
With a hardware-timed generation, a digital hardware signal controls the
rate of the generation. This signal can be generated internally on yo
u
r
device or provided externally.
Hardware-timed generations have several advantages over software-timed
generations:
•
The time between samples can be m
u
ch shorter.
•
The timing between samples can be deterministic.
•
Hardware-timed acq
u
isitions can
u
se hardware triggering.
Hardware-timed operations can be b
u
ffered or hardware-timed single point
(HWTSP). A b
u
ffer is a temporary storage in comp
u
ter memory for
to-be-transferred samples.
•
Hardware-timed single point (HWTSP)
—Typically, HWTSP
operations are
u
sed to write single samples at known time intervals.
While b
u
ffered operations are optimized for high thro
u
ghp
u
t, HWTSP
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