Chapter 5
Analog Output
5-2
ni.com
•
AO Sample Clock
—The AO Sample Clock signal reads a sample
from the DAC FIFO and generates the AO voltage. Refer to the
section for more information.
•
Isolation Barrier and Digital Isolators
—Refer to Chapter 9,
Isolation and Digital Isolators on USB-6215/6216/6218 Devices
for more information.
AO Range
The AO range is ±10 V for USB-621
x
devices.
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
—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
—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 acq
u
isitions:
–
The time between samples can be m
u
ch shorter.
–
The timing between samples can be deterministic.
