Chapter 3
Analog Output
©
National Instruments Corporation
3-3
Analog Output Series User Manual
Reference Selection (NI 6711/6713/DAQCard-6715 and NI 6731/6733
Only)
You can connect each DAC to the device internal reference of 10 V or to
the external reference signal connected to the external reference (AO EXT
REF) pin on the I/O connector. This signal applied to AO EXT REF should
be within ±11 V of AO GND. You do not need to configure all channels for
the same mode. Using AO EXT REF to reduce the output voltage range
results in a higher resolution at the adjusted range.
Reglitch Selection (NI 6711/6713 Only)
In normal operation, a DAC output glitches whenever it is updated with
a new value. The glitch energy differs from code to code and appears as
distortion in the frequency spectrum. Each AO channel contains a reglitch
circuit that generates uniform glitch energy at every code rather than large
glitches at the major code transitions. This uniform glitch energy appears
as a multiple of the update rate in the frequency spectrum. This reglitch
circuit does not eliminate the glitches; it only makes them more uniform in
size. By default, reglitching is disabled for all channels; however, you can
use NI-DAQ to independently enable reglitching for each channel.
Minimizing Glitches on the Output Signal
When you use a DAC to generate a waveform, you may observe glitches
on the output signal. These glitches are normal; when a DAC switches from
one voltage to another, it produces glitches due to released charges. The
largest glitches occur when the most significant bit (MSB) of the DAC code
switches. You can build a lowpass deglitching filter to remove some of
these glitches, depending on the frequency and nature of the output signal.
Visit
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AO Data Generation Methods
When performing an analog output operation, there are several different
data generation methods available. You can either perform software-timed
or hardware-timed generations. Hardware-timed generations can be
non-buffered or buffered.