© National Instruments
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3-7
Figure 3-9.
SCB-68A Circuit Diagram for Analog Output Lowpass Filter
Analog Output Lowpass Filtering Applications
The following applications benefit from lowpass filtering:
•
Protection for external circuitry
—Lowpass filters can smooth stairstep-like curves on
AO signals. If the curves are not smoothed, the AO signals can be a hazard for some
external circuitry connected to it. Figure 3-10 shows the output of a lowpass filter when a
stairstep-like signal is the input.
Figure 3-10.
Lowpass Filtering of AO Signals
•
Deglitching analog output signals
—Lowpass filters can be used to decrease glitches from
an analog 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 of the DAC code changes. You can build a lowpass
deglitching filter to remove some of these glitches, depending on the frequency and nature
of the output signal. To select a cutoff frequency for the deglitching filter, refer to your
DAQ device documentation for the maximum glitch duration.
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S
C
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A
B
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AO 0
AO GND
Time (t)
V
o
lts (V)
