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Appendix B
Waveform Sampling and Interpolation
Signal
Power
f
0
0
0.5f
c
Without Interpolation
Note:
DAQArb 5411 User Manual
To ease the requirements of the analog filter and to get more output
bandwidth, the DAQArb 5411 uses a half-band digital filter to
interpolate a sample between every two samples at twice the update
frequency, 2f
. Also, the DAC operates at twice the sample frequency.
c
This increase pushes the images from f
roll-off easily rejects any images from the output spectrum. This
behavior can be seen in the frequency domain representation from
Figure B-2 and in the time domain representation from Figure B-3.
f
c
Figure B-2. Digital Filter, Analog Filter, and Signal Images with Digital Filtering
With Interpolation
The digital filter will be operational only for sample rates of 40 MHz and
20 MHz. For other sample rates, the digital filter will not be of any use.
Images
2f
c
After Analog Filtering
Figure B-3. Waveform Updates
B-2
to 2f
and the analog filter
c
c
4f
c
© National Instruments Corporation
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