National Instruments 5411 - Manual (Page 60)

© National Instruments Corporation B-1 DAQArb 5411 User Manual
Appendix
B
Waveform Sampling and
Interpolation
This appendix describes the basics of waveform sampling and
interpolation.
According to Shannon’s sampling theorem, a digital waveform must be
updated at least twice as fast as the bandwidth of the signal to be
accurately generated. Even though the theoretical requirement for
update clock, f
c
, is twice that of the bandwidth of the signal of interest,
it is very difficult to design an analog filter that will reject the images
above the passband and also get maximum output bandwidth, as
represented by the curve, Analog Filter 1, shown in Figure B-1.
Analog Filter 2 represents a more practical filter. This filter is not as
aggressive and does not filter out the images near f
c
, but it does reject
all the others.
Figure B-1. Analog Filter and Signal Images without Digital Filtering
f
c
0
2f
c
3f
c
0.5f
c
Images
f
0
Analog Filter 2
Signal
Power
4f
c
Analog Filter 1