© National Instruments Corp.
15
NI 9229/9239
Stopband
The filter significantly atten
u
ates all signals above the stopband
freq
u
ency. The primary goal of the filter is to prevent aliasing.
Therefore, the stopband freq
u
ency scales precisely with the data
rate. The stopband rejection is the minim
u
m amo
u
nt of atten
u
ation
applied by the filter to all signals with freq
u
encies within the
stopband.
Alias-Free Bandwidth
Any signal that appears in the alias-free bandwidth of the
NI 9229/9239 is not an aliased artifact of signals at a higher
freq
u
ency. The alias-free bandwidth is defined by the ability of the
filter to reject freq
u
encies above the stopband freq
u
ency and eq
u
als
the data rate min
u
s the stopband freq
u
ency.
Understanding NI 9229/9239 Data Rates
The freq
u
ency of a master timebase (
f
M
) controls the data rate (
f
s
)
of the NI 9229/9239. The NI 9229/9239 incl
u
des an internal master
timebase with a freq
u
ency of 12.8 MHz, b
u
t the mod
u
le also can
accept an external master timebase or export its own master
timebase. To synchronize the data rate of an NI 9229/9239 with
other mod
u
les that
u
se master timebases to control sampling, all of