Alias-Free Bandwidth - National Instruments NI USB-9234 User Manual

Understanding NI USB-9234 Data Rates
© National Instruments Corporation
Stopband
The filter significantly attenuates all signals above the stopband frequency.
The primary goal of the filter is to prevent aliasing. Therefore, the stopband
frequency scales precisely with the data rate. The stopband rejection is the
minimum amount of attenuation applied by the filter to all signals with
frequencies within the stopband.

Alias-Free Bandwidth

Any signal that appears in the alias-free bandwidth of the NI USB-9234 is
not an aliased artifact of signals at a higher frequency. The alias-free
bandwidth is defined by the ability of the filter to reject frequencies above
the stopband frequency, and it is equal to the data rate minus the stopband
frequency.
The frequency of a master timebase (f
NI USB-9234. The NI USB-9234 includes an internal master timebase
with a frequency of 13.1072 MHz, but the module also can accept an
external master timebase or export its own master timebase. Refer to the
software help for information about configuring the master timebase source
for the NI USB-9234.
The following equation provides the available data rates of the
NI USB-9234:
where n is any integer from 1 to 31.
The data rate must remain within the data range. Refer to the
section for more information about the data rate range. When using the
internal master timebase of 13.1072 MHz, the result is data rates of
51.2 kS/s, 25.6 kS/s, 17.067 kS/s, and so on down to 1.652 kS/s, depending
on the value of n. When using an external timebase with a frequency other
than 13.1072 MHz, the NI USB-9234 has a different set of data rates.
) controls the data rate (f
M
( ) ÷
f 256
M
------------------------ -
f =
s
n
15 NI USB-9234 User Guide and Specifications
) of the
s
Specifications