I have a puzzle about the NI DAQ5112.

[kevinn]

I wonder know that why the sampling rate of DAQ5112 is 100MS/s and at the same time the frequency band is 100MHz.Your reference of this board have told me this. However, according to the Sampling Theory, if the sampling rate is 100MS/s, then the frequency band is at least half of the sampling rate. How to explain this?

[Michael_S.]

Kevin,

The analog front end of the NI 5112 has a bandwidth of 100MHz, which is the 3db point. If you recall at the 3db point or 100MHz your input signal will be attenuated by about 30% or the input signal is .707 of its original amplitude. The large bandwidth will decrease the amount of attenuation when you are measuring signals up to 50MHz. You are correct in your comments about the Nyquist Sampling Theory. If you are sampling at 100 MS/s the frequency content of the input signal should be less than 50MHz.

The 100MHz bandwidth also becomes valuable when using Random Interleave Sampling (RIS), which is also called Equivalent Time Sampling (ETS). The 5112 can sample repetitive signals at up to 2.5 GHz so you can measure signals with up to 100 MHz fr
equency content when using RIS acquisition mode.

[Mike_T]

Kevin,

One other thing to note with the NI 5112 is that you can software select a 20MHz bandwidth filter per channel. This can be set using the niScope_ConfigureChanCharacteristics function in a text based language such as C or LabWindows/CVI; or the niScope Configure Chan Characteristics.vi in LabVIEW. Set the maximum input frequency to 20e+6. Any other value will default to 100e+6.

[ziyad]

Does NI have plans for making a digitizer for more than 100MS/s realtime(at 12bit or more). I have to measure a non-periodic DC coupled AC waveform at 200MHz and in micro to millivolts range. According to nyquist i have to sample at 400MS/s. but Ni doesn't seem to have that type of speed or resolution.