scxi 1120 low pass filter specs for anti aliasing

[Fat Controller]

Hia,

I'm am currently finnishing the development of a multi channel spectral analysis unit and I am concerned about aliasing. I have observed that the 1120 isolation amplifiers that I am using have a two position low pass filter for 4Hz and 10kHz now my problem is this, I'm sampling at 25600Hz and thus need to attenuate the signals by 12800, as i am using a 16bit AD card to be able to maximise its resolution I need to attenuate the signals to -92 dB  (or -96 dB  I can't remember which one) by this frequency.

does anyone have details of the 1120's 10kHz filter? can I get away with using this or do I need to use a speciallist anti aliasing filter (which wouldn't be as tough a filter as I am only interested in signals up to 5kHz so I could have a much slower roll off)\

Cheers

Any help would be appreciated

[Logan_K]

The specific characteristics of the SCXI-1120 are not available because the filter is not high-performance since it is designed speicifically for noise rejection. From the SCXI-1120 user's manual (http://www.ni.com/pdf/manuals/320425d.pdf), you can see that there are two lowpass filter stages, and then there is also a bandwidth limitation imposed by the amplifiers. The two filter stages are simple RC filters, so I would doubt that the roll-off is steep enough to reach -92dB attenuation at 12.8kHz. I would recommend either designing your own first stage filter, like you had mentioned, or find a way to increase your sample rate.

-Logan

[Fat Controller]

that is what I thought but hoped wasn't the case, looks like a few more dollars will need to be spent.

Cheers

The Fat