Absolute phase performance of 4472

[pcgibson@yahoo.com]

What is the Absolute phase accuracy of the 4472 card?  Not the cross channel phase match but absolute phase accuracy?  What type of Digital Anti-alias filters are used?  Also I am confused in the specifications.  Is there anti-alias protection available above the 25ksa outlined in the spec's.

[Abhinav T]

Hi,

I am not sure what you mean by absolute phase accuracy but if I understand you correctly, you are concerned about the delay the anti-aliasing filter causes?

This Knowledge Base article details the delay that is caused for each measurement on the 4472. If you go to the specifications for the 4472 page 4 shows the frequency response of the anti-alias filter.

The anti-alias protection does not work well below 25kSa/s. If indeed you are sampling below 25kSa/s you will have to turn on Low-frequency alias rejection.

Hope this helps!

Abhinav T.
National Instruments

[pcgibson@yahoo.com]

Hi Abhinav,

Thanks for the response, but the specifications outline the amplitude characteristics of the AA filter, but not the phase.  The tech article outlining the sample delay is helpful, but in the end what I am really trying to figure out is the Digital AA filter a linear phase response filter?  Is it a FIR or IIR based filter that you are using?

Thanks

[Abhinav T]

Hi,

The digital filter is an FIR filter. The phase linearity is <±5° (according to the specifications)

Abhinav