NiScope 5122 how to switch off filters (noise filter, antialias filter)

[mschmidt]

NiScope 5122 how can i switch off the antialias filter and the noise filter with LabView?

Thanks

[DFGray]

You have two options:

1. Use niScope Configure Chan Characteristics.vi and set the max input frequency to 100MHz.


2. Use a property node of the device. Set Active Channel to the channel you want to disable the filters on, then set Vertical : Maximum Input Frequency to 100MHz.

NOTES:

1. The 100MHz number is specific to the 5122. Consult your hardware users manual for appropriate values for other devices. NI-SCOPE will coerce the value you input to the next legal value, so anything over the antialias filter bandwidth will work.


2. To see an example of this code, drop the NI-SCOPE Express block, configure with 100MHz bandwidth, close the configuration page, open
   the front panel (choose Convert), then open the block diagram. The channel parameters will be in a loop about halfway across the diagram.

[SocDesignCenter]

The way to set only Anti-aliasing filter without Noise filter is to set the max input frequency as anything from 20MHz to 35MHz. Is this correct ?

[DFGray]

Not quite. You need to set the max input frequency to anything greater than 20MHz and less than or equal to 35MHz.

20MHz < max input frequency <= 35MHz

[tfasel]

I understand how to turn on and off these filters. My question is, are these analog or digital filters?

[psisterhen]

The anti-alias and noise filters on the 5122 are analog filters.

[Rob Hingle]

I am having aliasing issues when sampling at lower rates (<20MHz) and as far as I can tell, the anti aliasing filter is not active no matter what maximum input frequency I set.  How far down does that filter track?  Does it track at discrete frequency ranges or continuously?  I have even tried setting the max input freq to 1Hz and driving the digitizer with a 100kHz signal, which gave me full throughput of the input signal.  A simple 2 pole butterworth 1MHz lowpass passive filter all but completely solves my problem, but that solution is side stepping my real issue.  Why doesn't my anti-aliasing filter seem to work?

[psisterhen]

On the 5122, both the "noise" and "anti-alias" filters are fixed analog filters.  The cutoff of the noise filter is about 20 MHz, and the cutoff of the anti-alias filter is 35 MHz.  So "anti-alias" is something of a misnomer if you expect it to change based on your sample rate.  I'm referring to it as an anti-alias filter if you're using the maximum sample rate of the 5122 (100 MS/s). 

So if you're sampling at rates below 20 MS/s, there will be aliasing if your signal has content at frequencies more than half of your sample rate, no matter which filter is enabled.  So the best idea is to oversample or add an external analog filter, as you've done.

[Rob Hingle]

Then I will need a very wide band tracking anti aliasing filter, with cutoff frequencies from 5kHz up to 5MHz.  Any recomondations?