USB-6211 output anomilies

[nkeddem]

I am attempting to use a USB-6211 daq to perform low voltage (<100mV pk-pk) outputs.  I am using just the normal Output regeneration vi to create the output but it has very large zero crossing spikes.  Now I was reading about glitching, is this what I am experiencing?  And would an external sample and hold circuit alevate this problem?  I did read the maxim site dealing with deglitching but I am still a bit hazy as how to actually implement it in hardware.  If anyone has a more specific sample and hold implementation website using actualy hardware I would appreciate them posting it.  Would i need to route my sample clock to one of the digital pins and use that as my digital control for the sample and hold?

I have already attempted to put a low pass filter on the output and this helps the problem alot, but it doesn't aleveate it to a satisfactory output.

[JoeFriedchicken]

Hi,

You are correct: you are experiencing DAC output glitching [1]. Your scope shots look like the spike is about 50 mV, and the specifications say that the maximum glitching energy is about 100 mV over 2.6 us [2], so you're within expected behavior. If filtering isn't enough, than you should explore building a sample and hold circuit like you mentioned. I don't have any experience building such a circuit, but perhaps another community member does. I do know that you will need to use the same sample clock for the external circuit, and you can export the ao/SampleClock to PFI lines 4 through 7 to gain access to it.

[1] Reducing Glitches on the Analog Output of MIO DAQ Devices
http://digital.ni.com/public.nsf/allkb/9B13E25B0B0EC197862562B4007D2E33?OpenDocument

[2] NI USB-621x Specifications
http://www.ni.com/pdf/manuals/371932e.pdf