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Glitch on ADC using FPGA module and different clocks

Hello !

 

I'm using PXIe and FPGA modules (5781 I/O modules + PXIE-7962R FlexRIO  and PXIE-1075 chassis) and I'm experiencing some problems related to the ADC...

 

I've reduced the problem to its simplest form (see attached screenshot) and when recording a DC signal and transferring it to server using FIFO, it appears that some digital glitchs occur (up to 1 every 10 microsecond)... see atached picture for an example...

 

The problem occurs when using all available FPGA clocks OTHER than IOModuleClock0/IOModuleClock 0 and 1.

 

However, for my "real" application, I need to decimate the clock (at 20 Mhz and below) and to use triggers, such that none of those clocks can be used (IOModuleClock0/IOModuleClock 0 does not support PXI triggers and IOModuleClock0/IOModuleClock 1 doesn't support clock decimation)...

 

So 3 solutions could be proposed :

-1. using onboard 40 MHz clock and avoid ADC glitches 

-2. using IOModuleClock0/IOModuleClock 0 and enabling PXI triggers

-3. using IOModuleClock0/IOModuleClock 1 and enabling clock downsampling (decimation)

 

Unfortunately, none of those solutions are possible for now... Could you please help me ?

 

Here is my software configuration:

- Labview 2010 SP1

- FlexRIO 1.6.0

- Compact RIO 3.6

- FlexRIO Adapter Module Support 2.2.0 (has been updated as suggested here :http://forums.ni.com/t5/LabVIEW/fpga-IO-module-clock-with-TRIG/td-p/1750046)

 

Thanks in advance !

Best regards

 

Nicolas

 

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Hi Nicolas, 

 

I noticed that you asked this question some time ago so I wanted to see if you were able to resolve the issue.  Do you still need assistance?

 

Regards, 

 

Brandon Treece 

Applications Engineer 

National Instruments

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Thanks for your answer...

We had some support from NI and it appears that the only way to ensure synchronisation betwen channels is to use IOModuleClock0/IOModuleClock 0... With the latest drivers, PXI Triggers are enabled... so this worked well for us !

THanks for the suport

Regards

Nicolas

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