PXI-6552 HSDIO bandwidth

[Newbie217]

Hello,

I am new to using the NI PXI-6552 HSDIO systems. The spec sheet says that the device is rated up to 100 MHz in bandwidth. For my application, I will be needing to generate and acquire signals up to 33 MHz. To simply test out the HSDIO hardware, I ran the express config LabVIEW vi for the HSDIO instrument. I tried generating some squarewave signals, and noticed significant distortion in the 10 MHz range. I am wondering if my hardware needs to be setup a certain way to perform properly. Currently, I am using the intneral clock and connecting the channels directly from the HSDIO to a 2.5 Gs/s, 350 MHz Tektronix oscilloscope. The connection I am using is SMB-BNC.

I have included some scope shots to illustrate my problem. The distortions become very noticable in the low MHz. range. Thanks for any help I can get.

[Jordan F]

Hi The PXI-6552 has an on board clock frequency range of 48 Hz to 100MHz (configurable to 200MHz/N, where 2 <= N <= 4,194,304) so you should be able to generate and acquire up to the specified max frequency (33 MHz).  The distortion probably lies within your oscilloscopes bandwidth or impedance.  I attached two different pictures that illustrate the difference between some of our High Speed Digitizers (5154 and the 5124).  The difference between these scopes is the bandwidth (5154 - 1 GHz, 5124 – 150 MHz).  As you can see, there is some distortion of the square wave when using the 5124 at 10MHz.  This is caused by the high frequency component (order) of the sine waves that make up the square wave signal.  So, since the bandwidth is lower on the 5124, the square wave appears to be distorted.  This is why you were measuring a better square wave signal at a lower frequency.  Also, these measurements were done using a 50 ohm cable with 50 ohm impedance on the oscilloscope.  This would be something to check because if you are not matching the impedance you could see reflections on your measurement that would cause distortion. 

Here is a helpful article on our website that explains more about using oscilloscopes.

https://www.ni.com/en/shop/electronic-test-instrumentation/oscilloscopes/top-10-things-to-consider-w... 

Here is the support page for the PXI-6552.

[Jordan F]

Also, I would recommend to read the two articles below.  They go over proper termination for digital input/output devices and cabling considerations.

Proper Termination for High-Speed Digital I/O Applications 

Termination and Cabling Considerations for HSDIO 

Let me know if this helps!

[Newbie217]

Hi Jordan,

Thanks so much for your help, I really appreciate it! I've tried changing the scope's impedance, and tried a variety of different probes, but so far I'm still getting the same problem. I will take your advice and try a higher bandwidth scope, and look for the proper cable to use. Hopefully this solves the problem.