PXIe-6571 signal distortion

[Sruk]

Hi,

I've been running some tests on the 6571 (Generator) and found out that there is a strange signal distortion on the side of the Generator.

It looks like a distortion from the reflection on the signal line, but this is strange since I'm running test vectors at only 1 MHz. Also, I'm aware that by the 6571 specification rising/falling timing is declared at 1.2 ns. The Generator is set to High-Z output mode.

Any clues on whats happening here?!

Pattern Editor oscilloscope with no cables

Pattern Editor oscilloscope with 0R55 cables connected

[santo_13 · Accepted solution]

The waveform shape is correlating to the typical reflection, you might be able to make it better by adjusting TDR and adding a 50-ohm resistor in series with the DUT pin.

BTW, you're operating well above 1MHz evident from your time scale in hundreds of ns instead of microseconds. Once you're above 10MHz, you need an excellent high-speed trace implementation with proper terminations or you will see reflections.

Edit: This article might be helpful - https://www.ni.com/en-us/support/documentation/supplemental/18/interconnect-considerations-for-mipi-...

[Sruk]

Thank you Santhosh!

This was exactly what I and some of my colleagues had in mind but since you're always a word-of-wisdom I've posted the question here. I'll check the link you've sent!

Do you think that a direct test PCB to 6571 connection would be a good idea? That would ditch the cables and interconnect the Generator and DUT over the HD connectors.

Bye!

[santo_13]

You can connect directly to PCB but the traces must be designed for 50-ohm characteristic impedance and the DUT pins have to be 50 ohms to ground.

Typical mixed-signal DUTs do not have a 50ohm input impedance, in that case, you have to work around it by adding a series resistor.