AD4020 eval board external supply

Hi Moran,

Thanks for your patience as we continue to try to solve this.

I think this is my last "analog" question - does the code output issue occur only when your signal generator is connected to the EVAL-AD4020FMCZ inputs (i.e. the J7/J11 SMA connecotrs)? Or does it happen even when J7/J11 are not connected to anything? In the EVAL-AD4020FMCZ default configuration, if J7/J11 are not connected to any external source, then the AD4020 inputs will just be driven to VREF/2, and it should return a mean code of close to 0.

The reason I ask is that it's possible that depending on the output stage of your signal generator, it's possible that the ADA4807-1 inputs are getting dragged down to ground or some other voltage when it's connected. I know you said you verified the AD4020 IN+/IN- inputs are at 2.5V already but I just want to double check that this isn't the problem before we start debugging on the digital side.

In the meantime, you could also probe the SDO output of the AD4020 to see if it really is outputting the codes you're seeing in the eval software, or if there's some issue with the FPGA board as you suggested. I recommend probing CNV, SCK, and SDO and seeing what the state of SDO is on each SCK falling edge to see if the results displayed in the eval software match reality.

Hi taylor,

When the signal generator is not connected to the eval board, I typically see the output code to be 0. But before this whole issue started showing up, I would see a noise worth 60-70 codes around 0. However, after this issue, I just see a straight line of code 0.

I tried even that. The SDO is definitely toggling the way it's supposed to. But since the clock is not triggering properly (i.e, instead of 20 pulses, it's kind of showing up as one big pulse) we are getting an ENOB of 2 (0 and -500000). Hence, the output is following the frequency but not able to capture the wave. This was my conclusion after probing the SPI pins. Does this make sense?

Hi Moran,

Thanks for the info. If you're seeing this issue even with a brand new EVAL-AD4020FMCZ board when the signal generator is connected, then you're probably correct about it being an issue with the SPI. More specifically, with the SDP-H1 board for some reason. It's possible it was damaged when switching from the on-board supplies to the external ones, though I can't say for certain.

Just out of curiosity, when you say "SDO is definitely toggling the way it's supposed to," do you mean that the output codes you see on SDO match the 0 and -500000 you see in the AD4020 software, or that they are roughly code 0 with some noise around them?

Thanks,

Tyler

Hi Moran,

I've moved your query over to the SDP Support thread to make sure you get support from the SDP team, since we've narrowed down the problem to your SDP-H1 board. Someone should be able to help you out.

Thanks,

Tyler

Thanks a lot :)

No they are toggling between 0 and -500000