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ADS1261EVM: Ground Loop

Part Number: ADS1261EVM
Other Parts Discussed in Thread: ADS1261

I currently have a very simple two wire setup on the ADS1261 evaluation board. I have 60 Hz noise on my data and I'm guessing it's because of ground loop somewhere. AIN7 is set as an IDAC (50uA) that drives a 10k resistor (R1) across AIN5 and AIN4. I also have a 15k reference resistor (R2) across AIN0 and AIN1. R1 and R2 are in series. I've tried attaching the negative side of R2 to ground and AVSS and also tried powering the board from external power supply. The attached photo is 400 SPS and a PGA gain of 1.

  • Hi Paul Carney.

    Can you try running the ADC at 60 SPS to see if the noise goes away? The 60 SPS data rate uses a filter setting that should reject 60 Hz frequencies. If you get good results with these settings, we can assume the line cycle frequency is somehow entering the system

    If that is the case, can you describe your system setup? Are you using a laptop or a PC? Are you near any components / equipment that could generate 60 Hz noise (other than lights)?

    You also mentioned that you tried attaching R2 to ground and AVSS - does that imply that R2 was not connected to ground or AVSS at some point? If so, what was R2 connected to? Again, it might help if you could provide a picture or description of your setup 


  • The noise goes away at 60 SPS. I have a USB going from my laptop going to the board, and an external power supply providing 5V to the board. I've tried unplugging my laptop from the wall but the noise persists. There isn't anything near me that should produce this level of noise but I can try a different room if necessary. I mentioned AVSS and GND because I wasn't sure if the potential between those nodes could cause this problem.

  • Hi Paul Carney,

    Can you power the EVM with the onboard supply (that is itself powered from the USB) instead of using an external supply to see if the noise goes away? Also make sure your laptop is not plugged in. If you have S1 set to 5V as shown below, then AVSS = GND and there should be no issues.

    If the issue persists then you must be picking up 60 Hz from another source, possibly lighting.