• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 46 subscribers
  • Views 100 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1261EVM: Periodic signal decay measurement for some samples

Youngho Cho
Prodigy 100 points
Part Number: ADS1261EVM

Hi,

I bought the ads1261evm board and found something weird while testing it.

It appears that some ad-converted samples are periodically measured pretty below the expected value,
as Power Supply Power Measurement (AVDD-AVSS)/4, DVDD/4, even when measuring without connecting any pins to the input mux.

What makes this happen?

Or is this a characteristic of sigma-delta adcs?

The condition of testing and results are as follows.

1) Test Condition

- Output data rate : 14,400SPS

- Digital filter : sinc5 filter (default, when >7200SPS)

- Conversion start delay : 189us

- Reference : internal reference enabled, REFP: AVDD, REFN: AVSS

- PGA/Gain : PGA mode / 1V/V

- Input MUX : 1) (AVDD-AVSS)/4, 2) DVDD/4, 3) No connection

2) Test Result

- (AVDD-AVSS)/4

- DVDD / 4

- No connection

Thank you for your answer in advance.

 Best Regards,

Youngho.

  • 0
    TI__Mastermind 35121 points

    Hi Youngho,

    Below are the results I got from my ADS1261EVM performing the same tests as you with the same settings. I did not see any issue with the measurements.

    • Are there any other register settings you might have changed?
    • Did you make any jumper modifications on the EVM, or otherwise modify the EVM in any way?
    • Do you have a good, solid USB connection to the computer? Is the USB being routed through a hub or going directly into your PC?

    The error you are seeing appears to be cyclical, occurring roughly every 250 samples. At 14,400 SPS, one sample = 0.069ms, so 250 samples = 250*0.069 = 17.36ms. This equates to 1/17.36ms = 58 Hz, or very close to line cycle frequency (50 or 60 Hz, depending on where you live). Do you have any line-cycle noise that could be getting picked up by the ADC or USB cable? If you are using a laptop, try unplugging from a docking station or power supply and use the PC on battery power only to see if the issue goes away.

    (AVDD - AVSS)/4 = 5V / 4 = 1.25V

    DVDD/4 = 3.3V / 4 = 0.825V

    No connection