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ADS131E08: How to Suppress Industrial Frequency Noise in Sampling

Yivi Chan
Prodigy 75 points

Part Number: ADS131E08

Tool/software:

During the testing of the ADS131E08, we observed some noise issues. After shorting the ADC inputs and initiating conversion, FFT analysis of the acquired data revealed 50Hz and its odd harmonic components in the noise spectrum, which are affecting the ADC's sampling accuracy. How can we eliminate this power-line interference at the hardware level?

The application scenario is in the power industry where the target signal itself is 50Hz. Using digital filters would distort harmonic measurements.
FFT frequency point：

[  50.   149.5  150.   250.   349.5  350.   449.5  450.   549.5  550.  649.5  650.   749.5  750.5  849.5  850.   850.5  949.5  999.5 1049. 1049.5 1050.  1050.5 1148.5 1149.  1149.5 1150.  1150.5 1248.5 1249. 1249.5 1250.  1250.5 1251.  1299.  1349.  1349.5 1350.  1350.5 1351. 1449.  1450.5 1549.  1649.  1749.  1848.5 1849.  1948.5 1949.  2048.5. 2049. ]

Board Diagrams and ADC Codes：

sch&pcb.rar

  • 0
    TI__Guru 58981 points

    Hi Yivi Chan,

    I am confused about what you are trying to accomplish here: you want to both measure 50 Hz signals (presumably for metrology calculations on power lines), and also reject them? That doesn't really make any sense

    If you have unwanted frequencies in your system you need to identify how they are entering the system and find a way to filter them out, since you cannot rely on the ADC digital filter to remove them.

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 75 points

    Hi Bryan

    I am sorry that I failed to describe it clearly, let's forget the item of target signal for a moment and consider it as a noise for testing the ADC device, after designing the ADC test board we did some verification, when the ADC inputs were unconnected and the differential pairs were shorted with jumper wires the sampling revealed an odd harmonic of 50Hz, searching for the information I understand that this interference may come from space or power supply, I would like to hardware level to I want to eliminate or reduce this interference at the hardware level, is there any good recommended method.

    Best regards

  • 0 in reply to Bryan Lizon86
    Prodigy 75 points

    such as optimizing the ADC input front-end circuitry or redesigning the ADC driver power supply.

  • 0 in reply to Yivi Chan
    TI__Guru 58981 points

    Hi Yivi Chan,

    As mentioned, you need to identify how the noise is getting into your system and then somehow filter it out

    If I had to guess, it's probably coming in through the power supply, or coupling in through long cables. You might need to improve the PSRR of your supply

    Finally, you are showing a maximum of <2 LSB error in your plot, is this really worth considering? The ADC noise reported in the datasheet is always >4 LSB at the lowest data rate and gain = 1. So why are you worrying about <2 LSB?

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 75 points

    Thank you for your reply, we troubleshooted and found that it came from the power supply, after changing the supply frequency to 60hz, the harmonic frequency became an odd multiple of 60hz, the calculated SINAD was around 89dB, and the THD of the ADS131E08 was 93dB, which I think the test results are close enough to the manual.

    Best regards

  • 0 in reply to Yivi Chan
    TI__Mastermind 49565 points

    Hi Yivi Chan,

    Thanks for your update.

    BR,

    Dale