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ADS8881EVMV2-PDK: ADC Pro .txt file upload for FFT Analysis

Part Number: ADS8881EVMV2-PDK
Other Parts Discussed in Thread: ADS8881, MSP430FR5969

Hi,

I am currently working on a project that is comparing the ADC performance of the external ADC (ADS8881) and the internal 12b ADC of the MSP430FR5969. I am able to replicate the signal on the ADS8881EVM GUI.


As for the MSP430 12b ADC data, I upload it with the correct formatting into ADC Pro, where I do get a correct signal in the Multi Scope function (see attached)

But the problem that I am running into is running the FFT. My SNR performance is -1.76dB. Which I believe to be very low. (attached).

My input frequency is 6 Hz into the 12b internal ADC. Is there a reason for this poor performance? Is it related to my input signal or the data I have been receiving from the 12b ADC.

  

Thank you for the support!

Connor Connaughton

  • Hi Conner,

    Since the question is about the ADC12, you might consider talking with the MSP430 team as well.  You can see via the Scope plot that you have discontinuous data in your file - look around sample 325.  Something else seems to be wrong with your data set, if you are sampling a 6Hz signal at 100K, there's no way you could have ~15 cycles in 511 samples.  The period of a 6Hz sine wave is ~166mS and you are only displaying 5.11mS worth of data.  Looking at the FFT, it seems to think that your fundamental is ~3KHz, which fits the scope display.  If you take 511 samples with 15 cycles at 10uS, that works out to ~2935.421Hz.

    You need to make sure you have a proper dataset, based on what I can see in the scope capture above, the data in the FFT may actually be correct.

  • Hello Connor,

    Can you confirm your sample rate?  According to the above settings, you are sampling at 100ksps.  Based on the data you acquired, your input frequency is closer to 2.9kHz, not 6Hz.

    In order to capture 6Hz and get good FFT results, you will want to sample closer to 1ksps, and acquire at least 20000 samples.  In the FFT tab (below Stats), select the 7 Term Blackman-Harris Window.

    Also, your time domain data shows a discontinuity around sample 325.  This will definitely reduce SNR and THD measurements.

    Regards,

    Keith Nicholas
    Precision ADC Applications