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Why the SNR in spectral analysis doesn't match with the spec of ADS8860 (SAR ADC PDK EVM & GUI)

Willy Chen10
Prodigy 220 points

HI,

i have one question when using SAR ADC PDK EVM and Plabs Toolkit.

The SNR of ADS8660 is only about 93db.

but why the figure of the spectral analysis shows that the noise floor is about 130dB~140dB

Here's my test result with coupon1(Good Filter1) of SAR ADC PDK EVM

why the red block doesn't match with the yellow block?

Thank you!

Regards,

Willy

  • 0
    TI__Mastermind 24970 points

    Hello Willy,

    I would suggest watching the AC Specification Video in the TIPrecision Labs-ADC series. It will give you a better understanding of what these parameters and specifications mean.

    For a short explanation, the yellow and red box are not meant to match. The red box indicates where the noise floor lies, the lower the better. Note that the noise is not a straight line, it varies through the frequency spectrum, thus you have to take the total noise, not just a measured point to calculate the SNR. The yellow, which is the SNR of the device shows the ratio between the total noise and the input signal. You can see this output change if you change the amplitude of your input signal, you will also see that the noise floor (if nothing else is changed) should remain the same. The large the noise the higher the SNR, and vice versa.

    Regards

    Cynthia