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Original question:

ADS8350: How is SNR Calculated in the DS?

ADS8350: Calculating Theoretical Noise Limit

Darren (FAE)
Expert 5483 points
Part Number: ADS8350

The ADS8350 datasheet lists SNR as 84dB.

I followed the following equations to calculate the internal ADC noise in Vrms

Given the 84dB from the DS, and the fact this was measured with Vref = 2.5V, using a -0.5dBFSR sine wave...

- Vsig_pp = 4.72V (-0.5dBFSR of 5Vpp sine wave)
- Vsig_rms = Vsig_pp / √2 = 3.34Vrms

Rearranging the SNR = 20LOG(Vsig/Vn) to find Vn_rms...I calculated:

Vn_rms = 210uVrms

Is this correct?

And this is considering the noise integrated across the full bandwidth (up to 1/2 the sampling frequency, which is 750kSPS)

Is this understanding correct?

EDIT: If the above is correct, and the internal noise of the ADC is 210uVrms, then if a smaller amplitude signal was input to the ADC, the SNR would appear worse, correct?

Regards,

Darren

  • 0
    TI__Guru 64226 points

    Hi Darren,

    Thank you for your post.

    There is a mistake in your calculations. Vrms is equal to Vpp / (2*sqrt(2)) = 1.67 Vrms. The noise will be 105.4 Vrms.

    The measured noise will include the total integrated noise over the full bandwidth of the ADC up until the Nyquist frequency, as you mentioned.

    Regards,