AFE5801: AFE 5801 SNR

GAGARIN BISWAL

Part Number: AFE5801

Hello,

I am using AFE5801. I am having doubt regarding SNR. As per datasheet signal is at -1dBFS and noise around somewhere at -100dBFS.

So SNR should have been 100 dB. But SNR given as 65.9dBFs.

Whether I am interpreting correctly? If I am wrong also give an idea how SNR is 65.9 dBFs.

Regards,

GBiswal

over 4 years ago

0 Chen Kung over 4 years ago

TI__Genius 12025 points

Hi,

Thanks for using AFE5801 device.

for your question:

This is noise density for 100dB.

After integrating BW, then we get 70dBFS SNR.

Thank you!

Best regards,

Chen

0 GAGARIN BISWAL over 4 years ago in reply to Chen Kung

Prodigy 110 points

Hello Chen,

Thanks for your reply.

If I am correct noise power = -100dB+10*log10(BW). Where 100 dB is the noise density.

But I am not sure what is the value of BW here.

Regards,

GBiswal

0 Xiaochen (Sean)Xu over 4 years ago in reply to GAGARIN BISWAL

TI__Expert 6040 points

GBiswal,

Noise density may not be exact accurate. actually it is the FFT BIN noise density.

in the datasheet, the plot is run at N point FFT, each bin is about Fs/N. then in your equation, the BW is that BIN size. Fs/N.

Thanks!

0 Chen Kung over 4 years ago in reply to Xiaochen (Sean)Xu

TI__Genius 12025 points

Hi,

Please refer to the AFE5801 Datasheet page 37

SNR = 10*Log10(PS/PN)

where PS=Power of Fundamental signal

PN=Power of total Noise

As you have seen from the plot, that is only one bin of the noise which is 100dBFS

(in this case)

Thank you!

Best regards,

Chen

0 GAGARIN BISWAL over 4 years ago in reply to Xiaochen (Sean)Xu

Prodigy 110 points

Hello Xiaochen,

Thanks for your reply.

Since it is not mentioned the number of FFT sample(N) in the datasheet, I was unable to calculate Fs/N.

Actually my doubt was whether BW to be considered as Fs/2 or Fs/N.

Regards,

GBiswal

0 Xiaochen (Sean)Xu over 4 years ago in reply to GAGARIN BISWAL

TI__Expert 6040 points

GBiswal,

it will be the Fs/N. The plot only showing the real part from 0 to Fs/2, the imagery part is -Fs/2.

for the SNR plot, you can refer to the AFE5801EVM user manual. there are calculation point as 64K points.

Thanks!

0 GAGARIN BISWAL over 4 years ago in reply to Xiaochen (Sean)Xu

Prodigy 110 points

Thank you very much.

Regards,

GBiswal

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AFE5801: AFE 5801 SNR