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MMA8451Q - Effective resolution calculation

Question asked by FABIO FILIPPA on Feb 16, 2018
Latest reply on Feb 20, 2018 by FABIO FILIPPA

Hi all,

I kundly ask about the effective resolution for this accelerometer model.

Suppose to work ad ODR=400 Hz hence BW=200 Hz.

 

From the device datasheet we have a PSD=99 ug/sqrt(Hz) @ 4g scale ODR=400 Hz

 

From the AN4075 the SNR(db) will be equal to:

  SNR(db)=20*log*(4g/(2sqrt(2)) / NRMS)

where:

  NRMS = PSD*SQRT(BW)=99u*SQRT(200)=1.4 mg

Hence:

  SNR(db)=60.087 dB

and finally we have for the bits number:

  n=(SNR(dB)-1.76)/6.02=9.68 bit

This means that instead of the theoretical 14 bit we have really usable 9 bit of resolution then 4g/2^9.68=4.87 mg of resolution.

 

Someone have carried out similar calculation?

 

Thanks in advance!

 

Best regards

Fabio

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