LSM6DSO analog anti aliasing

[adrianT]

Hi,

I would like to confirm if setting LSM6DSO ODR to 6.66KHz and LPF2 to ODR/10 (resulting to 666Hz bandwidth), then setting a FIFO decimation factor of 8 (resulting to 833hz FIFO ODR) will work in preventing aliasing for signals above 417Hz?

We have discovered with LSM6DSL that it doesn't work that well, but looking at a previous post where the LSM6DSO is recommended (Solved: LSM6DSL anti-aliasing filters do not appear to be ... - STMicroelectronics Community). So I would like to confirm it before we do a hardware change in production.

Thank you. 

[Federica Bossi]

Ciao @adrianT ,

LSM6DSO has effectively more performing filter like descripted in the other post.

Regarding your case using FIFO decimation of 8 result to a sampling frequency of 833 Hz while should be double respect signal bandwidth 2*ODR/10 = 1333 Hz. So I would suggest to use FIFO BatchDataRate of 4 to avoid aliasing.

Otherwise you can set LPF2 to have ODR/20 and leave sampling frequency with FIFO decimation of 8.

[adrianT]

Thanks for the confirmation. We determined that our setup can handle at most 1660Hz without requiring major changes in FW.

Would there be a difference in filtering performance (specifically in LPF for anti aliasing) if for example we just run the sensor in 1660hz ODR, no FIFO decimation and rely on LPF1 (ODR/2 = 833hz bandwidth)

compared to 6.6KHz ODR, FIFO decimation factor 4, LPF2 set to ODR/10 (Resulting to 666Hz bandwidth)

Both bandwidths are are acceptable in this case as we only need data right up to ~500hz. Anything above should be attenuated or at least not aliased back into the 0-500Hz data.