LSM6DSL anti-aliasing filters do not appear to be implemented despite setting appropriate registers according to the datasheet.

[ATzav.1]

I am using the LSM6DSL for a high frequency vibration measurement involving the accelerometer sensor only (gyroscope is turned off). Output data rates are variable between 400-3.3kHz. A recent frequency sweep experiment (0-6kHz applied on external speaker) with the 3.3kHz ODR in high performance mode, analog anti-aliasing filter bandwidth set at 1.5kHz and digital filter at ODR/2 as per the datasheet. In the resultant spectrogram, the frequency sweep signal aliases after crossing ODR/2, ODR, and 1.5*ODR multiple times over, with no obvious roll-off as would be expected with analog filter cutoff at 1.5kHz and digital filter at 1.66kHz. Forcing the analog filter to 400Hz and digital filter to ODR/4 does not seem to change anything.

These anti-aliasing filters at minimum ODR/2 should be active at all times, but this seems not to be the case. Is it possible that switching off the gyroscope might be causing issues with the enabling of these necessary filters? Similar aliasing has been noted in experiments with human voice harmonics.

[Eleon BORLINI]

HI @ATzav.1​ ,

We are analyzing your results.

Could you share the raw data of this spectrogram?

And are you getting the same results on other samples?

-Eleon

[Eleon BORLINI]

Hi @ATzav.1​ ,

I've submitted the spectrograms and the data to our expert, and they are currently evaluating them.

I'll get back to you as soon as I'll get a feedback from them.

-Eleon

[HAAA1]

Hi,

Are there any updates with regards to this @Eleon BORLINI​? If not, are there alternative IMUs we can use which don't have this issue? Thanks in advance and Happy New Year!

Best,

HA

[Eleon BORLINI]

Hi @HAAA1​ ,

Happy New Year to you too!

The LSM6DSL is actually quite an "old" product, and current state-of-the art devices such as the LSM6DSO(X) embeds an improved analog anti-alias filter in the acquisition chain (see p.28 of LSM6DSO datasheet, not so explicit it has been improved with respect to the elder one, actually).

 

-Eleon