IIS3DWB bandwidth

SDiSt.1 · ‎2020-11-11

Hi,

The LPF2 filter on the IIS3DWB can set the cutoff frequency to ODR/4, ODR/10, ODR/20, etc. Figure 6 in the datasheet "Frequency response with LPF2 enabled" shows the bandwidth when LPF2 is set to ODR/4 to be 5.6 kHz. Is this correct? ODR/4 would put the cutoff at 26.67 kHz / 4 = 6.67 kHz. Does "ODR/4" simply describe the LPF2 stage and not the actual resulting bandwidth?

Thanks for your help,

Steve

Eleon BORLINI · ‎2020-11-12

Hi Steve @Community member ,

In theory you are right, in the sense that being ODR 26.667kHz, the ODR/4 should be 6.67 kHz.

However, consider the table in the datasheet p. 35, that refers to the sensor bandwidth resulting in a : the natural bandwidth after LPF1 (that cannot be excluded in the signal processing chain) is 6.3 kHz, that is the flatness of the frequency response is guaranteed up to this value, even if the actual ODR allows you to acquire also signals at higher frequencies, that will however result accordingly attenuated.

The combination ("sum") of the ODR/4 and this default bandwidth of 6.3kHz results in a 5.6kHz-effective band, while the "level 0" bandwidth doesn't affect sensitively the total bandwidth for lower low pass cut-off frequencies.

-Eleon

View solution in original post

Eleon BORLINI · ‎2020-11-12

Hi Steve @Community member ,

In theory you are right, in the sense that being ODR 26.667kHz, the ODR/4 should be 6.67 kHz.

However, consider the table in the datasheet p. 35, that refers to the sensor bandwidth resulting in a : the natural bandwidth after LPF1 (that cannot be excluded in the signal processing chain) is 6.3 kHz, that is the flatness of the frequency response is guaranteed up to this value, even if the actual ODR allows you to acquire also signals at higher frequencies, that will however result accordingly attenuated.

The combination ("sum") of the ODR/4 and this default bandwidth of 6.3kHz results in a 5.6kHz-effective band, while the "level 0" bandwidth doesn't affect sensitively the total bandwidth for lower low pass cut-off frequencies.

-Eleon

SDiSt.1 · ‎2020-11-13

That makes sense, thanks for your response Eleon.

Chubs · ‎2023-07-20

Hello @Eleon BORLINI,

What is the ODR when we enable the LPF2 in any of the given settings? The table 45 mentions the Bandwidth only.

We plan to use kNN-based denoising of MEMS sensor data & would like to have a maximum ODR of 26k Hz, however, we are trying to evaluate the practical benefits of model-based denoising wrt to LPF2 when selected for ORD/4 range.

I want to understand:

ODR calculations when LPF2 is enabled and disabled
How do we setup ODR/2 output from the MEMS sensor in case we plan to use the kNN-based denoising

Regards.

UPDATE:
IIS3DWB has a fixed ODR output at 26kHz. This cannot be changed. One can always decimate by discarding every 'n'th sample. However averaging in block sizr of 4 has been very valuable in terms of further noise reduction.

pb38 · ‎2023-09-15

Hello. You found the answer to your question about the ODR, you can not change it.

It is fixed around 26.7kHz and may vary with temperature (±2%).

It is not related to the way you setup internal filters.

Hope it helps