[LIS3DSH] Anti-alias filter doubts

[mbertoni]

Hi to all users!

I have some doubts about LIS3DSH: I can set different ODR and different anti-alias filters.

What about filter? Is it digital? Analog? Which order?

I need to compare LIS3DSH noise (on shake table made for noise analysis for seismic purposes) with other cheaper MEMS accelerometers.

Usually I use an anti-alias digital filter on MCU but I would avoid to add code if anti-alias filter is already present on sensor, and at same time compare filters...

Anti-alias default value (800Hz) , so with ODR = 100 Hz I have no anti-alias filter, may you confirm?

Thanks.

[Eleon BORLINI]

Hi @mbertoni​ , the internal structure of the anti-alias filter of the LIS3DSH is not open... But I can share you the transfer function for different ODRs. The filter is a digital filter and its transfer function is shown in the below graph. Just to explain how the decimation filter works, for example taking into account that 4800/3 =1600 it means that, to obtain ODR=1600Hz starting from ADC samplig frequency of 4800Hz, the decimator executes an average of 3 samples of the same axis and then output the result or to obtain ODR=400Hz digital filter executes an average of 12 samples of the same axis before showing the result. Regards

[mbertoni]

Ok, so sampling frequency of LIS3DSH is 4800 samples per second.

I can select ODR value (CTRL_REG4).

Let's say I select ODR = 400Hz, so avarage of 12 samples (low-pass filter). Ok.

But what about CTRL_REG5? Is this an additional filter?

[Eleon BORLINI]

Yes, it is an additional filter working same way (digital filter), with the first notch pole at the frequency declared in the CTRL_REG5 (24h) register. Regards