cancel
Showing results for 
Search instead for 
Did you mean: 

[LIS3DSH] Anti-alias filter doubts

mbertoni
Associate II

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.

3 REPLIES 3
Eleon BORLINI
ST Employee

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

0693W000001q2C2QAI.png

mbertoni
Associate II

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?

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