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[ADXL354-ADXL355] Frequency response for seismic purposes

Question asked by Killertechno on Dec 5, 2017
Latest reply on Dec 11, 2017 by Killertechno

Hi to all, I don't know if someone would be already interested about using these MEMS accelerometers for seismic purposes (or has already done this).....
I have some doubts about frequency response.



page 3 of datasheet:

resonant frequency (1) = 2.4 kHz


(1) sensor characteristic [...] an analog 1.5kHz (-6dB) that cannot be bypassed limits actual output response


page 23 of datasheet:

The ADXL354/ADXL355 use an analog, low-pass, antialiasing filter to reduce noise and limit banwidth.

The ADXL355 provides further digital filtering options [...]

The analog, low-pass antialiasing filter [...] provides 1,5kHz bandwidth where output response is attenuated by 50%. The shape of filter response in the frequency domain is sinc3 filter.

So I understand both have got same internal low-pass filter, but in graphs shown in fig. 7, 8, 9 for ADXL354 shows 2400 Hz peak (I suppose resonance frequency), so without low-pass analog filter.....?????

1) I need poles and zeros to simulate frequency response of filter (usually seismic sensors have given poles and zeros from which  take out bode diagram for further analysis for compensation in terms of magnitude and phase). Is there a way to know parameters (poles and zeros) to do sensor simulation?



Talking about ADXL355:

Additional digital filtering [...] consist of low-pass digital decimation filter.
The first stage is fixed decimation filter with a 4kHz ODR with a low-pass filter cutoff (50% reduction in output response) at about 1kHz.

[...] second stage decimation filter is used for 2kHz output data rate and below [...]
Figure 60 shows the low-pass filter response with 1kHz corner (4kHz ODR) for ADXL355.

So first stage is decimation (low-pass) filter with sampling frequency of 4kSPS, I suppose the one in fig. 60 (not taking care of analog filter, right?), so why sampling frequency of fig. 60 looks like 20 kSPS?
I'm a bit confused.....

2) are there available digital filter (stage 1 and 2) coefficients or instructions to replicate model in Matlab?