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MMA8451Q: Impact of high-pass cut-off frequency on data

Question asked by tricon on Jun 23, 2015
Latest reply on Jul 15, 2015 by tricon

Dear Community!

 

We currently want to realize a project using the MMA8451Q where the following happenes (very simplified):

  • The accelerometer is in sleep-mode with a data-rate of 12.5Hz. Moreover, the transient acceleration detection is activated
  • When a transient acceleration is detected, it wakes up and switches it's data rate to 800Hz. Also the µC gets an interrupt from the accelerometer and the µC starts collecting high-pass filtered data from the accelerometer at 800Hz to search for the highest (transient) acceleration detected

 

My question is the following: When the accelerometer wakes up it switches its data rate dramatically from 12.5Hz to 800Hz. According to the datasheet of the MMA8451Q the high-pass cut-off frequency relates on the data rate. So it is changed on an transient acceleration event as well.

My feeling tells me that this can impact the high-pass filtered data collected right after the transient acceleration event (even for frequencies well beyond the cut-off frequency). Is this correct? Does the change of the cut-off frequency invalidate the first high-pass filtered data from the accelerometer after the transient acceleration event?

 

It would very be interesting for me how the high-pass is implemented within the accelerometer. Unfortunately, I did not find any information in the application notes.

 

Thanks for any help!

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