High-pass filter in normal and reference mode(AN5201, IIS2DLPC), NEED a further explanation

[user1]

Details:

The high-pass filter can be configured in reference mode by setting the HP_REF_MODE bit in the CTRL7 register to 1. In this configuration the output data is calculated as the difference between the measured acceleration and the output values captured when reference mode was enabled. In this way only the difference is applied without any filtering. ​

Question & support:

1. It is required that the abscissa and ordinate in the figure represent the specific meaning, Can we think that the abscissa is the frequency and the ordinate is the amplitude
2. What is the output of the two modes? Can blue solid line be considered the output of filters or red dash line in figure 4?
3. The difference between the two modes cannot be seen from the figure. Can you provide further explanation? For example, specific input and output​

[Eleon BORLINI · Accepted solution]

Hi @user1​ ,

>> It is required that the abscissa and ordinate in the figure represent the specific meaning, Can we think that the abscissa is the frequency and the ordinate is the amplitude

Better to think that the abscissa is the time, and the vertical dashed line the instant in time at which the HP is enabled.

>> What is the output of the two modes? Can blue solid line be considered the output of filters or red dash line in figure 4?

The blue line is the output with the two modes applied, while the red one is the sensor output without filters applied.

>> The difference between the two modes cannot be seen from the figure. Can you provide further explanation? For example, specific input and output​

The main difference is that in the first case (high-pass filter mode) all the DC and low frequency components are ruled out from the data, while in the reference mode the value at the instant when reference mode was enabled is subtracted to the dataout of the device, keeping track of the DC and low frequency variations after that instant. This latter configuration could be used when the user is sure that a certain time during the acquisition there is no external contribution to the acceleration (or a reference, constant contribution) and so that value can be considered as a calibration value.

Check also this discussion, whether it can help you.

If my reply answered your question, please click on Select as Best at the bottom of this post. This will help other users with the same issue to find the answer faster. 

-Eleon