FPGA based unknown circuit application

[mo.glmdi]

Hello Everyone.
I'm analyzing a piece of circuit that have FPGA in its core to understand its operation. But I've encountered a part of this circuit that I have no idea about it. There is an input signal from a pick-up coil with 2.5V offset DC after amplification stage and a comparator that compare this signal with a 2.5VDC reference voltage and outputs a pulse train that just fluctuate like a noise. I'm wondering what is the main idea behind this section? Is it for noise removal? If yes, What is the main algorithm to do this?
I attached the schematic of circuit in this post and really appreciate if anyone can help me to resolve this problem.   

[hamster_nz]

This is most likely the error signal in a control loop. The signal is ikely to be samples and filtered to generate the error term..

[mo.glmdi]

Thanks @hamster_nz . I think so. It can be an error predicting routine for removing error or noises and finally reaching higher resolutions in pick-up coil signal. But I have no idea about existing algorithms and methods. Do you have any thought about methods of such control loop? 

[SiliconWizard]

You may or help us figure out what this signal is for if you told us what this coil is picking up exactly. Maybe a partial schematic or something.