How to make signal smooth using filter?
From what I can glance :

The chattering seems to be high-frequency compared to your signal of interest, it should not be hard to filter this chattering noise. You simply need to identify the frequency band of your signal and the frequency band of this noise. 

Could your perform an FFT to analyze the frequencies of your noise? Then design a filter that will not attenuate your signal of interest while attenuating the noise to an acceptable level.

Is it real-time processing or post-processing?