Hi,

as seen in the attached screenshot, three waveforms are displayed. The red one is basically the blue signal that has gone
though a high-pass filter (cutoff frequency at 5 Hz). It is a Sallen-Key filter whose amplifier is single-supplied, providing a
rail-to-rail of 0-5V. Knowing the HPF will decrease the impact of the DC offset and components up to around 5 Hz, it led to the
generation to some sort of a rectified half-wave. Could it be the result of the lower rail (0V) limitation, thwarting the other half of the wave from
swinging into the negative voltages? Basically, a self-created anomaly.

 

You operating the OpAmp single supply ? If so you need to bias it
properly.

Page 5 - http://www.ti.com/lit/an/sloa096/sloa096.pdf


Regards, Dana.

 

Yes, it's definitely because your op amp is incapable of swinging below its lower power supply rail. You need to bias it at 1/2 your positive supply voltage so it swings around the middle of its range and doesn't chop half the wave off.