Half wave synchronous rectifier using MOSFET. MOSFET is on during negative half cycles as determined by the comparator, causing the negative half of the waveform to be shunted to ground.
Slight flaw in that switching signal breaks through via gate drain capacitance, only really a big issue with small signals, or where accuracy is paramount. The opamp buffer and the Rs & Cs are just a passive 3rd order lowpass filter.
