In an avanced way This circuit is the first step of anyway digital device. It is an Analog voltage follower that save for a time the Analog value to allow the A/D conversion stage (or whatever there will be) to work well, because it needs time to read.
There is a compensated voltage divider that is ever seen the same, never change by the input, in fact the MOSFETs work in a complementary way.
The final capacitor is the memory of the circuit.
