In determining the polarity of such a circuit I used the following reasoning:
if Vin goes up ID1 goes up and ID2 goes down, ID4 goes down and VG3,VG4 go up because of PMOS, then Vout goes down, if Vout goes down then Vin will go up. So I ended up with positive feedback. Am I making a mistake? Sometimes when I try to understand a current source's relationship with its nodes polarities I get confused. Could you explain this point too?