I'm really confused with the representation of PMOS device shown in the figure. Since conventional current direction in PMOS is from source to drain, shouldn't the current source be pointing upwards(from node Y to VDD)?
Simplest way to remember current direction is by the little arrow indicator on the transistor, for NMOS it is pointing out of the drain thus current flows from source to drain. And for PMOS the arrow is into the source, so flows from source to drain. It is important to remember that the source is indicated by the arrow location. So in the case drawn, NMOS source is on the bottom and PMOS source is on the top.