I am designing buck converter in cadence and i have some problems with the mosfet switch when I add an ideal switches and check the switching waveform it looks ok "square wave with the desired duty cycle" but when I add the mosfets the waveform changes and I don't know why. attached the schematic and the waveform images
Looks like the PMOS transistor is slow to switch and the NMOS is not turning on.
What are the threshold voltages of the MOSFETs?
Changing the load resistor value has no effect?? It should have some effect.
The frequency of the MOSFET switching is not clear in the graphs. Can you check this and simulate again with frequencies in the order of 100kHz. Don't forget to change the load resistance. 0.4 ohm resistor may not be good idea with given C and L values here.
Iavg*V is of course right. The question is how much power is consumed by shoot-trough, simulataneous conduction of both MOSFETs. You may want to generate separate gate signals with deadtime.