PVT variation means variations in process, voltage and temperature. Process parameters variations in the integrated circuit could be deviation in oxide thickness, diffusion depth or impurity concentration. These variations could occur due to variations in the manufacturing conditions. Process parameters variations could be seen throughout the chip. As a consequence, each transistor has different transistor lengths throughout the chip. Thus propagation delay becomes different everywhere in chip. There can be deviation in the given value of supply voltage.

Variation in supply voltage too varies the propagation delay throughout the chip. Temperature variation does happen throughout the chip. This is primarily because of power dissipation in the MOSFETs. Majority of power in MOS IC is dissipated during switching event. This is the time when both NMOS and PMOS transistors are conducting. This dissipated power contribute temperature rise. The mobility of electrons and holes depends on the temperature. So, when the electrons and holes move slower. It increases the propagation delay. Thus propagation delay increases with increases temperature.