Sources of Variation: The primary sources of variation that necessitate derates are:
·PVT (Process, Voltage, Temperature) Variations: These are inter-chip variations.
o Process: Variations in manufacturing (e.g., lithography wavelength, defects) can alter transistor parameters like oxide thickness, dopant levels, and physical dimensions (W/L), which in turn affect threshold voltage (Vt) and current (I), and thus cell delay. Dies at the center of a wafer are more accurate than those at the periphery.