NOR EXNOR

The circuit performs the two-input Exclusive NOR (XNOR) logic function using three-level NOR gates. When the input signals are different, either NOR gate U2 or NOR gate U3 is logic HIGH so the final output goes LOW. When the input signals are both logic HIGH, NOR gates U2 and U3 both generate logic LOW so the final output goes HIGH. When the input signals are both logic LOW, the output of NOR gate U1 becomes HIGH resulting to NOR gates U2 and U3 both generating logic LOW so the final output goes HIGH.