4 input NOR gate

Construction of PDN :

The PDN of 4 input NOR gate is shown in Figure below. It consists of parallel combination of 4 NMOS transistors that conducts when any of the input is high and pulls the output F to logic low.

Construction of PUN :

The PUN is dual of PDN and it consists of series combination of four PMOS transistor as shown in Figure below.

Construction of 4 input NOR gate :

The complete CMOS NOR gate is shown in Figure below which is combination of PUN and PDN.