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.