Total delay will be due to 3 levels as above
- P&G generator
- Carry generator
- Sum Generator
P&G generator has a single level of EX-OR & AND gates they will work in parallel
delay1 =max(20,10) =20
Carry generator has a two levels AND + OR gates they will work one after another
delay2 =10+10 =20
Sum generator has a single level of EX-OR gates they will work all in parallel
delay3 =20
Total delay =delay1+delay2+delay3
20 + 20 +20 = 60ns