Made Easy Test Series, Digital logic

Question

Q) The sum of product (SOP) form of logic expression is most suitable for designing logic circuit using only

A.) AND gates

B.) NAND gates

C.) EX-OR gates

D.) NOR gates

Comments

we can build SOP circuit which is AND OR realization. which can be converted to NAND-NAND.

Hence B) NAND gates is correct

Answer 1

NAND and NOR are called universal gates because all the other gates like AND,OR,NOT,XOR and XNOR can be derived from it.

With either NOR or NAND we can design  any circuit. Means either POS or SOP  form of logic expression can be design by both NOR or NAND gate but here we are talking about most suitable(less gate required or we can say no extra Gate using ).

when you use SOP form, no.of NAND gates less compared to NOR

due to Sum of Products = AND ( 1st level ) - OR ( 2nd level ) realization = NAND - NAND

 

when you use POS form, no.of NOR gates less compared to NAND

due to Products of Sums = OR ( 1st level ) - AND ( 2nd level )  realization = NOR - NOR

so we can say

• In SOP we have AND-OR so here we can replace it with NAND-NAND.
• In POS we have OR-AND so here we can replace it with NOR--NOR.

for more details:- http://www.asic-world.com/digital/gates3.html