Digital Logic

• A universal gate is a gate which can implement any Boolean function without need to use any other gate type.
• The NAND and NOR gates are universal gates. 

 

• A NAND gate represents the complement of the AND operation. Its name is an abbreviation of NOT AND.
• The graphic symbol for the NAND gate consists of an AND symbol with a bubble on the output, denoting that a complement operation is performed on the output of the AND gate.
• Figure below illustrates the truth table and graphical symbol of NAND gate :

By this truth table, we can construct a logic gate :

 Implementing an Inverter Using only NAND Gates 

1. All NAND input pins connect to the input signal A gives an output A’. 
2. One NAND input pin is connected to the input signal A while all other input pins are connected to logic 1. The output will be A’.  

Implementing AND Using only NAND Gates 

An AND gate can be replaced by NAND gates (The AND is replaced by a NAND gate with its output complemented by a NAND gate inverter).

Implementing OR Using only NAND Gates 

An OR gate can be replaced by NAND gates (The OR gate is replaced by a NAND gate with all its inputs complemented by NAND gate inverters).

Thus, the NAND gate is a universal gate since it can implement the AND, OR and NOT functions.

 

• A NOR gate represents the complement of the OR operation. Its name is an abbreviation of NOT OR.
• The graphic symbol for the NOR gate consists of an OR symbol with a bubble on the output, denoting that a complement operation is performed on the output of the OR gate.
• Figure below illustrates the truth table and graphical symbol of NOR gate :

Implementing an Inverter Using only NOR Gates

1. All NOR input pins connect to the input signal A gives an output A’. 
2. One NOR input pin is connected to the input signal A while all other input pins are connected to logic 0. The output will be A’.

Implementing OR Using only NOR Gates 

An OR gate can be replaced by NOR gates (The OR is replaced by a NOR gate with its output complemented by a NOR gate inverter)

Implementing AND Using only NOR Gates 

An AND gate can be replaced by NOR gates (The AND gate is replaced by a NOR gate with all its inputs complemented by NOR gate inverters)

Thus, the NOR gate is a universal gate since it can implement the AND, OR and 

NOT functions. 

Published by :

NUR AKMALIZA BT ZANURY

B031310303