Logic gates

3. AND Gate
A circuit which performs an AND operation is shown in figure. It has n input
(n >= 2) and one output.
Logic diagram Truth Table
OR Gate
A circuit which performs an OR operation is shown in figure. It has n input
(n >= 2) and one output.
Logic diagram Truth Table

4. NOT Gate
NOT gate is also known as Inverter. It has one input A and one output Y.
Logic diagram
Truth Table
NAND Gate
A NOT-AND operation is known as NAND operation. It has n input (n >= 2) and one output
Logic diagram
Truth Table
NOR Gate

5. NOR Gate
A NOT-OR operation is known as NOR operation. It has n input (n >= 2) and one output.
Logic diagram
Truth Table
XOR Gate
XOR or Ex-OR gate is a special type of gate. It can be used in the half adder, full adder and subtractor. The
exclusive-OR gate is abbreviated as EX-OR gate or sometime as X-OR gate. It has n input (n >= 2) and one
output.
Logic diagram Truth Table

6. XNOR Gate
XNOR gate is a special type of gate. It can be used in the half adder, full adder and subtractor.
The exclusive-NOR gate is abbreviated as EX-NOR gate or sometime as X-NOR gate.
It has n input (n >= 2) and one output.
Logic diagram
Truth Table

7. 2 INPUT NAND gate
A A A B
0 0 1
0 1 0
1 0 0
1 1 1
EXNOR Gate
The 'Exclusive-NOR' gate circuit does the opposite to the EOR gate. It will
give a low output if either, but not both, of its two inputs are high. The symbol is
an EXOR gate with a small circle on the output. The small circle represents
inversion.
Schematic Symbol Truth Table
A B
ENOR
Example:

9. Block diagram

10. Below is an example of 2 input combined logic gates, now let us find the
output function for this circuit.
Truth Table Schematic Diagram
A B Q
0 0
0 1
1 0
1 1
AB
1st AND
2ndAND
OR
1st NOT
2nd NOT
AB
 First draw a 2 input truth table.
 Second let us identify the different logic gate used in the circuit. We have 2
AND gate, 2 NOT gate, and 1 OR gate.
 Third let us find the output function for the 1st combination in the truth table
A=0 and B=0.
 Input A & B goes to the 1st AND gate then have an output of0
Truth table for 1st
AND
 Input A goes to 1st NOT gate and becomes 1; input B goes to 2nd NOT gate
and becomes 1 then the inverted A & B goes to 2nd AND gate and have an
output of 1
Truth table for 2nd
AND, take note that
the inputs are inverted

11.  The output of 1st and 2nd AND gate goes to OR gate and then will have an output function of 1.
 Then the output function for Input A=0 and B=0 for this circuit is 1.
 Write the output on the truth Table.
 Repeat same process on the 2nd, 3rd, and 4th Input.
A B Q
0 0 1
0 1 0
1 0 0
1 1 1
2ndAND
OR
1stAND