This document provides an overview of common logic gates and combinational logic circuits. It describes the basic functionality of inverters, AND gates, OR gates, NAND gates, NOR gates, XOR gates, and XNOR gates. Examples of their truth tables and applications are given. Combinational logic circuits like AND-OR logic and AND-OR-Invert logic are also discussed. The document shows how NAND gates and NOR gates can be used as universal gates to implement any logic function. It gives an example logic expression and shows its implementation using NAND gates and NOR gates.

1. Presentation
by
Suhair Subhan 20013322-004
Naeem Ullah 20013322-007
Hasnain Nazir 20013322-020
Abu Huraira 20013322-032

2. Contents
• The inverter
• The and gate
• The or Gate
• The nand gate
• The nor gate
• The XOR & XOR gate
• Basic combinational logic circuits
• Implementation of combinational logic circuit

3. Inverter
• The inverter (NOT circuit) performs the operation called inversion or
complementation.
• The inverter changes one logic level to the opposite level.
• In terms of bits, it changes a 1 to a 0 and a 0 to a 1.

4. Timing diagram of inverter
• When the input is LOW, the output is HIGH;
• when the input is HIGH, the output is LOW,
• thereby producing an inverted output pulse

5. Applications
• Figure 3 shows a circuit for producing the 1’s complement of an 8-bit
binary number.
• The bits of the binary number are applied to the inverter inputs
• and the 1’s complement of the number appears on the outputs.

6. And gate
• The AND gate is one of the basic gates that can be combined to form
any logic function.
• An AND gate can have two or more inputs and performs what is
known as logical multiplication.
• The AND gate is composed of two or more inputs and a single output,
as indicated by the standard logic symbols shown in Figure 4

7. Truth table
• An AND gate produces a HIGH output only when all of the inputs are
HIGH. When any of the inputs is LOW, the output is LOW.

8. application

9. Or gate
• An OR gate can have two or more inputs and performs what is known
as logical addition.
• For a 2-input OR gate, output X is HIGH when either input A or input B
is HIGH,
• when both A and B are HIGH; X is LOW only when both A and B are
LOW.

10. Application

11. Nand gate
• The term NAND is a contraction of NOT-AND and implies an AND
function with a complemented (inverted) output.
• It can be used as a universal gate; that is, NAND gates can be used in
combination to perform the AND, OR, and inverter operations.
•

12. Application

13. Nor gate
• The NOR gate, like the NAND gate, is a useful logic element because
• it can also be used as a universal gate; that is, NOR gates can be used
in combination to perform the AND, OR, and inverter operations.
• For a 2-input NOR gate, output X is LOW when either input A or input
B is HIGH, or when both A and B are HIGH; X is HIGH only when both
A and B are LOW.

14. application

15. XOR Gate
• Exclusive-OR and exclusive-NOR gates are formed by a combination of
other gates already discussed,
• For an exclusive-OR gate, output X is HIGH when input A is LOW and
input B is HIGH.
• when input A is HIGH and input B is LOW; X is LOW when A and B are
both HIGH or both LOW.

16. Application

17. XNor gate
• For an exclusive-NOR gate, output X is LOW when input A is LOW and
input B is HIGH,
• when A is HIGH and B is LOW; X is HIGH when A and B are both HIGH
or both LOW.

18. Combinational logic circuits
• combinational logic is a type of digital logic which is implemented by
Boolean circuits,
• where the output is a pure function of the present input only.
• In which the output depends not only on the present input but also
on the history of the input.

19. AND OR logic
• s an AND-OR circuit consisting of two 2-input AND gates and one 2-
input OR gate
• For a 4-input AND-OR logic circuit, the output X is HIGH (1) if both
input A and input B are HIGH (1) or both input C and input D are HIGH
(1).

20. And-or invert logic
• when the output of an AND-OR circuit is complemented (inverted), it
results in an AND-OR Invert circuit.
• For a 4-input AND-OR-Invert logic circuit, the output X is LOW (0)
• if both input A and input B are HIGH (1) or both input C and input D
are HIGH (1).

21. Implementation of combinational logic
• Logic expression
X = AB(CD + EF)

22. Nand gate as universal logic gate

23. Nor gate as a universal gate