This document introduces digital logic circuits, including combinational and sequential circuits. It discusses that combinational circuits contain only logic gates and their output depends solely on present inputs. Sequential circuits contain both logic gates and memory elements, so their output depends on present inputs and previous states. The document outlines the design and analysis procedures for combinational circuits and provides examples of their block diagrams. It also describes synchronous and asynchronous sequential circuits.

2. DIGITAL LOGIC CIRCUITS
~ INTRODUCTION TO COMBINATIONAL AND
SEQUENTIAL CIRCUITS.
~DESIGN PROCEDURE OF COMBINATIONAL
CIRCUITS
~ANALYSIS PROCEDURE OF COMBINATIONAL
CIRCUITS
PRESENTED BY:
QURATULAIN
BS(CS)-1
QUAID-E-AZAM UNIVERSITY
ISLAMABAD ,PAKISTAN.

3. TYPES OF DIGITAL LOGIC
CIRCUITS
 COMBINATIONAL CIRCUITS
 SEQUENTIAL CIRCUITS

4. COMBINATIONAL CIRCUITS
 Combinational Circuits are made of logic
gates.
 Doesn’t contain memory element , that’s
why they cant store any information.
 Value of present output is determined by
present input.
 Examples of combinational circuits are
half adders, full adders, sub tractors etc.

5. BLOCK DIAGRAM OF A
COMBINATIONAL CIRCUIT

6. SEQUENTIAL LOGIC CIRCUITS
 Made up of combinational circuits and
memory elements.
 These memory elements are devices
capable of storing ONE-BIT information.
 Output depend on input and previous
state.
 Examples of sequential circuits are flip
flops, counters, shift registers

7. BLOCK DIAGRAM OF A
SEQUENTIAL CIRCUIT

8. TYPES OF SEQUENTIAL
CIRCUITS
Sequential circuits are of two types:
1.SYNCHRONOUS CIRCUITS:
 In synchronous sequential circuits, the state
of the device changes only at discrete times
in response to a clock Pulse.
2.ASYNCHRONOUS CIRCUITS:
 Asynchronous circuit is not synchronized by
a clock signal; the outputs of the circuit
change directly in response to changes in
Inputs.

9. DESIGN PROCEDURE OF
COMBINATIONAL CIRCUITS
This procedure involves the following
steps:
 The problem is stated.
 The number of available input
variables and output variables is
determined.
 The input and output variables are
assigned letter symbols.
 Truth table is drawn
 Boolean function for output is obtained.

10. ANALYSIS PROCEDURE OF
COMBINATIONAL CIRCUIT
 TO DETERMINE THE OUTPUT FUNCTIONS
AS ALGEBRAIC EXPRESSIONS.
 It is the reverse process of design procedure.
 Logic diagram of the circuit is given.
 Obtain the truth table from the diagram.
 Obtain Boolean function from the Truth Table
for output.

11. LOGIC DIAGRAM FOR
ANALYSIS EXAMPLE:

12. THE CIRCUIT HAS THREE
INPUTS, A,B,C
AND TWO OUTPUTS F1 AND F2
 The Boolean function for outputs are:
F2=AB+AC+BC
T1=A+B+C
T2=ABC
 Outputs functions for gates are :
T3=F2’T1
F1=T3+T2

13. Substituting and simplifying, we get :

14. TRUTH TABLE DRAWN FROM
THE LOGIC DIAGRAM.

15. BOOLEAN FUNCTIONS
OBTAINED FOR OUTPUT ARE :
 F2=AB+AC+BC
 F1=A’BC’+A’B’C+AB’C’+ABC