Logic Circuits Pdf

Posted By admin On 13/01/22

@ 5 ˜3 ˆ )7ˇ ' 7 # A 1 B 1 C in C out Sum 1 ˆ ˘ ˆ C ˘ 13 AND2 12 AND2 14 OR3 11 AND2 ˘ ˝ ˆ 33 XOR 32 XOR A Sum C in out B 1-Bit Adder A 2 B 2 Sum 2 0 C in C out. These logic circuits are made of various logic gates, by connecting them in certain combinations, in order to produce the required output.Digital logic circuits are mainly classified into two types, sequential logic circuits and combinational logic circuits. This article gives a brief idea about the combinational logic circuits.

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Logic gates are the basic building blocks of any digital system. It is an electronic circuit having one or more than one input and only one output. The relationship between the input and the output is based on a certain logic. Based on this, logic gates are named as AND gate, OR gate, NOT gate etc.

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

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

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.

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Logic diagram

Truth Table

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

LOGIC CIRCUITS Questions :-

1. What is a combinational circuit?

In a combinational circuit, the output depends upon present input(s) only i.e, not dependant on the previous input(s). The combinational circuit has no memory element. It consists of logic gates only.

2. Write two characteristics of combinational circuits.

The two characteristics of combinational circuits are:

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  1. In combinational circuits, the output exists as long as the input exists.
  2. A combinational circuit will always respond in the same fashion to the input function, when we apply signal to the input terminal of the combinational logic circuit.

3. What is a half-adder?

A logic circuit, that can add two 1-bit numbers and produce outputs for sum and carry, is called a half-adder.

4. What is a full-adder?

A binary adder, which can add two 1-bit binary numbers along with a carry bit and produces outputs for sum and carry is called a full-adder.

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5. What is a flip-flop?

A flip-flop is a basic memory element that is made of an assembly of logic gates and is used to store 1-bit of information.

6. Explain what is a latch?

It is a D-type of flip-flop and stores one bit of data.

Simplifying

7. Explain what is an excitation table?

Excitation table gives an information about Explain what should be the flip-flop inputs if the outputs are specified before and after the clock pulses.

8. Explain what is a state table?

State table consists of complete information about present state, next state, and outputs of a sequential circuit.

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