BHAGWATI INTERNATIONAL PUBLIC SCHOOL Dr. Indu Dayal Meshri Primary English School
INVESTIGATORY PROJECT ON “ Logic Gates ”
Guided by: - Mr. Sandeep Darji Submitted by: - Rohan .D. Patel Roll no: -
This is to certify that Mr. Rohan Patel student of XII science Roll no ___________worked on project titled“Logic Gates” held in Bhagwati International Public School during the academic year 2016-2017. He worked sincerely under the guidance of faculties and prepared this dissertation.
External Teacher
Principal
Subject Teacher
ACKNOWLEDGEMENT First of all, I am immensely indebted to almighty god for his blessings and grace without which I could not have undertaken this task and my efforts would never have been a success. I humbly consider a privilege and honor to express my heartiest and profound gratitude to Mr. Rajendra.S. Malwal, principal BIPS, Patan. For his appropriate direction, valuable suggestion, under judging assistance so generously extended to me. I wish to express my deepest feelings of gratitude to Mr. Sandeep Darji, physics department, BIPS Patan. For his erudite involvement and sustained guidance which has been pivotal in my project work. His minute observation, precious insights, critical comments have indeed greatly helped to shape my ideas. This guidance and support received from my entire classmates who contributed and who are contributing to this project, is vital for the success of this project. I am grateful for their constant support and help. I also owe sense of gratitude to my parents for encouragement and support throughout the project.
- ROHAN PATEL
Content’s. Sr.no
Title
Page no.
1
Introduction
1
2
Principle
2
3
Basic Gates
3
4
The OR Gate
5
5
The AND Gate
7
6
The NOT Gate
9
7
The NOR Gate
11
8
The NAND Gate
13
9
The EX-OR Gate
15
10
The EX-NOR Gate
17
11
Conclusion
19
12
Bibliography
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Introduction. GATE: - A gate is defined as a digital circuit which follows some logical relationship between the input and output voltages. It is a digital circuit which either allows a signal to pass through or stop it.  The logic gates are building blocks at digital electronics. They are used in digital electronics to change one voltage level into another according to some logic statement relating to them.
Truth Table: - A logic gate may have one or more than one inputs, but it has only one output. The relationship between the possible values of input and output voltages are expressed in the form of a table called truth table.  Truth table of a logic gate is a table that shows all the inputs and outputs that are possible for the logic gates.
Boolean Algebra: - The algebra which is based on binary nature of the logic gates.
Boolean Expressions: - They are the logical statement which are followed by logical gates.
1
Principle. Any Boolean algebraic operation can be associated with the input and output, which represents the statement of Boolean algebra. Although these circuits may be complex, they may all be constructed from three basic devices like a P-N junction diode, a resistance and a N-PN transistor. We have three different type of logic gates and they are the AND gate, the OR gate and the NOT gate.
LOGICAL STATEMENTS. 1
0
High
Low
Positive
Negative
On
Off
Close
Open
Conducting
Non-Conducting
Right
Wrong
True
False
Yes
No
2
Basic Gates. The OR Gate: - It is a device that combines A and B to give Y as the result. The OR gate has two or more inputs and one output. In Boolean algebra, addition symbol (+), is referred as the OR. The Boolean expression: A+B=Y This indicates that Y equals to A or B.
The AND Gate: - It is a device that combines A with B to give Y as the result. The AND gate has two or more inputs and one output. In Boolean algebra, multiplication sign is referred as the AND. The Boolean expression: A.B=Y or A X B=Y This indicates that Y equals to A and B.
3
The NOT Gate: - It is a device that inverts the inputs. The NOT has one input and has one output. In Boolean algebra, bar symbol is referred as the NOT. ̅=𝒀 The Boolean expression: 𝑨 This indicates that Y is not equal to A.
- Making of logic gates was started by binary numbers. - Logic gates can also store information.
4
The OR Gate. Aim: To design and stimulate the OR gate circuit.
Components: Two ideal p-n junction diode (D1 and D2).
Theory and Construction: An OR gate can be realized by the electronic circuit, making use of two diodes D1 and D2.
Hear the negative terminal of the battery is grounded and corresponds to the 0 level, and the positive terminal of the battery corresponds to level 1. The output Y is voltage at C with respect to earth.
5
The following conclusion can be drawn from the above circuit: (i)
If the switch A and B are kept open (A=1, B=0), then bulb does not glow, hence Y=0 If switch A is kept closed and B is kept open (A=1, B=0), then bulb does not glow, hence Y=0 If switch A is kept open and B is kept closed (A=0, B=1), then bulb does not glow, hence Y=0 If switch A and B both are kept closed (A=1, B=1), then bulb glows, hence Y=1
(ii)
(iii)
(iv)
TRUTH TABLE: Input A
Input B
OUTPUT
0
0
0
0
1
0
1
0
0
1
1
1
6
The AND Gate. Aim: TO DESING AND STIMULATE THE AND GATE CIRCUIT.
Components:  Two ideal p-n junction diode (D1 and D2)  A resistance R.
Theory and Construction: An AND gate can be realized by the electronic circuit, making use of two diodes D1 and D2. The resistance R is connected to the positive terminal of a 5V battery permanently.
Here the negative terminal of the battery is grounded and corresponds to the 0 level, and the positive terminal of the battery corresponds to the level 1. The output Y is the voltage at C with respect to earth.
7
The following conclusion can be easily drawn from the working of this circuit: (i) (ii)
(iii)
(iv)
If the switch A and B are kept open (A=0, B=0), then bulb does not glow., hence Y=0. If switch A is kept closed and B is kept open (A=1, B=0), then bulb does not glow, hence Y=0. If switch A is kept open and B is kept closed (A=0, B=1), then bulb does not glow, hence Y=0. If both switch A and B are kept closed (A=1, B=1), then bulb glows, hence Y=1.
TRUTH TABLE: Input A
Input B
OUTPUT
0
0
0
0
1
0
1
0
0
1
1
1
8
The NOT Gate. Aim: TO DESIGN AND STIMULATE THE NOT GATE CIRCUIT.
Components: An ideal n-p-n transistor.
Theory and Construction: A NOT gate cannot be realized by using diodes. However, an electronic circuit of NOT gate can be realized by making use a n-p-n transistor.
The base of the transistor is connected to the input A through a resistance Rb and the emitter is earthed. The collector is connected to 5V battery. The output Y is voltage at C with respect to earth.
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The following inference can be easily drawn from the working of circuit: (i) (ii)
If the switch A is kept open(A=0) then bulb glows, hence Y=1 If the switch A is kept closed(A=1) then bulb does not glow, hence Y=0
TRUTH TABLE: Input A
OUTPUT Y
0
1
1
0
10
The NOR Gate. Aim: TO DESIGN AND STIMULATE THE NOR GATE CIRCUIT.
Component:  Two ideal p-n junction diode (D1 and D2).  An ideal n-p-n transistor
Theory and Construction: If we connect the output Y’ of OR gate to the input of a NOT gate, then the gate obtained is the NOR gate. The output Y is voltage at C with respect to earth.
11
In Boolean expression, the NOR gate is expressed as: (𝑦 = ̅̅̅̅̅̅̅̅ 𝐴 + 𝐵) And is being read as “A or B negated”.
Th following inference can be easily drawn from the working of electrical circuit: (i) (ii)
(iii)
(iv)
If the switch A and B is kept open (A=0, B=0) then bulb glows, hence Y=1. If the switch A is kept closed and B is kept open (A=1, B=0) then the bulb glows, hence Y=0. If the switch A is kept open and B is kept closed (A=0, B=1) then the bulb does not glow, hence Y=0. If the both switch A and B are kept closed (A=1, B=1) then bulb does not glow, hence Y=0.
TRUTH TABLE: Input A
Input B
OUTPUT
0
0
1
0
1
0
1
0
0
1
1
0
12
The NAND Gate. Aim: TO DESIGN AND STIMULATE THE NAND GATE CIRCUIT.
Components:  Two ideal p-n junction diode(D1 and D2)  A resistance R  An ideal n-p-n transistor
Theory and Construction: If we connect the output Y’ of the AND gate to the input of a NOT gate then the gate obtained is the NAND gate. The output Y is voltage at C with respect to earth.
13
In Boolean expression, the NAND gate is expressed as: (𝑦 = ̅̅̅̅̅ 𝐴. 𝐵 ) And is being read as ‘A and B negated’.
The following inference can be easily drawn from the working of circuit: (i) (ii)
(iii)
(iv)
If the switch A and B are kept closed (A=0, B=0) then bulb glows, hence Y=1. If the switch A is kept open and B is kept closed (A=0, B=1), then bulb glows, hence Y=1 If switch A is kept closed and B is kept open (A=1, B=0), then bulb glows, hence Y=1 If both switch A and B are kept closed (A=1, B=1) then bulb does not glow, hence Y=0.
TRUTH TABLE: Input A
Input B
OUTPUT
0
0
1
0
1
1
1
0
1
1
1
0
14
The EX-OR Gate. Aim: TO DESIGNA AND STIMULATE THE EX-OR GATE CIRCUIT.
Components:  Two AND gates  An OR gate  Two NOT gate
Theory and Construction: The operation EX-OR checks for the exclusivity in the value of the two signals A and B. It means if A and B are not identical, the output Y=1, and if both are identical, then output Y=0. This operation is also called exclusive OR gate, designated EX-OR.
15
In Boolean expression, the EX-OR gate is expressed as: (𝑦 = 𝐴 ⋅ 𝐵̅ + 𝐴 ⋅ 𝐵 = 𝐴 ⊕ 𝐵)
The following inference can be easily drawn from the working of electrical circuit: (i) (ii)
(iii)
(iv)
If the switch A and B are kept open (A=0, B=0) then bulb does not glow, hence Y=0 If the switch A is kept open and B is kept closed (A=0, B=1) then bulb glows, hence Y=1 If the switch A is kept closed and B is kept open (A=1, B=0) then the bulb will glow, hence Y=1 If the switch A and B are kept closed (A=1, B=1) then bulb will not glow, hence Y=0
TRUTH TABLE: Input A
Input B
OUTPUT
0
0
0
0
1
1
1
0
1
1
1
0
16
The EX-NOR Gate. Aim: TO DESIGN AND STIMULATE THE EX-NOR GATE CIRCUIT.
Components:  Two AND gates  And OR gate  Three NOT gates
Theory and Components: The operation EX-NOR checks for the exclusively in the value of the two signals A and B. it means if A and B are not identical, the output Y=0, and if both are identical, then the output Y=1. This operation is also called exclusive NOR gate, designated EX-NOR.
17
In Boolean expression, the EX-NOR gate is expressed as (𝑦 = 𝐴 ⋅ 𝐵̅ + 𝐴̅ ⋅ 𝐵 = ̅̅̅̅̅̅̅̅ 𝐴 ⊕ 𝐵)
The following inference can be easily drawn from the working of electrical circuit: (v)
If the switch A and B are kept open (A=0, B=0) then bulb glows, hence Y=1 (vi) If the switch A is kept open and B is kept closed (A=0, B=1) then bulb does not glow, hence Y=0 (vii) If the switch A is kept closed and B is kept open (A=1, B=0) then the bulb does not glow, hence Y=0 (viii) If the switch A and B are kept closed (A=1, B=1) then bulb will glow, hence Y=1
TRUTH TABLE: Input A
Input B
OUTPUT
0
0
1
0
1
0
1
0
0
1
1
1
18
Conclusion. Logic gates are used to develop many IC circuits or microchips in today’s modern world. NAND gate and NOR gate are known as universal gates because we can construct all the three basic gates using NAND & NOR gates.
Without logic gates, electronic world would be nearly incomplete!
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Bibliography. This project would be nearly incomplete if I had not used the information given in the following websites. My special thanks to the uploader of information on these websites. If considered, I have used everything that GOOGLE shows me…….
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