TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New

Delhi-75Affiliated Institution of G.G.S.IP.U, Delhi

DIGITAL ELECTRONICSPaper Code :- BCA 106

Keywords:Logic Gates, AND, OR, NOR, NAND

By :-HARI MOHAN JAIN

TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New Delhi-75

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Logic Gates

TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New Delhi-75

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Logic Gates

• The building blocks used to create digital circuits are logic gates

• There are three elementary logic gates and a range of other simple gates

• Each gate has its own logic symbol which allows complex functions to be represented by a logic diagram

• The function of each gate can be represented by a truth table or using Boolean notation

TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New Delhi-75

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• The AND gate

• The AND gate has the following symbol and truth table.

• Two or more input bits produce one output bit.

• Both inputs must be true (1) for the output to be true.

• Otherwise the output is false (0).

TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New Delhi-75

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• The OR gate

• The OR gate has the following symbol and truth table.

• Two or more input bits produce one output bit.

• Either inputs must be true (1) for the output to be true.

TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New Delhi-75

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• The NOT gate (or inverter)

• The simplest possible gate is called an "inverter" or a NOT gate.

• One bit as input produces its opposite as output.

• The symbol for a NOT gate is shown below.

• The truth table for the NOT gate shows input and output.

TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New Delhi-75

7What happens when you add a NOT to an AND gate?

“Not AND” = NAND A B X

0 0 1

0 1 1

1 0 1

1 1 0

TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New Delhi-75

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• The NAND gate

TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New Delhi-75

9What happens when you add a NOT to an OR gate?

“Not OR” = NORA B X

0 0 1

0 1 0

1 0 0

1 1 0

TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New Delhi-75

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• The NOR gate

TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New Delhi-75

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• The Exclusive OR gate

• Exclusive OR gate are true if either input is true but not both.

• The Symbol and Truth Table is shown below.

• Output will be high for different inputs

TRINITY INSTITUTE OF PROFESSIONAL STUDIESSector – 9, Dwarka Institutional Area, New Delhi-75

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• The Exclusive NOR gate

• The Symbol and Truth Table is shown below.

• Output will be high for same inputs