Digital

Logic AND Gate

AND-logic

Digital Logic AND Gate

Logic gates are the electronic circuits in a digital system that are mainly based on the Boolean function. Learn about AND, OR, XOR, NOT, NAND, NOR. The Logic AND gate is the type of digital logic in which have two or more than two inputs and one output, the operation of Logic AND gate is same as the multiplication rule. The output of logic AND is HIGH “1” when all inputs are HIGH and the output is LOW “0” when any of the inputs are LOW “0”. AND gate has many number of inputs but mostly uses 2 or 3 inputs. Let us understand the output of AND behaves with respect to two inputs:

logic multiplication of AND gate

It is a simple multiplication. Here you can see if any of the inputs is low the output will be low and when both inputs are high the output is high. The Boolean expression of AND logic that of for Logical Multiplication. It is denoted by a single dot or full stop symbol, ( . ) giving us the Boolean expression of AND gate A.B = Q. where “A” and “B” is the input of AND and “Q” is the output of AND logic.

                        “If both inputs ‘A’ and ‘B’ are true, then ‘Q’ is true”

 

2 Input AND Gate

The AND logic have two inputs and one output port

AND Gate Circuit Diagram

AND Gate Diode Circuit Diagram

The AND logic circuit can be design by diode and transistor, when the diode is use in AND logic circuit called diode AND gate, which is shown in below:

AND Gate Diode Circuit Diagram

The circuit diagram contains two diode inputs and one resistor. We applied power supply at “C”. When the both inputs is high the diode is reverse bias, it behaves an open circuit. The output is high. When any one of the diode input is low the low input diode is a forward bias diode and high input diode is reverse bias. The forward diode behaves like a short circuit, and due to short circuit the voltage are ground via forward bias diode and low output present at the output “X”.

2-input Transistor AND Gate

The transistor based AND gate contains two transistors and three resistors which is show in figure. The input terminal “A” and “B” and output terminal “Q”. for the high output “Q” both transistors must be saturated “ON”.

2-input Transistor AND Gate

Digital Logic “AND” Gate Types

The 2-input Logic AND Gate

The two inputs AND gate having two inputs “A” and “B” and output is “Q”.

The Boolean Expression of two inputs AND logic is Q = A.B

Symbol Truth Table

 

Logic AND Gate

2-input AND Gate

B A Q
0 0 0
0 1 0
1 0 0
1 1 1
Boolean Expression Q = A.B Read as A AND B gives Q

 

The 3-input Logic AND Gate

The three inputs AND having two inputs “A”, “B” and “C” output is “Q”.

The Boolean Expression of three inputs AND is Q = A.B.C

Symbol Truth Table

3-input AND Gate

3-input AND Gate

C B A Q
0 0 0 0
0 0 1 0
0 1 0 0
0 1 1 0
1 0 0 0
1 0 1 0
1 1 0 0
1 1 1 1
Boolean Expression Q = A.B.C Read as A AND B AND C gives Q

 

Multi-input AND Gate

The AND gate can be cascaded to obtained the multiple input for performing desired operation. However the commercial available AND gate IC’s having 2, 3, or 4-inputs packages. Below the figure show the cascaded AND logic;

Multi-input AND Gate

The Boolean Expression for this 6-input AND logic will therefore be:

Q = (A.B).(C.D).(E.F)

Commonly available AND gate IC’s of TTL and CMOS technologies:

Here full list of AND gate ICs based on TTL and CMOS technologies is given below:

S. No. IC NUMBER PURPOSE
1. 4073 Triple 3 -input AND
2. 4086 Expandable 4-wide, 2-input AND/OR invert (AOI)
3. 4085 Dual 2 -wide, 2 -input AND/OR invert (AOI)
4. 7409 quad 2 -input AND with open collector outputs
5. 741G08 single 2 -input AND
6. 741G09 single 2-input AND with open drain output
7. 7415 triple 3-input AND with open collector outputs
8. 7450 dual 2-wide 2-input AND-OR-invert
9. 7421 dual 4-input AND
10. 7411 triple 3-input AND
11. 7451 dual 2-wide 2-input AND-OR-invert
12. 7453 expandable 4-wide 2-input AND-OR-invert
13. 7452 expandable 4-wide 2-input AND-OR
14. 7455 2-wide 4-input AND-OR-invert
15. 7453 expandable 4-wide 2-input AND-OR-invert
16. 7454 4-wide 2-input AND-OR-invert
17. 7459 2-input and 3-input AND-OR-invert
18. 7458 2-input and 3-input AND-OR
19. 741G3208 single 3 input OR-AND
20. 74808 hex 2-input AND drivers
21. 74131 quad 2-input AND buffer with 15 V open collector outputs
22. 74130 quad 2-input AND buffer with 30 V open collector outputs

Apart from these IC’s there are some for our general applications. They are listed below.

CMOS Logic AND Gates

  • CD4081 Quad 2 –input
  • CD4082 Dual 4 –input
  • CD4073 Triple 3 –input 

TTL Logic AND Gates        

  •  74LS08 Quad 2-input
  •  74LS21 Dual 4-input
  •   74LS11 Triple 3-input

7048 Quad 2-input AND Gate IC

The Quad 2-input AND 7408 IC’s is shown below;

AND gate IC 7408 is a TTL series. Inside the IC has 4 AND gate. Each pin having own function which are explained below.

7048 Quad 2-input AND Gate IC

Pin number detail of IC 7048

Pin number detail of IC 7048

Pin 14 is supplied voltage pin. The maximum applied voltage is 5 volt DC; if we increase the supply voltage the IC may get damage.

4081 Quad 2-input AND Gate IC

The IC 4081 Quad 2-input AND is based on CMOS (complementary MOSFET). It has also 4 AND gate inside the IC. Now discuss the internal pin diagram of AND gate IC 4081:

4081 Quad 2-input AND Gate IC
Pin number detail of CMOS 4081 AND logic IC:

Pin number detail of CMOS 4081 AND IC

Pin 14 is supplied voltage pin. The maximum applied voltage is 5 volt DC; if we increase the supply voltage the CMOS IC 4081 may get damage.

AND gate Applications

There is a many application of AND logic in day to day life. Some applications are given below:

  • It use in enable and disable purpose on counter device
  • It is using in multiplexing of signal
  • It is uses in computer and communication system.
  • The logic AND is used in some sort of security devices like garden flood-lights and security lights etc.

Also read: Digital Logic Gates, Multiplexer,

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