Dual 4-Input AND Gates



To study and verify the truth table of Dual 4-Input AND Gates

Learning Objectives

  1. To understand the behavior and demonstrate the operation of Dual 4-Input AND Gates
  2. To apply knowledge of the fundamental gates to create truth tables.
  3. To develop digital circuit building and troubleshooting skills.
  4. To understand key elements of TTL logic specification or datasheets.

IC Used

For Dual 4-Input AND Gates:
IC NumberIC Name
74LS21Dual 4-Input AND Gates

Circuit Tutorials:


  1. Place the IC on IC Trainer Kit.
  2. Connect VCC and ground to respective pins of IC Trainer Kit.
  3. Implement the circuit as shown in the circuit diagram.
  4. Connect the inputs to the input switches provided in the IC Trainer Kit.
  5. Connect the outputs to the switches of O/P LEDs
  6. Apply various combinations of inputs according to the truth table and observe the condition of LEDs.
  7. Note down the corresponding output readings for various combinations of inputs.
  8. Power Off Trainer Kit, disconnect all the wire connections and remove IC's from IC-Base.


AND GATE - ​ It is a digital circuit that has two or more inputs and produces an output, which is the logical AND of all those inputs. It is optional to represent the Logical AND with the symbol ‘.’

Logic AND Gates are available using digital circuits to produce the desired logical function and is given a symbol whose shape represents the logical operation of the AND gate. Because the Boolean expression for the logic AND function is defined as (.), which is a binary operation, AND gates can be cascaded together to form any number of individual inputs. However, commercial available AND gate IC’s are only available in standard 2, 3, or 4-input packages. If additional inputs are required, then standard AND gates will need to be cascaded together to obtain the required output value.

Boolean Expression Y = A.B.C.D

"If A and B and C and C are true, then Y is true"

This AND gate produces an output Y, which is the logical AND of inputs A, B, C, D.

Block Diagram


  1. Make the connections according to the IC pin diagram.
  2. The connections should be tight on trainer kit.
  3. The Vcc and ground should be applied carefully at the specified pin only.


We have learned the Dual 4-Input AND Gates IC according to the IC pin diagram.