Logic Circuits

Understanding Logic Circuits

  • A Logic Circuit is a type of digital circuit which serves as the basic building block of digital systems like computers.
  • These circuits operate on logical inputs to produce logical outputs following certain logical relationships.

Types of Logic Gates

  • AND Gate: It gives a high output (1) only if all its inputs are high.
  • OR Gate: It gives a high output (1) if at least one of its inputs is high.
  • NOT Gate (Inverter): It gives a high output (1) when its input is low (0) and vice versa.
  • NAND Gate: It acts as an AND Gate followed by a NOT Gate, and gives a low output (0) only when all inputs are high.
  • NOR Gate: It behaves as an OR Gate followed by a NOT Gate, and produces a high output (0) if at least one of its inputs is high.
  • XOR Gate (Exclusive OR): It gives a high output (1) if an odd number of inputs are high.
  • XNOR Gate (Exclusive NOR): It gives a high output (1) if an even number of inputs are high.

Applied Use of Logic Gates

  • Half Adder: A logic circuit with two inputs and two outputs (Sum and Carry) that can be used in mathematics for binary addition.
  • Full Adder: A circuit further expanding on the Half Adder, which takes the carry from the previous addition into account. It is used to add three binary numbers.

Key Concepts in Logic Circuits

  • Truth Table: A systematic representation of a logic gates’ operation, it lists all possible input combinations and their corresponding outputs.
  • Boolean Algebra: Mathematical approach for describing and designing logical operations; very useful in simplifying complex logic circuits.
  • Logic Levels: Systems usually have two logic levels, high level (representing 1) and low level (representing 0).

Combinational vs Sequential Logic Circuits

  • Combinational Logic Circuit: Output is only dependent on the present input states. Examples include Adder, Subtractor, Decoder, Encoder.
  • Sequential Logic Circuit: Output depends not only on the present inputs but also the past history of inputs. Examples are Flip Flop, Counter, Memory Unit.