Study Notes on Logic Gates

Logic Gates

Logic Gates Explained

  • Logic gates are defined as the fundamental components of all digital circuits and systems.
  • A logic gate is essentially an electronic circuit constructed using various components including diodes, transistors, resistors, capacitors, etc.
  • They are the simplest types of digital components.
  • A logic gate performs a logical operation on one or more digital inputs and results in a single digital output.
  • Typical configuration involves most logic gates having two inputs and one output.
  • Inputs and outputs must adhere to binary values, either 1 or 0, as logic gates are digital components.

Functionality of Logic Gates

  • Logic gates are instrumental in controlling states (on/off) based on particular combinations of inputs.
  • A truth table serves as a tool to illustrate the output corresponding to all possible input combinations.
  • The truth table delineates the behavior of the logic gates comprehensively.

Types of Logic Gates

  • The principal types of logic gates include:
    • NOT Gate
    • AND Gate
    • OR Gate

NOT Gate

  • Characteristics:
    • The NOT gate operates with one input and one output.
    • Its function involves inverting the value of the input it receives.
NOT Gate Truth Table
InputOutput
01
10
Application of NOT Gate
  • An example of a NOT gate application is in a scenario where two light bulbs are utilized but only want one to be illuminated at a time:
    • A NOT gate is placed between the two light bulbs, ensuring that the digital signal responsible for turning one bulb on is always the inverse of the signal for the other bulb.
    • Consequently, when there exists a logic high (or 1) input, one light is illuminated while the other connected to the NOT gate remains off. Conversely, with a logic low (or 0) input, the second light activates due to the NOT gate's functionality.

AND Gate

  • Characteristics:
    • The AND gate is comprised of two inputs and one output.
    • The output will be 1 only if both input A and input B are 1; otherwise, the output is 0.
Application of AND Gate
  • An illustrative example:
    • Two switches, A and B, connected in series function as an AND logic gate, where the output lamp only illuminates when both switches A and B are closed.
    • Furthermore, in an alarm circuit, one input can represent a reed switch and the other an armed control. The alarm bell (output) will activate solely in the scenario where the alarm is active AND the reed switch circuit indicates that a door or window is opened.

OR Gate

  • Characteristics:
    • The OR gate operates with two inputs and one output.
    • The output becomes 1 if either input A, input B, or both, are 1; otherwise, the output results in 0.
Application of OR Gate
  • Example of an OR Gate in use:
    • In a circuit with parallel switches A and B, the OR gate is represented. If either switch A or B, or both switch on, the output lamp L will illuminate.
Additional Examples of OR Gate Applications
  • Practical applications include:
    • A landing light activates if either the switch on the landing or the switch located in the hall is in the ON position, or if both are ON.
    • A garage alarm triggers a siren if either the garage door is opened, the garage window is opened, or both are opened.