📖 IT Bible

Logic Gates

Logic Gates - allow our transistors to do more complex tasks, like decide where to send electrical signals depending on logical conditions. They tell a compute hot to perform binary calculations

  • specify rules for how to produce an electrical output based on one or more electrical inputs
  • used to represent 2 binary states: On or Off; takes in one or more of these binary states and determines whether to pass along an on or off signal
  • can be linked together to create complex electrical systems (circuits) that perform complicated binary calculations

Here’s a schematic drawing for a small circuit built with gates described above:

Recreated - Combined Circuit Schematic

Here is the truth table for this circuit:

A B A OR B A AND B NOT (A AND B) Output
0 0 0 0 1 0
0 1 1 0 1 1
1 0 1 0 1 1
1 1 1 1 0 0

6 Common Logic Gates:

  1. NOT Gate

    • simplest; only has one input signal
    • takes input signal and outputs a signal with opposite binary state
    • ex. input signal is “on”, then NOT Gate outputs “off” signal Pasted image 20260125184820

  2. AND Gate

    • involves 2 input signals, meaning 4 possible combinations on input values
    • AND rule outputs and “on” signal when BOTH inputs are “on”, otherwise output will be “off” Pasted image 20260125185027

  3. OR Gate

    • involves 2 input signals as well
    • OR rule outputs and “off” signal when BOTH inputs are “off”, otherwise output will be “on” Pasted image 20260125185206

  4. XOR Gate (aka exclusive OR Gate)

    • involves 2 input signals
    • XOR rule outputs an “on” signal when only one (but not both) of inputs are “on”, otherwise output signal will be “off” Pasted image 20260125185353

  5. NAND Gate (aka not-AND Gate)

    • involves 2 input signals
    • outputs an “off” signal only when both inputs are “on”, otherwise output will be “on”
    • outputs are opposite of AND outputs
    • combination of AND & NOT rules Pasted image 20260125185534

  6. XNOR Gate (aka not-XOR Gate)

    • involves 2 input signals
    • outputs “on” only when both inputs are the same (both “on” or both “off”), otherwise output will be “off”
    • takes the XOR output and runs it through the NOT rule
    • combination of XOR rule and NOT rule Pasted image 20260125185832

Key takeaways

Logic gates are the physical components that allow computers to make binary calculations.

  • Logic gates represent different rules for taking one or more binary inputs and outputting a specific binary value (“on” or “off”).
  • Logic gates can be linked so that the output of one gate serves as the input for other gates.
  • Circuits are complex electrical systems built by linking logic gates together. Computers are this kind of complex electrical system.