Logic gates are physical components in a circuit that control the flow of a signal by implementing a Boolean function, processing a signal to binary information. Logic gates are foundational in logic circuits, or in any electronic circuit process that involves digital to analogue signal conversion, or the flow of digital information. Logic gates are primarily implemented using diodes or transistors as electrical switches, but can also be constructed using electromagnetic relays (relay logic), vacuum tubes, optics, molecules, fluidic logic, pneumatic logic, or even mechanical elements. You can learn more in our logic gates guide.
Types of Logic Gate
Logic gates have distinct logic functions. The most common of these are known as basic gates. These include:
- AND Gates - these gates have multiple inputs that are processed into a single signal output depending on the positive combination of high signals in the inputs. It will only produce a high signal if both inputs register as high (e.g. two ones will result in a one, otherwise, it will have an output of zero).
- OR Gates - similar to the AND gate, an OR gate has multiple inputs and a single output. In this case, it does not require a positive combination of one signals but will implement logical produce a high signal if one or all of the inputs are high. (e.g a one and a zero, or two ones, may produce a high signal, but two zeros will produce zeros.)
- NOT Gates -also known as inverters, the NOT gates will process the signal as the opposite of its value (eg. a one will invert as a zero, and a zero will invert as a 1.)
There are also combined function logic gates that modify typical functions with an inversion.
- NAND Gate - unlike an AND gate, NAND will process two high signals as a zero and all other combinations as a one.
- NOR Gate - unlike an OR gate, this will produce a one if the inputs register a zero signal in any combination, rather than a high signal.
- Buffer Gate - a buffer logic gate behaves in the opposite manner of a NOT gate, in that it passes a signal unchanged from input to output.
As CPUs employ binary logic, logic gates are essentially the building blocks of computers. As such, they can be found in many kinds of digital circuits such as:
- Encoders & Decoders
- Multiplexers & Demultiplexers
- Full and half adders