logic gate Definition and Topics - 15 Discussions

A logic gate is an idealized model of computation or physical electronic device implementing a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and unlimited fan-out, or it may refer to a non-ideal physical device (see Ideal and real op-amps for comparison).
Logic gates are primarily implemented using diodes or transistors acting as electronic switches, but can also be constructed using vacuum tubes, electromagnetic relays (relay logic), fluidic logic, pneumatic logic, optics, molecules, or even mechanical elements. With amplification, logic gates can be cascaded in the same way that Boolean functions can be composed, allowing the construction of a physical model of all of Boolean logic, and therefore, all of the algorithms and mathematics that can be described with Boolean logic.
Logic circuits include such devices as multiplexers, registers, arithmetic logic units (ALUs), and computer memory, all the way up through complete microprocessors, which may contain more than 100 million gates. In modern practice, most gates are made from MOSFETs (metal–oxide–semiconductor field-effect transistors).
Compound logic gates AND-OR-Invert (AOI) and OR-AND-Invert (OAI) are often employed in circuit design because their construction using MOSFETs is simpler and more efficient than the sum of the individual gates.In reversible logic, Toffoli gates are used.

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  1. N

    Using delicate 5V IC to toggle 12V device with MOSFET, Diode, resistor

    Hey all, I have a 5v IC that is triggered by a sensor to unlock the 12v lock, I am using a NPN transistor as a switch with the 5v VCC as the gate, I need it to sink back to the GND of the IC without blowing it, is this safe? If not what changes would you suggest, it has been years since I've had...
  2. Delta2

    Ohmic Resistance and Logic gates

    Is ohmic resistance a "necessary evil" in order for transistors to be able to function as logic gates? I mean, I have seen some circuits for the NAND gate in RTL and TTL and they both seem to involve ohmic resistances. Can we make a super conducting NAND gate that will have total ohmic...
  3. peroAlex

    Designing a 2-bit Comparator with NOR gates

    At our class on digital structures, this assignment has been given. It's a preparation for upcoming lab work, and I'm not sure my design is correct. Is anyone please willing to check it out? 1. The problem statement, all variables, and given/known data Design a two-bit comparator using NOR gates...
  4. OrlandoLewis

    How to toggle and latch using logic gates?

    We're implementing Dots and Boxes to logic circuits and the we would like to automate the process of changing turns. If you know the game, the game changes turn when one move doesn't score a point or form two or more boxes. I was able to create overlapping XOR gates that alternates from high to...
  5. moenste

    Truth table of NAND gate

    Homework Statement (a) The diagram represents a NAND gate with two inputs, T1 and T2, and an output X. Copy the truth table above and complete it. Show how a NAND gate can become a NOT gate. (b) Draw up a truth table for the combination of NAND gates shown above. 2. The attempt at a...
  6. moenste

    Construct a truth table for the combination of logic gates

    Homework Statement Construct a truth table for the combination of logic gates shown above. 2. The attempt at a solution First of all the combination of logic gates with added letters to the combination: The truth table: I think it should be correct. But just want to be sure.
  7. moenste

    Simple logic gate

    Homework Statement Complete the truth table for the simple combination of logic gates shown above. 2. The attempt at a solution I think this should be correct, but just want to check, since I don't have a book answer to compare:
  8. C

    Transistor Logic Gate : NOT Gate Explanation?

    Hi everyone. I would like to ask about this light sensor using not gate circuit. I use LDR as an input and a LED as an output. I have tried this circuit in Proteus, and it works. When the LDR 'off', LED turns on, and vice versa. But i don't really understand about the working principle of this...
  9. R

    Logic Gates and Switches

    Hello, I'm currently studying a course in digital logic. The course is included in my IT program. And I have not taken a course in electronics yet; I will later. My question basically is: what is the output of a logic gate given that one input is neither connected to a high voltage nor...
  10. Y

    XAND gate?

    I've been reading Code: The Hidden Language of Computer Hardware and Software by Charles Petzold, and he described the 5 basic gates (AND, OR, NAND, NOR, & XOR) with extreme clarity. In the chapter about adding machines, he described that we needed a gate that relays only when it receives a 0...
  11. M

    How to use Logic gate in Breadboard circuit?

    I am a High school student, I have read about Logic gates but when it comes to practical use I am confused. I am building a small project where I want to use OR and AND gate, but I don't know In which form they are available in the market, how to connect them on breadboard and how to power them...
  12. ichabodgrant

    Comparator design using a 4-bit adder

    Homework Statement Hi, it's me again. Now I am going to design a 4-bit magnitude comparator using just ONE 4-bit adder and infinitely large number of gates (AND, OR, NOT, NAND, NOR, XOR, XNOR) for signed numbers (negative binary). Homework Equations A > B => A3barB3 + A2barB2x3 +...
  13. ichabodgrant

    Op-amp as a comparator (analog-to-digital conversion)

    Homework Statement Okay, This time it's an exam question. I am doing some past papers and there are questions about comparators which are not introduced in this course (this course is preliminary course for engineering students who are interested in electrical, electronic or computer...
  14. RaulTheUCSCSlug

    Using Arduino as a Logic Switch

    I want to supply some LED's and a motor from an outside source of electricity (i.e. a battery pack, wall outlet, batteries in series, etc.) and want to use the Arduino to be able to "switch" on and off these sources so that I am able to control long strands of LED's with the Arduino (for like a...
  15. C

    What is trivial and non-trivial gate in computing?

    My question seems like it should be posted in Computer Engineering section, but below is how I found this word. I was reading the textbook: Quantum Computation And Quantum Information - by Michael A. Nielsen and Issac L. Chuang. and I came across with the this word; "1.3.1 Single qubit gates...
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