| Electronics > Beginners |
| Logic gates |
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| Keosintal:
Hi I am confused about logic gates. Are they physical component or what? I mean, do they sell these logic gates as individual components or is it some kind of programming inside an IC? |
| Mr. Scram:
A logic gate is an abstract component. They can be built from actual components in different ways using different technologies. If you look at the link at the bottom of my post, you'll find how an AND gate can be built using different types of basic components like transistors or diodes. By abstracting a logic gate you separate the underlying technology and its function. It makes designing an architecture and structure of a chip a little easier, as you don't have to deal with a lot of housekeeping. In earlier years logic gates mostly came packaged individually in ICs. Of course an IC also needs power and a few other things, as it's not an abstracted logic gate any more. These were mostly abstracted logic gates made into a physical thing. Combine different of these physical logic gate ICs in the right way and you can build a simple computer. You still find a lot of similar basic logic gate ICs in equipment today, usually performing glue logic functions. These are commonly chips of the HC74 family. Nowadays logic gates tend to be packaged together in much more integrated ways, like in microprocessors or other chips with a specific function. That way literally millions or billions of logic gates can be stuck together on a single chip. Most chips have an architecture, which is the layout of the logic gates inside the chip and thus also the layout of the actual components in the chip. https://en.wikipedia.org/wiki/AND_gate |
| Zero999:
Yes a gate is made of many other components. They can be switched and relays, transistors or thermionic tubes. Nowadays gates are mostly made of MOSFETs and fabricated on ICs. Glue logic containing individual gates is still available, but it's not as common as it used to be. Most IC packages contain four gates, but six and eight is common for NOT gates and line drivers and single gate packages exist in surface mount format, to save space. Some data sheets of logic gates in the 74HC(T) series. https://assets.nexperia.com/documents/data-sheet/74HC_HCT00.pdf https://assets.nexperia.com/documents/data-sheet/74HC_HCT1G00.pdf https://assets.nexperia.com/documents/data-sheet/74HC_HCT14.pdf https://assets.nexperia.com/documents/data-sheet/74HC_HCT1G14.pdf https://assets.nexperia.com/documents/data-sheet/74HC_HCT240.pdf https://assets.nexperia.com/documents/data-sheet/74HC_HCT02.pdf https://assets.nexperia.com/documents/data-sheet/74HC_HCT1G02.pdf |
| tautech:
Have a play with their functionality here: https://tams.informatik.uni-hamburg.de/applets/hades/webdemos/10-gates/00-gates/chapter.html |
| Zero999:
Here's a tutorial on how to make various logic gates from MOSFETs, inside the CD4007 transistor array. https://wiki.analog.com/university/courses/electronics/electronics-lab-28 |
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