Why NAND & NOR Gates are Necessary for LATCH Circuits

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Discussion Overview

The discussion centers on the necessity of NAND and NOR gates in the construction of latch circuits, exploring whether other types of logic gates can be used instead. Participants examine the fundamental roles of these gates in digital circuit design, particularly in relation to combinatorial logic and the requirements of latch functionality.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants assert that NAND and NOR gates are essential for latch circuits due to their ability to create the necessary inverter functionality.
  • Others argue that it is possible to construct latch circuits using other logic gates, as all combinatorial logic can theoretically be built from AND, OR, and NOT gates.
  • A participant mentions that while NAND and NOR gates are commonly used, they can be constructed from combinations of inverters, AND gates, and OR gates.
  • One participant highlights that a transistor with gain functions as an inverter, suggesting that the design of AND gates inherently relies on NAND gates followed by an inversion.

Areas of Agreement / Disagreement

Participants express differing views on whether latch circuits can be constructed using gates other than NAND and NOR. There is no consensus, as some maintain that these gates are necessary while others propose alternatives.

Contextual Notes

Participants reference the fundamental boolean operations and the technical reasons for preferring NAND and NOR gates in integrated circuits, but the discussion does not resolve the implications of these choices or the completeness of the arguments presented.

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TL;DR
why NAND AND NOR gates alone are used to form a LATCH circuit
Why we cannot make a LATCH circuit with logic gates other than NAND and NOR gates.?
 
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Avanthica said:
TL;DR Summary: why NAND AND NOR gates alone are used to form a LATCH circuit

Why we cannot make a LATCH circuit with logic gates other than NAND and NOR gates.?
I think you can. However, recognize that all combinatorial logic can be (in fact often are) constructed from NAND and NOR gates. The fundamental boolean operations are AND, OR, and INVERT (or NOT), everything can be constructed from these. For technical reasons, it is usually easier to just make NAND and NOR gates as the basis for all higher complexity digital circuits in ICs.
 
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Avanthica said:
Why we cannot make a LATCH circuit with logic gates other than NAND and NOR gates.?
Because you need an inverter somewhere in a latch. Try to design a latch without a NOT gate and see what happens.

A transistor with gain is inherently an inverter. To make an AND gate, you must build a NAND gate, then invert the output with a NOT. AND is therefore slower than NAND.
 
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