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Carsten Milkau/NOT Gate

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Revision as of 07:13, 22 July 2018 by 89.16.148.86 (talk) (Definition: names x and y for inputs/outputs in truth table)

NOT Gate

A NOT gate, sometimes also called inverter, is a circuit that outputs the value that was not input. It has a single input and output, and each can only take one of two pre-defined values (typically 0 and 1). Whatever the input value is selected, the output value will be the other of the two.

Definition

value table
inputs outputs
x y
0 1
1 0

Connectors

  • Input x: one of two values (0 or 1)
  • Output y: the other of the two values

Implementation

NOT gates can often be avoided by modifying the circuit. For instance, an OR Gate with two NOT gates connected to its inputs and outputs can always be replaced by an AND gate with just one NOT gate connected.

Unfortunately, there is no single-component implementation of a NOT gate. However, if you happen to have a data signal with a known value (like a memory containing a constant), often you can feed this signal into a single component in order to turn it into a NOT gate.

Using A Less-Than Comparator

CompareUnit.png

If you have a circuit available (e.g. a constant memory) that has a value b known to stay between 0 and 1 (but not 0), you can turn a Compare Unit into a logic NOT gate by comparing the input x to b, i.e.

y = (x < b)
circuit setup
unit unit type connector/setting source / value
compare 1 Compare Unit Input 1 x (input)
Input 2 b (constant or bounded value)
Operation Selector Lesser
Output y (output)

Using An Equality Comparator

CompareUnit.png

If you have a circuit output available that is known to be zero when the NOT gate is used (e.g. a constant memory), you can turn a Compare Unit into a logic NOT gate by comparing the input x to 0, i.e.

y = (x = 0)
circuit setup
unit unit type connector/setting source / value
compare 1 Compare Unit Input 1 x (input)
Input 2 0 (constant)
Operation Selector Equals
Output y (output)

Using Subtraction

MathUnit.png

If you do not use 0 and 1 as the two possible input values of the inverter, you can use subtraction for implementation. In this case, you need a constant that is exactly the mean of the two input values, i.e.

y = (m - x)

where m = (a + b)/2 is the mean of the two allowed input values, (called a and b here).

Circuit setup
unit unit type connector/setting source/value
math 1 Math Unit Input 1 x (input)
Input 2 m (constant, see above)
Operation Subtract
Output y (output)