# Logic gate

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A logic gate is an electronic component that can be used to conduct electricity based on a rule. The output of the gate is the result of applying this rule to one or more "sources". These sources may be two wires or the output of other logic gates. Logic gates are digital components. They normally work at only two levels of voltage, a positive level and a zero level. Commonly they work based on two states: On and Off. In the On state, voltage is present. In the Off state, the voltage is at zero. The On state usually uses a voltage in the range of 3.5 to 5 volts. This range can be lower for some uses. Logic gates compare the state at their inputs (source) to decide what the state at their output should be. A logic gate is on or active when its rules are correctly met. At this time, electricity is flowing through the gate and the voltage at its output is at the level of its On state. Logic gates are electronic versions of Boolean logic. Truth tables will tell you what the output will be, depending on the inputs.

## AND logic gate

A general idea of a symbol for an AND Logic Gate

With an AND gate, both inputs must be at an On state for the output to be On. Using the image at the right, if A and B are both in an On state, the output (out) will be an On state. If either A or B is in an Off state, the output will also be in an Off state. A and B must be On for the output to be On.

Truth table

A B Output
Off Off Off
On Off Off
Off On Off
On On On

## OR logic gate

A general idea of a symbol for an OR Logic Gate

With an OR gate, if either input is On, the output will be On. Using the image at the right, if either A or B is On, the output (out) will also be On. If both A and B are Off, the output will be Off.

Truth table

A B Output
Off Off Off
On Off On
Off On On
On On On

## NOT logic gate

The NOT logic gate has only one input so if our input is On then our output will be Off. The NOT logic gate simply changes the signal from On to Off or from Off to On. It is sometimes called an inverter.

A general idea of a symbol for a NOT Logic Gate

Truth table

A Output
Off On
On Off