Logic gate facts for kids

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 "inputs". These inputs 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 zero level. Commonly they work based on two states: On and Off. In the On state, voltage is positive. 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 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

AND gates have two inputs. The output of an AND gate is on only if both inputs are on. If at least one of the inputs are off, the output will be off.

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.

OR logic gate

A general idea of a symbol for an OR Logic Gate

OR gates have two inputs. The output of an OR gate will be on if at least one of the inputs are on. If both inputs are off, the output will be off.

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.

NOT logic gate

The NOT logic gate has only one input. If the input is On then the output will be Off. In other words, the NOT logic gate 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

XOR logic gate

A general idea of a symbol for a XOR Logic Gate

XOR gates have two inputs. The output of a XOR gate will be true only if the two inputs are different from each other. If both inputs are the same, the output will be off.

Images for kids

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  A synchronous 4-bit up/down decade counter symbol (74LS192) in accordance with ANSI/IEEE Std. 91-1984 and IEC Publication 60617-12.

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  The 7400 chip, containing four NANDs. The two additional pins supply power (+5 V) and connect the ground.

See also

In Spanish: Puerta lógica para niños