Fan-in is the number of inputs a

logic gate A logic gate is an idealized or physical device implementing a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic ga ...

can handle. For instance the fan-in for the AND gate shown in the figure is 3. Physical logic gates with a large fan-in tend to be slower than those with a small fan-in. This is because the complexity of the input circuitry increases the input

capacitance Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized a ...

of the device. Using logic gates with higher fan-in will help in reducing the depth of a logic circuit; this is because circuit design is realized by the target logic family at a digital level, meaning any large fan-in logic gates are simply the smaller fan-in gates chained together in series at a given depth to widen the circuit instead. Fan-in tree of a node refers to a collection of signals that contribute to the input signal of that node. In quantum logic gates the fan-in always has to be equal to the number of outputs, the Fan-out. Gates for which the numbers of inputs and outputs differ would not be reversible ( unitary) and are therefore not allowed.

References

Logic gates {{Electronics-stub de:Fan-Out#Fan-In

See also

References