Fan-in
Fan-in is the number of inputs a logic gate can handle.[1] For instance the fan-in for the AND gate shown in the figure is 3.[2] 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 of the device.[3][4] 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.[5]
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.
See also
- Fan-out, a related concept, which is the number of inputs that a given logic output drives.
References
- ^ "fan-in and fan-out". Intel. Retrieved 2021-11-12.
Fan-in refers to the maximum number of input signals that feed the input equations of a logic cell.
- ISBN 978-1-351-83456-8.
- ISBN 978-3-540-45373-4.
- ISBN 978-81-203-4187-6.
- .
Fan-in tree is a collection of subsequent fan-in signals with respect to a given node.
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