Fan In and Fan Out are characteristics of Digital ICs. Digital ICs are complete functioning logic networks. Typically, a Digital IC requires only a power supply, I/P (input) and O/P (output). Here are the definitions of Fan In and Fan Out.
Fan In: The fan-in defined as the maximum number of inputs that a logic gate can accept. If number of input exceeds, the output will be undefined or incorrect. It is specified by manufacturer and is provided in the data sheet.
Fan Out: The fan-out is defined as the maximum number of inputs (load) that can be connected to the output of a gate without degrading the normal operation. Fan Out is calculated from the amount of current available in the output of a gate and the amount of current needed in each input of the connecting gate. It is specified by manufacturer and is provided in the data sheet. Exceeding the specified maximum load may cause a malfunction because the circuit will not be able supply the demanded power.
The difference between these two characteristics of a digital IC is significant from the definitions above.
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