The maximum number of standard digital inputs that the output of a logic gate can feed while maintaining valid voltage levels. Driving too many inputs draws excessive current, which degrades the logic high or low voltage and slows down the transition times due to accumulated input capacitance. If a signal must drive a massive number of destinations, designers insert buffer trees to multiply the driving capability.
Heard on the job
The clock signal has a massive fanout across the board, so we need to route it through a clock distribution buffer.
Also heard as
- fan-out
Do not mix it up with
- Fanin: Fanout measures driving capability for outgoing signals, while fanin measures the capacity for incoming signals.