Fanout:-Maximum Gate we connect to output of any Logic gate.
so there is limited number of gate we connect the output of Logic Gate.hence there is some minimum condition required for operation of Logic Gate(Transistor).calculation of Fanout depend on current.
so what's the minimum current required to Drive the Transistor(TTL Logic)?How we calculate?
Similarly for operation Of transistor minimum Voltage required 0.7V.
Edit
Got the answer. There is No limitation of input or base current, to turn on the transistor. even if the Base current is tending to zero but still transistor will be on. but the problem is, that the transistor will not be in saturation but in the active region which causes the output voltage to enter the confusing region. (related to the Noise margin of the TTL). is this the correct explanation?