Maximum operating frequency


Joined Jan 19, 2009
You can make a ballpark estimate based on the
way the logic is implemented (RTL, DTL, TTL,
ECL, CMOS). Basically, the limiting factor is the
parasitic capacitance of a transistor --- closing a
digital switch is limited by the time it takes to
charge the capacitance. To make faster logic,
one either figures out a way of making charging
faster (e.g. use a diode rather than a resistor) or
by not charging up the capacitor all the way
(e.g. not driving transistors to saturation in
common emitter logic).

As for the numbers, I remember off the top of
my head that CMOS goes up to a few
MegaHertz, but don't recall what the numbers
are for the other logic families.