19 Dec
2006
19 Dec
'06
3:41 p.m.
der Mouse wrote:
LS usually has the speed of TTL with the power dissipation of L.
Other variations:
74Hxx
74Lxx
74Sxx
74ASxx
74ALSxx
74Cxx
ECL is fast because it doesn't put the transistors into saturation or
cutoff (ie it's operating in the "linear region"). This means that no
time is required to move "large" amounts of charge (electrons) into or
out of the base of the transistor which is necessary to "saturate" the
transistor. This is why it is so power hungry...it's operating in the
"linear" region so current is always flowing through it and it's acting
as a resistor (ie causing a voltage drop across the part).
--
TTFN - Guy
Is there a
guide somewhere to the different families of logic, such
as RTL, TTL, LSTTL (never heard of that one)
LSTTL = Low-power Schottky TTL: basically, TTL done with low-power
Schottky technology. (http://en.wikipedia.org/wiki/Schottky_barrier
has more than you probably want to know about what Schottky means as
applied to semiconductor logic.)
Also, some are Schmidt Triggered?
(Schmitt, I think.) I suspect most logic families have something
functionally equivalent to Schmitt triggers (inputs with hysteresis).
As for a guide to the families, I can't help much there. I know that
there exists CMOS which is signal-level-compatible with TTL (I think
they're the 74HCT parts), but that's about where my knowledge ends.
You might also add ECL to your list. It stands for Emitter-Coupled
Logic, and I have gained the impression that it's fast and
power-hungry, but further deponent sayeth not.