Build your own Apollo Guidance Computer
ggs at shiresoft.com
Tue Dec 19 17:41:03 CST 2006
der Mouse wrote:
>> 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.)
LS usually has the speed of TTL with the power dissipation of L.
>> 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.
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
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