29 Sep
2005
29 Sep
'05
12:13 p.m.
It sounds like the tristate buffers don't do
exactly what I would
like, although I think I can make it work with more logic in front of
the control line for the buffer.
However, doing a bit more research, it looks like what I really need
is a Transmission Gate. The important difference is that a
transmission gate will pass the input regardless of its state, so L
passes L, H passes H and Z passes as Z. The disadvantage is that if
you have a noisy signal, the TG doesn't clean it up at all the way a
TB will.
The catch is that I cannot find one listed anywhere as a part that
one can actually buy. Are transmission gates purchasable parts? Or
are they just something they discussed in my VLSI textbook?
An analogue switch IC is a similar device, and those do exist. The
problem is finding one that will switch quickly enough (I would guess in
a few nanoseconds) for this application.
Also remmeber that analogue switches don't buffer the signal, you don't
get an increased drive current if you use one.
-tony