29 Sep
2005
29 Sep
'05
2:51 p.m.
>>>> "Tony" == Tony Duell <ard
at p850ug1.demon.co.uk> writes:
> 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?
Tony> An analogue switch IC is a similar device, and those do
Tony> exist. The problem is finding one that will switch quickly
Tony> enough (I would guess in a few nanoseconds) for this
Tony> application.
No problem.
Quickswitches are rated to several hundred Megahertz. If that isn't
good enough, you can use microwave switch transistors. I don't know
the max switch rate of either, but presumably any transistor capable
of carrying microwave frequencies can switch on/off in a nanosecond or
better.
paul