Tristate Buffer Output if Input is High-Z?
pkoning at equallogic.com
Thu Sep 29 16:51:13 CDT 2005
>>>>> "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
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
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