Tristate Buffer Output if Input is High-Z?

Jeff> However, doing a bit more research, it looks like what I really Jeff> need is a Transmission Gate. The important difference is that Jeff> a transmission gate will pass the input regardless of its Jeff> state, so L passes L, H passes H and Z passes as Z. The Jeff> disadvantage is that if you have a noisy signal, the TG doesn't Jeff> clean it up at all the way a TB will. Jeff> The catch is that I cannot find one listed anywhere as a part Jeff> that one can actually buy. Are transmission gates purchasable Jeff> parts? Or are they just something they discussed in my VLSI Jeff> textbook? I have never heard that term, but what you describe is a common device. One term is "bilateral switch; you can find one in 4000 series logic. There is also the brand name "QuickSwitch", the same thing but substantially higher speed ratings. Basically, these are just FET switches. You can think of a FET as a voltage controlled resistor, and in these switches input and output are pretty much interchangeable (that's why it's called "bilateral"). You can make your own out of discrete FETs if you prefer, but the packaged ones should serve. You might check the data sheet to see if the 4000 series switch is fast enough; it may well be, and it should be readily available. paul