I need a MUX 8-1 with a very fast propagation delay; <10ns. I was searching Digikey and found a category of digital muxes called FET multiplexers, and their propagation delay is insanely fast < 0.25ns, which seems too good to be true.
What are the advantages and disadvantages between using a FET multiplexer such as the SN74CBT3251 and a regular digital one such as the CD74AC251 other than propagation delay time differences?
A FET multiplexer seems like an analog one, but it's listed under digital on Digikey…
Best Answer
You are looking for an 8 to 1 MUX with a very fast propagation delay <10ns.
THe Analog Mux is a passive switch, is bi-directional (1:8 or 8:1) but meets your speed requirements if you can provide low impedance source and some terminator resistance (passive or active).
The Digital MUX is unidirectional 8 to 1 with complementary buffered outputs are slower. Both have OE for a similar tri-state output.
If you are considering digital MUX's and need optimal speed, it would seem the ANALOG Mux will satisfy your requirements. THere will be glitches on the output signal during address transitions from high output impedance and capacitance, but that's normal. There will be some source loading effects when output load is connected to each input, but Ok for say low 50 ohm source and say 500 ohm terminator.
If using this for an analog MUX/DEMUX then time constants will different from specs according to difference in RC loads and transmission line effects.