But how do you plan to correlate the data? With a multiplexer you'll get a piece of data from time X on channel 1, a piece of data from time X+1 on channel 2. Much like a video monitor multiplexer you sometimes see to watch multiple cameras on one monitor. You can see what happens everywhere but you can't see what happens at the same time.
Samples will be in their original time moment. I will not correlate the data in the time and move samples.
Lets assume that I have 1GS/s scope and 3-channel multiplexer. I will see on recorded data:
1. ch. sample | mux switch to 2. ch. | 2. ch. sample | mux switch to 3. ch | 3. ch sample | mux switch to 1. ch. | ...
0 - 1ns : 1. channel sample
1ns - 10ns : mux switch to 2. ch.
10ns - 11ns: 2. channel sample
11ns - 21ns: mux switch to 3. ch.
21ns - 22ns: 3. channel sample
22ns - 32ns: mux switch to 1. ch.
32ns - 33ns: 1. channel sample
33ns - 43ns : mux switch to 2. ch.
43ns - 44ns: 2. channel sample
44ns - 54ns: mux switch to 3. ch.
54ns - 55ns: 3. channel sample
55ns - 65ns: mux switch to 1. ch.
65ns - 66ns: 1. channel sample
66ns - 76ns : mux switch to 2. ch.
76ns - 77ns: 2. channel sample
77ns - 87ns: mux switch to 3. ch.
87ns - 88ns: 3. channel sample
88ns - 98ns: mux switch to 1. ch.
It is always 33ns sample rate.
I assumed 10 ns time for mux switching operation and stabilization, but I think it may be longer. I hope not. I could have higher sample rate if I would have faster multiplexer.
Now I have 30 MSamples 3-channel oscilloscope with accuracy in time 33ns.
I don't need to know did the scope recorded the sample. If 1GS/s is set I will switch the multiplexer after 1ns and that is all. If I would be not synchronized with adc clock I would increase this time to 2ns, but I will loose sample rate or just synchronize with adc.
So, I also need fast 1xN multiplexer with lot of channels