I actually did originally go back to the GitHub repo, but I missed this in the README:
"So far I have only built the B variant of the probe, that is, the probe with separate OP amps for the inputs."
So, that's why he doesn't discuss the others. He never built them.
> With your suggestion of what I should be looking for, how would you go about input termination without loading the UUT to the detriment of SI?
I would almost certainly want to grab the LMH6552 which is a fully-differential. It's input bias current isn't dramatically worse (110uA (about 10K Ohm) vs 34uA (about 30K Ohm)) than the LMH6702 that he used and likely wins by being matched/same temperature because same die/no PCB routing mismatch/etc.
"So far I have only built the B variant of the probe, that is, the probe with separate OP amps for the inputs."
So, that's why he doesn't discuss the others. He never built them.
> With your suggestion of what I should be looking for, how would you go about input termination without loading the UUT to the detriment of SI?
I would almost certainly want to grab the LMH6552 which is a fully-differential. It's input bias current isn't dramatically worse (110uA (about 10K Ohm) vs 34uA (about 30K Ohm)) than the LMH6702 that he used and likely wins by being matched/same temperature because same die/no PCB routing mismatch/etc.