I am not an expert in these laws, but at least for closed-source products I think that fast ADCs when implemented on a chip might be covered by section 3a001.a.5.a of
https://www.bis.doc.gov/index.php/documents/regulations-docs/2334-ccl3-8/file For designers residing outside the USA, or inside the USA but without holding US citizenship, this might prevent the finished integrated circuits from being sent to the designer. Sections 3D... and 3E... seem to try to cover software and technology (perhaps layouts?) that are for devices in 3A..., but I don't know whether being open-source would confer any kind of immunity from these requirements, and it might depend on the country that the designer lives in, whether it is allowable to make the design freely available and/or send it to the fab. These classifications are somewhat ridiculous (e.g. for many years any functional GSM phone would contain a synthesizer that used to be covered, and even today, any decent stereo audio amplifier with a CD player would potentially be 3a225), but ridiculous as these rules are, governments seem to (selectively) take them seriously (when that inconveniences somebody they don't like). Fortunately my ADC experience is so limited that I would not be able to make anything covered by these regulations, and I will for now choose to avoid the other categories as there is enough fun stuff that is not covered. Still, it would be great to get an authoritative legal opinion about what we should steer clear of, and what is ok.