High speed A/D and D/A is a big research driver to much of their business. The advances they make in gigasample D/A fabrication, can apply across a wide range of their product portfolio. The cutting edge chips may not represent a huge chunk of silicon volume, but they are a big driver of profitability. The volume is also likely a lot higher than you realize: these ADCs/DACs are ubiquitous in modern digital radars of the type preferred by the US military.

It also forms a big part of their business to sell associated components that complement the converters: clock sources, PLLs, some discrete RF, etc.