Agree with Scrapheaper. It's most likely based on simple wave forms. Sounds like a sine or triangle bass with a saw on top. The key is the EQ job for sure. It seems to be a little muted on top and in the mids so you are left with a crisp, warm sound. May also have a bit of vibrato going on... perhaps a little chorusing as well, but to so much to lose the defined shape.