U.S. Patent No. 3,585,517 - 06/15/1971 - Roger B. Herbert
Comments Concerning the Patent Gerald Stanley 03/03/2003: "Interleave of 2 Class-D or filterless Class-D. One of history's most reinvented class-D forms, this interleaved full-bridge was first invented by Roger Herbert of Westinghouse in 1968. The USPTO continues to issue more patents to this same invention annually."